This code generates a CMPXCHG loop in order to implement atomic_fetch
bitwise operations. Because CMPXCHG is hard-coded to use rax (which
holds the BPF r0 value), it saves the _real_ r0 value into the
internal "ax" temporary register and restores it once the loop is
complete.
In the middle of the loop, the actual bitwise operation is performed
using src_reg. The bug occurs when src_reg is r0: as described above,
r0 has been clobbered and the real r0 value is in the ax register.
Therefore, perform this operation on the ax register instead, when
src_reg is r0.
Fixes: 981f94c3e9 ("bpf: Add bitwise atomic instructions")
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: KP Singh <kpsingh@kernel.org>
Link: https://lore.kernel.org/bpf/20210216125307.1406237-1-jackmanb@google.com
Since both sleepable and non-sleepable programs execute under migrate_disable
add recursion prevention mechanism to both types of programs when they're
executed via bpf trampoline.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210210033634.62081-5-alexei.starovoitov@gmail.com
Since sleepable programs don't migrate from the cpu the excution stats can be
computed for them as well. Reuse the same infrastructure for both sleepable and
non-sleepable programs.
run_cnt -> the number of times the program was executed.
run_time_ns -> the program execution time in nanoseconds including the
off-cpu time when the program was sleeping.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: KP Singh <kpsingh@kernel.org>
Link: https://lore.kernel.org/bpf/20210210033634.62081-4-alexei.starovoitov@gmail.com
PTR_TO_BTF_ID registers contain either kernel pointer or NULL.
Emit the NULL check explicitly by JIT instead of going into
do_user_addr_fault() on NULL deference.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20210202053837.95909-1-alexei.starovoitov@gmail.com
The x64 bpf jit expects bpf images converge within the given passes, but
it could fail to do so with some corner cases. For example:
l0: ja 40
l1: ja 40
[... repeated ja 40 ]
l39: ja 40
l40: ret #0
This bpf program contains 40 "ja 40" instructions which are effectively
NOPs and designed to be replaced with valid code dynamically. Ideally,
bpf jit should optimize those "ja 40" instructions out when translating
the bpf instructions into x64 machine code. However, do_jit() can only
remove one "ja 40" for offset==0 on each pass, so it requires at least
40 runs to eliminate those JMPs and exceeds the current limit of
passes(20). In the end, the program got rejected when BPF_JIT_ALWAYS_ON
is set even though it's legit as a classic socket filter.
To make bpf images more likely converge within 20 passes, this commit
pads some instructions with NOPs in the last 5 passes:
1. conditional jumps
A possible size variance comes from the adoption of imm8 JMP. If the
offset is imm8, we calculate the size difference of this BPF instruction
between the previous and the current pass and fill the gap with NOPs.
To avoid the recalculation of jump offset, those NOPs are inserted before
the JMP code, so we have to subtract the 2 bytes of imm8 JMP when
calculating the NOP number.
2. BPF_JA
There are two conditions for BPF_JA.
a.) nop jumps
If this instruction is not optimized out in the previous pass,
instead of removing it, we insert the equivalent size of NOPs.
b.) label jumps
Similar to condition jumps, we prepend NOPs right before the JMP
code.
To make the code concise, emit_nops() is modified to use the signed len and
return the number of inserted NOPs.
For bpf-to-bpf, we always enable padding for the extra pass since there
is only one extra run and the jump padding doesn't affected the images
that converge without padding.
After applying this patch, the corner case was loaded with the following
jit code:
flen=45 proglen=77 pass=17 image=ffffffffc03367d4 from=jump pid=10097
JIT code: 00000000: 0f 1f 44 00 00 55 48 89 e5 53 41 55 31 c0 45 31
JIT code: 00000010: ed 48 89 fb eb 30 eb 2e eb 2c eb 2a eb 28 eb 26
JIT code: 00000020: eb 24 eb 22 eb 20 eb 1e eb 1c eb 1a eb 18 eb 16
JIT code: 00000030: eb 14 eb 12 eb 10 eb 0e eb 0c eb 0a eb 08 eb 06
JIT code: 00000040: eb 04 eb 02 66 90 31 c0 41 5d 5b c9 c3
0: 0f 1f 44 00 00 nop DWORD PTR [rax+rax*1+0x0]
5: 55 push rbp
6: 48 89 e5 mov rbp,rsp
9: 53 push rbx
a: 41 55 push r13
c: 31 c0 xor eax,eax
e: 45 31 ed xor r13d,r13d
11: 48 89 fb mov rbx,rdi
14: eb 30 jmp 0x46
16: eb 2e jmp 0x46
...
3e: eb 06 jmp 0x46
40: eb 04 jmp 0x46
42: eb 02 jmp 0x46
44: 66 90 xchg ax,ax
46: 31 c0 xor eax,eax
48: 41 5d pop r13
4a: 5b pop rbx
4b: c9 leave
4c: c3 ret
At the 16th pass, 15 jumps were already optimized out, and one jump was
replaced with NOPs at 44 and the image converged at the 17th pass.
v4:
- Add the detailed comments about the possible padding bytes
v3:
- Copy the instructions of prologue separately or the size calculation
of the first BPF instruction would include the prologue.
- Replace WARN_ONCE() with pr_err() and EFAULT
- Use MAX_PASSES in the for loop condition check
- Remove the "padded" flag from x64_jit_data. For the extra pass of
subprogs, padding is always enabled since it won't hurt the images
that converge without padding.
v2:
- Simplify the sample code in the description and provide the jit code
- Check the expected padding bytes with WARN_ONCE
- Move the 'padded' flag to 'struct x64_jit_data'
Signed-off-by: Gary Lin <glin@suse.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210119102501.511-2-glin@suse.com
This adds instructions for
atomic[64]_[fetch_]and
atomic[64]_[fetch_]or
atomic[64]_[fetch_]xor
All these operations are isomorphic enough to implement with the same
verifier, interpreter, and x86 JIT code, hence being a single commit.
The main interesting thing here is that x86 doesn't directly support
the fetch_ version these operations, so we need to generate a CMPXCHG
loop in the JIT. This requires the use of two temporary registers,
IIUC it's safe to use BPF_REG_AX and x86's AUX_REG for this purpose.
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210114181751.768687-10-jackmanb@google.com
This adds two atomic opcodes, both of which include the BPF_FETCH
flag. XCHG without the BPF_FETCH flag would naturally encode
atomic_set. This is not supported because it would be of limited
value to userspace (it doesn't imply any barriers). CMPXCHG without
BPF_FETCH woulud be an atomic compare-and-write. We don't have such
an operation in the kernel so it isn't provided to BPF either.
There are two significant design decisions made for the CMPXCHG
instruction:
- To solve the issue that this operation fundamentally has 3
operands, but we only have two register fields. Therefore the
operand we compare against (the kernel's API calls it 'old') is
hard-coded to be R0. x86 has similar design (and A64 doesn't
have this problem).
A potential alternative might be to encode the other operand's
register number in the immediate field.
- The kernel's atomic_cmpxchg returns the old value, while the C11
userspace APIs return a boolean indicating the comparison
result. Which should BPF do? A64 returns the old value. x86 returns
the old value in the hard-coded register (and also sets a
flag). That means return-old-value is easier to JIT, so that's
what we use.
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210114181751.768687-8-jackmanb@google.com
The BPF_FETCH field can be set in bpf_insn.imm, for BPF_ATOMIC
instructions, in order to have the previous value of the
atomically-modified memory location loaded into the src register
after an atomic op is carried out.
Suggested-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210114181751.768687-7-jackmanb@google.com
A subsequent patch will add additional atomic operations. These new
operations will use the same opcode field as the existing XADD, with
the immediate discriminating different operations.
In preparation, rename the instruction mode BPF_ATOMIC and start
calling the zero immediate BPF_ADD.
This is possible (doesn't break existing valid BPF progs) because the
immediate field is currently reserved MBZ and BPF_ADD is zero.
All uses are removed from the tree but the BPF_XADD definition is
kept around to avoid breaking builds for people including kernel
headers.
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Björn Töpel <bjorn.topel@gmail.com>
Link: https://lore.kernel.org/bpf/20210114181751.768687-5-jackmanb@google.com
A later commit will need to lookup a subset of these opcodes. To
avoid duplicating code, pull out a table.
The shift opcodes won't be needed by that later commit, but they're
already duplicated, so fold them into the table anyway.
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210114181751.768687-4-jackmanb@google.com
The JIT case for encoding atomic ops is about to get more
complicated. In order to make the review & resulting code easier,
let's factor out some shared helpers.
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210114181751.768687-3-jackmanb@google.com
The case for JITing atomics is about to get more complicated. Let's
factor out some common code to make the review and result more
readable.
NB the atomics code doesn't yet use the new helper - a subsequent
patch will add its use as a side-effect of other changes.
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210114181751.768687-2-jackmanb@google.com
There is no particular reason for keeping the "sub 0, %rsp" insn within
the BPF's x64 JIT prologue.
When tail call code was skipping the whole prologue section these 7
bytes that represent the rsp subtraction could not be simply discarded
as the jump target address would be broken. An option to address that
would be to substitute it with nop7.
Right now tail call is skipping only first 11 bytes of target program's
prologue and "sub X, %rsp" is the first insn that is processed, so if
stack depth is zero then this insn could be omitted without the need for
nop7 swap.
Therefore, do not emit the "sub 0, %rsp" in prologue when program is not
making use of R10 register. Also, make the emission of "add X, %rsp"
conditional in tail call code logic and take into account the presence
of mentioned insn when calculating the jump offsets.
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200929204653.4325-3-maciej.fijalkowski@intel.com
Back when all of the callee-saved registers where always pushed to stack
in x64 JIT prologue, tail call counter was placed at the bottom of the
BPF program's stack frame that had a following layout:
+-------------+
| ret addr |
+-------------+
| rbp | <- rbp
+-------------+
| |
| free space |
| from: |
| sub $x,%rsp |
| |
+-------------+
| rbx |
+-------------+
| r13 |
+-------------+
| r14 |
+-------------+
| r15 |
+-------------+
| tail call | <- rsp
| counter |
+-------------+
In order to restore the callee saved registers, epilogue needed to
explicitly toss away the tail call counter via "pop %rbx" insn, so that
%rsp would be back at the place where %r15 was stored.
Currently, the tail call counter is placed on stack *before* the callee
saved registers (brackets on rbx through r15 mean that they are now
pushed to stack only if they are used):
+-------------+
| ret addr |
+-------------+
| rbp | <- rbp
+-------------+
| |
| free space |
| from: |
| sub $x,%rsp |
| |
+-------------+
| tail call |
| counter |
+-------------+
( rbx )
+-------------+
( r13 )
+-------------+
( r14 )
+-------------+
( r15 ) <- rsp
+-------------+
For the record, the epilogue insns consist of (assuming all of the
callee saved registers are used by program):
pop %r15
pop %r14
pop %r13
pop %rbx
pop %rcx
leaveq
retq
"pop %rbx" for getting rid of tail call counter was not an option
anymore as it would overwrite the restored value of %rbx register, so it
was changed to use the %rcx register.
Since epilogue can start popping the callee saved registers right away
without any additional work, the "pop %rcx" could be dropped altogether
as "leave" insn will simply move the %rbp to %rsp. IOW, tail call
counter does not need the explicit handling.
Having in mind the explanation above and the actual reason for that,
let's piggy back on "leave" insn for discarding the tail call counter
from stack and remove the "pop %rcx" from epilogue.
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200929204653.4325-2-maciej.fijalkowski@intel.com
This commit serves two things:
1) it optimizes BPF prologue/epilogue generation
2) it makes possible to have tailcalls within BPF subprogram
Both points are related to each other since without 1), 2) could not be
achieved.
In [1], Alexei says:
"The prologue will look like:
nop5
xor eax,eax // two new bytes if bpf_tail_call() is used in this
// function
push rbp
mov rbp, rsp
sub rsp, rounded_stack_depth
push rax // zero init tail_call counter
variable number of push rbx,r13,r14,r15
Then bpf_tail_call will pop variable number rbx,..
and final 'pop rax'
Then 'add rsp, size_of_current_stack_frame'
jmp to next function and skip over 'nop5; xor eax,eax; push rpb; mov
rbp, rsp'
This way new function will set its own stack size and will init tail
call
counter with whatever value the parent had.
If next function doesn't use bpf_tail_call it won't have 'xor eax,eax'.
Instead it would need to have 'nop2' in there."
Implement that suggestion.
Since the layout of stack is changed, tail call counter handling can not
rely anymore on popping it to rbx just like it have been handled for
constant prologue case and later overwrite of rbx with actual value of
rbx pushed to stack. Therefore, let's use one of the register (%rcx) that
is considered to be volatile/caller-saved and pop the value of tail call
counter in there in the epilogue.
Drop the BUILD_BUG_ON in emit_prologue and in
emit_bpf_tail_call_indirect where instruction layout is not constant
anymore.
Introduce new poke target, 'tailcall_bypass' to poke descriptor that is
dedicated for skipping the register pops and stack unwind that are
generated right before the actual jump to target program.
For case when the target program is not present, BPF program will skip
the pop instructions and nop5 dedicated for jmpq $target. An example of
such state when only R6 of callee saved registers is used by program:
ffffffffc0513aa1: e9 0e 00 00 00 jmpq 0xffffffffc0513ab4
ffffffffc0513aa6: 5b pop %rbx
ffffffffc0513aa7: 58 pop %rax
ffffffffc0513aa8: 48 81 c4 00 00 00 00 add $0x0,%rsp
ffffffffc0513aaf: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
ffffffffc0513ab4: 48 89 df mov %rbx,%rdi
When target program is inserted, the jump that was there to skip
pops/nop5 will become the nop5, so CPU will go over pops and do the
actual tailcall.
One might ask why there simply can not be pushes after the nop5?
In the following example snippet:
ffffffffc037030c: 48 89 fb mov %rdi,%rbx
(...)
ffffffffc0370332: 5b pop %rbx
ffffffffc0370333: 58 pop %rax
ffffffffc0370334: 48 81 c4 00 00 00 00 add $0x0,%rsp
ffffffffc037033b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
ffffffffc0370340: 48 81 ec 00 00 00 00 sub $0x0,%rsp
ffffffffc0370347: 50 push %rax
ffffffffc0370348: 53 push %rbx
ffffffffc0370349: 48 89 df mov %rbx,%rdi
ffffffffc037034c: e8 f7 21 00 00 callq 0xffffffffc0372548
There is the bpf2bpf call (at ffffffffc037034c) right after the tailcall
and jump target is not present. ctx is in %rbx register and BPF
subprogram that we will call into on ffffffffc037034c is relying on it,
e.g. it will pick ctx from there. Such code layout is therefore broken
as we would overwrite the content of %rbx with the value that was pushed
on the prologue. That is the reason for the 'bypass' approach.
Special care needs to be taken during the install/update/remove of
tailcall target. In case when target program is not present, the CPU
must not execute the pop instructions that precede the tailcall.
To address that, the following states can be defined:
A nop, unwind, nop
B nop, unwind, tail
C skip, unwind, nop
D skip, unwind, tail
A is forbidden (lead to incorrectness). The state transitions between
tailcall install/update/remove will work as follows:
First install tail call f: C->D->B(f)
* poke the tailcall, after that get rid of the skip
Update tail call f to f': B(f)->B(f')
* poke the tailcall (poke->tailcall_target) and do NOT touch the
poke->tailcall_bypass
Remove tail call: B(f')->C(f')
* poke->tailcall_bypass is poked back to jump, then we wait the RCU
grace period so that other programs will finish its execution and
after that we are safe to remove the poke->tailcall_target
Install new tail call (f''): C(f')->D(f'')->B(f'').
* same as first step
This way CPU can never be exposed to "unwind, tail" state.
Last but not least, when tailcalls get mixed with bpf2bpf calls, it
would be possible to encounter the endless loop due to clearing the
tailcall counter if for example we would use the tailcall3-like from BPF
selftests program that would be subprogram-based, meaning the tailcall
would be present within the BPF subprogram.
This test, broken down to particular steps, would do:
entry -> set tailcall counter to 0, bump it by 1, tailcall to func0
func0 -> call subprog_tail
(we are NOT skipping the first 11 bytes of prologue and this subprogram
has a tailcall, therefore we clear the counter...)
subprog -> do the same thing as entry
and then loop forever.
To address this, the idea is to go through the call chain of bpf2bpf progs
and look for a tailcall presence throughout whole chain. If we saw a single
tail call then each node in this call chain needs to be marked as a subprog
that can reach the tailcall. We would later feed the JIT with this info
and:
- set eax to 0 only when tailcall is reachable and this is the entry prog
- if tailcall is reachable but there's no tailcall in insns of currently
JITed prog then push rax anyway, so that it will be possible to
propagate further down the call chain
- finally if tailcall is reachable, then we need to precede the 'call'
insn with mov rax, [rbp - (stack_depth + 8)]
Tail call related cases from test_verifier kselftest are also working
fine. Sample BPF programs that utilize tail calls (sockex3, tracex5)
work properly as well.
[1]: https://lore.kernel.org/bpf/20200517043227.2gpq22ifoq37ogst@ast-mbp.dhcp.thefacebook.com/
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reflect the actual purpose of poke->ip and rename it to
poke->tailcall_target so that it will not the be confused with another
poke target that will be introduced in next commit.
While at it, do the same thing with poke->ip_stable - rename it to
poke->tailcall_target_stable.
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Currently, %rax is used to store the jump target when BPF program is
emitting the retpoline instructions that are handling the indirect
tailcall.
There is a plan to use %rax for different purpose, which is storing the
tail call counter. In order to preserve this value across the tailcalls,
adjust the BPF indirect tailcalls so that the target program will reside
in %rcx and teach the retpoline instructions about new location of jump
target.
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Introduce sleepable BPF programs that can request such property for themselves
via BPF_F_SLEEPABLE flag at program load time. In such case they will be able
to use helpers like bpf_copy_from_user() that might sleep. At present only
fentry/fexit/fmod_ret and lsm programs can request to be sleepable and only
when they are attached to kernel functions that are known to allow sleeping.
The non-sleepable programs are relying on implicit rcu_read_lock() and
migrate_disable() to protect life time of programs, maps that they use and
per-cpu kernel structures used to pass info between bpf programs and the
kernel. The sleepable programs cannot be enclosed into rcu_read_lock().
migrate_disable() maps to preempt_disable() in non-RT kernels, so the progs
should not be enclosed in migrate_disable() as well. Therefore
rcu_read_lock_trace is used to protect the life time of sleepable progs.
There are many networking and tracing program types. In many cases the
'struct bpf_prog *' pointer itself is rcu protected within some other kernel
data structure and the kernel code is using rcu_dereference() to load that
program pointer and call BPF_PROG_RUN() on it. All these cases are not touched.
Instead sleepable bpf programs are allowed with bpf trampoline only. The
program pointers are hard-coded into generated assembly of bpf trampoline and
synchronize_rcu_tasks_trace() is used to protect the life time of the program.
The same trampoline can hold both sleepable and non-sleepable progs.
When rcu_read_lock_trace is held it means that some sleepable bpf program is
running from bpf trampoline. Those programs can use bpf arrays and preallocated
hash/lru maps. These map types are waiting on programs to complete via
synchronize_rcu_tasks_trace();
Updates to trampoline now has to do synchronize_rcu_tasks_trace() and
synchronize_rcu_tasks() to wait for sleepable progs to finish and for
trampoline assembly to finish.
This is the first step of introducing sleepable progs. Eventually dynamically
allocated hash maps can be allowed and networking program types can become
sleepable too.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: KP Singh <kpsingh@google.com>
Link: https://lore.kernel.org/bpf/20200827220114.69225-3-alexei.starovoitov@gmail.com
The '==' expression itself is bool, no need to convert it to bool again.
This fixes the following coccicheck warning:
arch/x86/net/bpf_jit_comp32.c:1478:50-55: WARNING: conversion to bool not needed here
arch/x86/net/bpf_jit_comp32.c:1479:50-55: WARNING: conversion to bool not needed here
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200506140352.37154-1-yanaijie@huawei.com
When verifier_zext is true, we don't need to emit code
for zero-extension.
Fixes: 836256bf5f ("x32: bpf: eliminate zero extension code-gen")
Signed-off-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200423050637.GA4029@udknight
The current JIT clobbers the destination register for BPF_JSET BPF_X
and BPF_K by using "and" and "or" instructions. This is fine when the
destination register is a temporary loaded from a register stored on
the stack but not otherwise.
This patch fixes the problem (for both BPF_K and BPF_X) by always loading
the destination register into temporaries since BPF_JSET should not
modify the destination register.
This bug may not be currently triggerable as BPF_REG_AX is the only
register not stored on the stack and the verifier uses it in a limited
way.
Fixes: 03f5781be2 ("bpf, x86_32: add eBPF JIT compiler for ia32")
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Wang YanQing <udknight@gmail.com>
Link: https://lore.kernel.org/bpf/20200422173630.8351-2-luke.r.nels@gmail.com
The current JIT uses the following sequence to zero-extend into the
upper 32 bits of the destination register for BPF_LDX BPF_{B,H,W},
when the destination register is not on the stack:
EMIT3(0xC7, add_1reg(0xC0, dst_hi), 0);
The problem is that C7 /0 encodes a MOV instruction that requires a 4-byte
immediate; the current code emits only 1 byte of the immediate. This
means that the first 3 bytes of the next instruction will be treated as
the rest of the immediate, breaking the stream of instructions.
This patch fixes the problem by instead emitting "xor dst_hi,dst_hi"
to clear the upper 32 bits. This fixes the problem and is more efficient
than using MOV to load a zero immediate.
This bug may not be currently triggerable as BPF_REG_AX is the only
register not stored on the stack and the verifier uses it in a limited
way, and the verifier implements a zero-extension optimization. But the
JIT should avoid emitting incorrect encodings regardless.
Fixes: 03f5781be2 ("bpf, x86_32: add eBPF JIT compiler for ia32")
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Acked-by: Wang YanQing <udknight@gmail.com>
Link: https://lore.kernel.org/bpf/20200422173630.8351-1-luke.r.nels@gmail.com
This patch fixes an encoding bug in emit_stx for BPF_B when the source
register is BPF_REG_FP.
The current implementation for BPF_STX BPF_B in emit_stx saves one REX
byte when the operands can be encoded using Mod-R/M alone. The lower 8
bits of registers %rax, %rbx, %rcx, and %rdx can be accessed without using
a REX prefix via %al, %bl, %cl, and %dl, respectively. Other registers,
(e.g., %rsi, %rdi, %rbp, %rsp) require a REX prefix to use their 8-bit
equivalents (%sil, %dil, %bpl, %spl).
The current code checks if the source for BPF_STX BPF_B is BPF_REG_1
or BPF_REG_2 (which map to %rdi and %rsi), in which case it emits the
required REX prefix. However, it misses the case when the source is
BPF_REG_FP (mapped to %rbp).
The result is that BPF_STX BPF_B with BPF_REG_FP as the source operand
will read from register %ch instead of the correct %bpl. This patch fixes
the problem by fixing and refactoring the check on which registers need
the extra REX byte. Since no BPF registers map to %rsp, there is no need
to handle %spl.
Fixes: 622582786c ("net: filter: x86: internal BPF JIT")
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200418232655.23870-1-luke.r.nels@gmail.com
Overlapping header include additions in macsec.c
A bug fix in 'net' overlapping with the removal of 'version'
string in ena_netdev.c
Overlapping test additions in selftests Makefile
Overlapping PCI ID table adjustments in iwlwifi driver.
Signed-off-by: David S. Miller <davem@davemloft.net>
fmod_ret progs are emitted as:
start = __bpf_prog_enter();
call fmod_ret
*(u64 *)(rbp - 8) = rax
__bpf_prog_exit(, start);
test eax, eax
jne do_fexit
That 'test eax, eax' is working by accident. The compiler is free to use rax
inside __bpf_prog_exit() or inside functions that __bpf_prog_exit() is calling.
Which caused "test_progs -t modify_return" to sporadically fail depending on
compiler version and kconfig. Fix it by using 'cmp [rbp - 8], 0' instead of
'test eax, eax'.
Fixes: ae24082331 ("bpf: Introduce BPF_MODIFY_RETURN")
Reported-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: KP Singh <kpsingh@google.com>
Link: https://lore.kernel.org/bpf/20200311003906.3643037-1-ast@kernel.org
The current x32 BPF JIT is incorrect for JMP32 JSET BPF_X when the upper
32 bits of operand registers are non-zero in certain situations.
The problem is in the following code:
case BPF_JMP | BPF_JSET | BPF_X:
case BPF_JMP32 | BPF_JSET | BPF_X:
...
/* and dreg_lo,sreg_lo */
EMIT2(0x23, add_2reg(0xC0, sreg_lo, dreg_lo));
/* and dreg_hi,sreg_hi */
EMIT2(0x23, add_2reg(0xC0, sreg_hi, dreg_hi));
/* or dreg_lo,dreg_hi */
EMIT2(0x09, add_2reg(0xC0, dreg_lo, dreg_hi));
This code checks the upper bits of the operand registers regardless if
the BPF instruction is BPF_JMP32 or BPF_JMP64. Registers dreg_hi and
dreg_lo are not loaded from the stack for BPF_JMP32, however, they can
still be polluted with values from previous instructions.
The following BPF program demonstrates the bug. The jset64 instruction
loads the temporary registers and performs the jump, since ((u64)r7 &
(u64)r8) is non-zero. The jset32 should _not_ be taken, as the lower
32 bits are all zero, however, the current JIT will take the branch due
the pollution of temporary registers from the earlier jset64.
mov64 r0, 0
ld64 r7, 0x8000000000000000
ld64 r8, 0x8000000000000000
jset64 r7, r8, 1
exit
jset32 r7, r8, 1
mov64 r0, 2
exit
The expected return value of this program is 2; under the buggy x32 JIT
it returns 0. The fix is to skip using the upper 32 bits for jset32 and
compare the upper 32 bits for jset64 only.
All tests in test_bpf.ko and selftests/bpf/test_verifier continue to
pass with this change.
We found this bug using our automated verification tool, Serval.
Fixes: 69f827eb6e ("x32: bpf: implement jitting of JMP32")
Co-developed-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200305234416.31597-1-luke.r.nels@gmail.com
When multiple programs are attached, each program receives the return
value from the previous program on the stack and the last program
provides the return value to the attached function.
The fmod_ret bpf programs are run after the fentry programs and before
the fexit programs. The original function is only called if all the
fmod_ret programs return 0 to avoid any unintended side-effects. The
success value, i.e. 0 is not currently configurable but can be made so
where user-space can specify it at load time.
For example:
int func_to_be_attached(int a, int b)
{ <--- do_fentry
do_fmod_ret:
<update ret by calling fmod_ret>
if (ret != 0)
goto do_fexit;
original_function:
<side_effects_happen_here>
} <--- do_fexit
The fmod_ret program attached to this function can be defined as:
SEC("fmod_ret/func_to_be_attached")
int BPF_PROG(func_name, int a, int b, int ret)
{
// This will skip the original function logic.
return 1;
}
The first fmod_ret program is passed 0 in its return argument.
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200304191853.1529-4-kpsingh@chromium.org
* Split the invoke_bpf program to prepare for special handling of
fmod_ret programs introduced in a subsequent patch.
* Move the definition of emit_cond_near_jump and emit_nops as they are
needed for fmod_ret.
* Refactor branch target alignment into its own generic helper function
i.e. emit_align.
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200304191853.1529-3-kpsingh@chromium.org
As we need to introduce a third type of attachment for trampolines, the
flattened signature of arch_prepare_bpf_trampoline gets even more
complicated.
Refactor the prog and count argument to arch_prepare_bpf_trampoline to
use bpf_tramp_progs to simplify the addition and accounting for new
attachment types.
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200304191853.1529-2-kpsingh@chromium.org
The patch introduces BPF_MAP_TYPE_STRUCT_OPS. The map value
is a kernel struct with its func ptr implemented in bpf prog.
This new map is the interface to register/unregister/introspect
a bpf implemented kernel struct.
The kernel struct is actually embedded inside another new struct
(or called the "value" struct in the code). For example,
"struct tcp_congestion_ops" is embbeded in:
struct bpf_struct_ops_tcp_congestion_ops {
refcount_t refcnt;
enum bpf_struct_ops_state state;
struct tcp_congestion_ops data; /* <-- kernel subsystem struct here */
}
The map value is "struct bpf_struct_ops_tcp_congestion_ops".
The "bpftool map dump" will then be able to show the
state ("inuse"/"tobefree") and the number of subsystem's refcnt (e.g.
number of tcp_sock in the tcp_congestion_ops case). This "value" struct
is created automatically by a macro. Having a separate "value" struct
will also make extending "struct bpf_struct_ops_XYZ" easier (e.g. adding
"void (*init)(void)" to "struct bpf_struct_ops_XYZ" to do some
initialization works before registering the struct_ops to the kernel
subsystem). The libbpf will take care of finding and populating the
"struct bpf_struct_ops_XYZ" from "struct XYZ".
Register a struct_ops to a kernel subsystem:
1. Load all needed BPF_PROG_TYPE_STRUCT_OPS prog(s)
2. Create a BPF_MAP_TYPE_STRUCT_OPS with attr->btf_vmlinux_value_type_id
set to the btf id "struct bpf_struct_ops_tcp_congestion_ops" of the
running kernel.
Instead of reusing the attr->btf_value_type_id,
btf_vmlinux_value_type_id s added such that attr->btf_fd can still be
used as the "user" btf which could store other useful sysadmin/debug
info that may be introduced in the furture,
e.g. creation-date/compiler-details/map-creator...etc.
3. Create a "struct bpf_struct_ops_tcp_congestion_ops" object as described
in the running kernel btf. Populate the value of this object.
The function ptr should be populated with the prog fds.
4. Call BPF_MAP_UPDATE with the object created in (3) as
the map value. The key is always "0".
During BPF_MAP_UPDATE, the code that saves the kernel-func-ptr's
args as an array of u64 is generated. BPF_MAP_UPDATE also allows
the specific struct_ops to do some final checks in "st_ops->init_member()"
(e.g. ensure all mandatory func ptrs are implemented).
If everything looks good, it will register this kernel struct
to the kernel subsystem. The map will not allow further update
from this point.
Unregister a struct_ops from the kernel subsystem:
BPF_MAP_DELETE with key "0".
Introspect a struct_ops:
BPF_MAP_LOOKUP_ELEM with key "0". The map value returned will
have the prog _id_ populated as the func ptr.
The map value state (enum bpf_struct_ops_state) will transit from:
INIT (map created) =>
INUSE (map updated, i.e. reg) =>
TOBEFREE (map value deleted, i.e. unreg)
The kernel subsystem needs to call bpf_struct_ops_get() and
bpf_struct_ops_put() to manage the "refcnt" in the
"struct bpf_struct_ops_XYZ". This patch uses a separate refcnt
for the purose of tracking the subsystem usage. Another approach
is to reuse the map->refcnt and then "show" (i.e. during map_lookup)
the subsystem's usage by doing map->refcnt - map->usercnt to filter out
the map-fd/pinned-map usage. However, that will also tie down the
future semantics of map->refcnt and map->usercnt.
The very first subsystem's refcnt (during reg()) holds one
count to map->refcnt. When the very last subsystem's refcnt
is gone, it will also release the map->refcnt. All bpf_prog will be
freed when the map->refcnt reaches 0 (i.e. during map_free()).
Here is how the bpftool map command will look like:
[root@arch-fb-vm1 bpf]# bpftool map show
6: struct_ops name dctcp flags 0x0
key 4B value 256B max_entries 1 memlock 4096B
btf_id 6
[root@arch-fb-vm1 bpf]# bpftool map dump id 6
[{
"value": {
"refcnt": {
"refs": {
"counter": 1
}
},
"state": 1,
"data": {
"list": {
"next": 0,
"prev": 0
},
"key": 0,
"flags": 2,
"init": 24,
"release": 0,
"ssthresh": 25,
"cong_avoid": 30,
"set_state": 27,
"cwnd_event": 28,
"in_ack_event": 26,
"undo_cwnd": 29,
"pkts_acked": 0,
"min_tso_segs": 0,
"sndbuf_expand": 0,
"cong_control": 0,
"get_info": 0,
"name": [98,112,102,95,100,99,116,99,112,0,0,0,0,0,0,0
],
"owner": 0
}
}
}
]
Misc Notes:
* bpf_struct_ops_map_sys_lookup_elem() is added for syscall lookup.
It does an inplace update on "*value" instead returning a pointer
to syscall.c. Otherwise, it needs a separate copy of "zero" value
for the BPF_STRUCT_OPS_STATE_INIT to avoid races.
* The bpf_struct_ops_map_delete_elem() is also called without
preempt_disable() from map_delete_elem(). It is because
the "->unreg()" may requires sleepable context, e.g.
the "tcp_unregister_congestion_control()".
* "const" is added to some of the existing "struct btf_func_model *"
function arg to avoid a compiler warning caused by this patch.
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200109003505.3855919-1-kafai@fb.com
>From Intel 64 and IA-32 Architectures Optimization Reference Manual,
3.4.1.4 Code Alignment, Assembly/Compiler Coding Rule 11: All branch
targets should be 16-byte aligned.
This commits aligns branch targets according to the Intel manual.
The nops used to align branch targets make the dispatcher larger, and
therefore the number of supported dispatch points/programs are
descreased from 64 to 48.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191213175112.30208-7-bjorn.topel@gmail.com
The BPF dispatcher is a multi-way branch code generator, mainly
targeted for XDP programs. When an XDP program is executed via the
bpf_prog_run_xdp(), it is invoked via an indirect call. The indirect
call has a substantial performance impact, when retpolines are
enabled. The dispatcher transform indirect calls to direct calls, and
therefore avoids the retpoline. The dispatcher is generated using the
BPF JIT, and relies on text poking provided by bpf_arch_text_poke().
The dispatcher hijacks a trampoline function it via the __fentry__ nop
of the trampoline. One dispatcher instance currently supports up to 64
dispatch points. A user creates a dispatcher with its corresponding
trampoline with the DEFINE_BPF_DISPATCHER macro.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191213175112.30208-3-bjorn.topel@gmail.com
Given that we have BPF_MOD_NOP_TO_{CALL,JUMP}, BPF_MOD_{CALL,JUMP}_TO_NOP
and BPF_MOD_{CALL,JUMP}_TO_{CALL,JUMP} poke types and that we also pass in
old_addr as well as new_addr, it's a bit redundant and unnecessarily
complicates __bpf_arch_text_poke() itself since we can derive the same from
the *_addr that were passed in. Hence simplify and use BPF_MOD_{CALL,JUMP}
as types which also allows to clean up call-sites.
In addition to that, __bpf_arch_text_poke() currently verifies that text
matches expected old_insn before we invoke text_poke_bp(). Also add a check
on new_insn and skip rewrite if it already matches. Reason why this is rather
useful is that it avoids making any special casing in prog_array_map_poke_run()
when old and new prog were NULL and has the benefit that also for this case
we perform a check on text whether it really matches our expectations.
Suggested-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/fcb00a2b0b288d6c73de4ef58116a821c8fe8f2f.1574555798.git.daniel@iogearbox.net
Add initial code emission for *direct* jumps for tail call maps in
order to avoid the retpoline overhead from a493a87f38 ("bpf, x64:
implement retpoline for tail call") for situations that allow for
it, meaning, for known constant keys at verification time which are
used as index into the tail call map. In case of Cilium which makes
heavy use of tail calls, constant keys are used in the vast majority,
only for a single occurrence we use a dynamic key.
High level outline is that if the target prog is NULL in the map, we
emit a 5-byte nop for the fall-through case and if not, we emit a
5-byte direct relative jmp to the target bpf_func + skipped prologue
offset. Later during runtime, we patch these 5-byte nop/jmps upon
tail call map update or deletions dynamically. Note that on x86-64
the direct jmp works as we reuse the same stack frame and skip
prologue (as opposed to some other JIT implementations).
One of the issues is that the tail call map slots can change at any
given time even during JITing. Therefore, we have two passes: i) emit
nops for all patchable locations during main JITing phase until we
declare prog->jited = 1 eventually. At this point the image is stable,
not public yet and with all jmps disabled. While JITing, we collect
additional info like poke->ip in order to remember the patch location
for later modifications. In ii) bpf_tail_call_direct_fixup() walks
over the progs poke_tab, locks the tail call maps poke_mutex to
prevent from parallel updates and patches in the right locations via
__bpf_arch_text_poke(). Note, the main bpf_arch_text_poke() cannot
be used at this point since we're not yet exposed to kallsyms. For
the update we use plain memcpy() since the image is not public and
still in read-write mode. After patching, we activate that poke entry
through poke->ip_stable. Meaning, at this point any tail call map
updates/deletions are not going to ignore that poke entry anymore.
Then, bpf_arch_text_poke() might still occur on the read-write image
until we finally locked it as read-only. Both modifications on the
given image are under text_mutex to avoid interference with each
other when update requests come in in parallel for different tail
call maps (current one we have locked in JIT and different one where
poke->ip_stable was already set).
Example prog:
# ./bpftool p d x i 1655
0: (b7) r3 = 0
1: (18) r2 = map[id:526]
3: (85) call bpf_tail_call#12
4: (b7) r0 = 1
5: (95) exit
Before:
# ./bpftool p d j i 1655
0xffffffffc076e55c:
0: nopl 0x0(%rax,%rax,1)
5: push %rbp
6: mov %rsp,%rbp
9: sub $0x200,%rsp
10: push %rbx
11: push %r13
13: push %r14
15: push %r15
17: pushq $0x0 _
19: xor %edx,%edx |_ index (arg 3)
1b: movabs $0xffff88d95cc82600,%rsi |_ map (arg 2)
25: mov %edx,%edx | index >= array->map.max_entries
27: cmp %edx,0x24(%rsi) |
2a: jbe 0x0000000000000066 |_
2c: mov -0x224(%rbp),%eax | tail call limit check
32: cmp $0x20,%eax |
35: ja 0x0000000000000066 |
37: add $0x1,%eax |
3a: mov %eax,-0x224(%rbp) |_
40: mov 0xd0(%rsi,%rdx,8),%rax |_ prog = array->ptrs[index]
48: test %rax,%rax | prog == NULL check
4b: je 0x0000000000000066 |_
4d: mov 0x30(%rax),%rax | goto *(prog->bpf_func + prologue_size)
51: add $0x19,%rax |
55: callq 0x0000000000000061 | retpoline for indirect jump
5a: pause |
5c: lfence |
5f: jmp 0x000000000000005a |
61: mov %rax,(%rsp) |
65: retq |_
66: mov $0x1,%eax
6b: pop %rbx
6c: pop %r15
6e: pop %r14
70: pop %r13
72: pop %rbx
73: leaveq
74: retq
After; state after JIT:
# ./bpftool p d j i 1655
0xffffffffc08e8930:
0: nopl 0x0(%rax,%rax,1)
5: push %rbp
6: mov %rsp,%rbp
9: sub $0x200,%rsp
10: push %rbx
11: push %r13
13: push %r14
15: push %r15
17: pushq $0x0 _
19: xor %edx,%edx |_ index (arg 3)
1b: movabs $0xffff9d8afd74c000,%rsi |_ map (arg 2)
25: mov -0x224(%rbp),%eax | tail call limit check
2b: cmp $0x20,%eax |
2e: ja 0x000000000000003e |
30: add $0x1,%eax |
33: mov %eax,-0x224(%rbp) |_
39: jmpq 0xfffffffffffd1785 |_ [direct] goto *(prog->bpf_func + prologue_size)
3e: mov $0x1,%eax
43: pop %rbx
44: pop %r15
46: pop %r14
48: pop %r13
4a: pop %rbx
4b: leaveq
4c: retq
After; state after map update (target prog):
# ./bpftool p d j i 1655
0xffffffffc08e8930:
0: nopl 0x0(%rax,%rax,1)
5: push %rbp
6: mov %rsp,%rbp
9: sub $0x200,%rsp
10: push %rbx
11: push %r13
13: push %r14
15: push %r15
17: pushq $0x0
19: xor %edx,%edx
1b: movabs $0xffff9d8afd74c000,%rsi
25: mov -0x224(%rbp),%eax
2b: cmp $0x20,%eax .
2e: ja 0x000000000000003e .
30: add $0x1,%eax .
33: mov %eax,-0x224(%rbp) |_
39: jmpq 0xffffffffffb09f55 |_ goto *(prog->bpf_func + prologue_size)
3e: mov $0x1,%eax
43: pop %rbx
44: pop %r15
46: pop %r14
48: pop %r13
4a: pop %rbx
4b: leaveq
4c: retq
After; state after map update (no prog):
# ./bpftool p d j i 1655
0xffffffffc08e8930:
0: nopl 0x0(%rax,%rax,1)
5: push %rbp
6: mov %rsp,%rbp
9: sub $0x200,%rsp
10: push %rbx
11: push %r13
13: push %r14
15: push %r15
17: pushq $0x0
19: xor %edx,%edx
1b: movabs $0xffff9d8afd74c000,%rsi
25: mov -0x224(%rbp),%eax
2b: cmp $0x20,%eax .
2e: ja 0x000000000000003e .
30: add $0x1,%eax .
33: mov %eax,-0x224(%rbp) |_
39: nopl 0x0(%rax,%rax,1) |_ fall-through nop
3e: mov $0x1,%eax
43: pop %rbx
44: pop %r15
46: pop %r14
48: pop %r13
4a: pop %rbx
4b: leaveq
4c: retq
Nice bonus is that this also shrinks the code emission quite a bit
for every tail call invocation.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/6ada4c1c9d35eeb5f4ecfab94593dafa6b5c4b09.1574452833.git.daniel@iogearbox.net
Add BPF_MOD_{NOP_TO_JUMP,JUMP_TO_JUMP,JUMP_TO_NOP} patching for x86
JIT in order to be able to patch direct jumps or nop them out. We need
this facility in order to patch tail call jumps and in later work also
BPF static keys.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/aa4784196a8e5e985af4b30a4fe5336bce6e9643.1574452833.git.daniel@iogearbox.net
Allow FENTRY/FEXIT BPF programs to attach to other BPF programs of any type
including their subprograms. This feature allows snooping on input and output
packets in XDP, TC programs including their return values. In order to do that
the verifier needs to track types not only of vmlinux, but types of other BPF
programs as well. The verifier also needs to translate uapi/linux/bpf.h types
used by networking programs into kernel internal BTF types used by FENTRY/FEXIT
BPF programs. In some cases LLVM optimizations can remove arguments from BPF
subprograms without adjusting BTF info that LLVM backend knows. When BTF info
disagrees with actual types that the verifiers sees the BPF trampoline has to
fallback to conservative and treat all arguments as u64. The FENTRY/FEXIT
program can still attach to such subprograms, but it won't be able to recognize
pointer types like 'struct sk_buff *' and it won't be able to pass them to
bpf_skb_output() for dumping packets to user space. The FENTRY/FEXIT program
would need to use bpf_probe_read_kernel() instead.
The BPF_PROG_LOAD command is extended with attach_prog_fd field. When it's set
to zero the attach_btf_id is one vmlinux BTF type ids. When attach_prog_fd
points to previously loaded BPF program the attach_btf_id is BTF type id of
main function or one of its subprograms.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20191114185720.1641606-18-ast@kernel.org
BPF trampoline can be made to work with existing 5 bytes of BPF program
prologue, but let's add 5 bytes of NOPs to the beginning of every JITed BPF
program to make BPF trampoline job easier. They can be removed in the future.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20191114185720.1641606-14-ast@kernel.org
Introduce BPF trampoline concept to allow kernel code to call into BPF programs
with practically zero overhead. The trampoline generation logic is
architecture dependent. It's converting native calling convention into BPF
calling convention. BPF ISA is 64-bit (even on 32-bit architectures). The
registers R1 to R5 are used to pass arguments into BPF functions. The main BPF
program accepts only single argument "ctx" in R1. Whereas CPU native calling
convention is different. x86-64 is passing first 6 arguments in registers
and the rest on the stack. x86-32 is passing first 3 arguments in registers.
sparc64 is passing first 6 in registers. And so on.
The trampolines between BPF and kernel already exist. BPF_CALL_x macros in
include/linux/filter.h statically compile trampolines from BPF into kernel
helpers. They convert up to five u64 arguments into kernel C pointers and
integers. On 64-bit architectures this BPF_to_kernel trampolines are nops. On
32-bit architecture they're meaningful.
The opposite job kernel_to_BPF trampolines is done by CAST_TO_U64 macros and
__bpf_trace_##call() shim functions in include/trace/bpf_probe.h. They convert
kernel function arguments into array of u64s that BPF program consumes via
R1=ctx pointer.
This patch set is doing the same job as __bpf_trace_##call() static
trampolines, but dynamically for any kernel function. There are ~22k global
kernel functions that are attachable via nop at function entry. The function
arguments and types are described in BTF. The job of btf_distill_func_proto()
function is to extract useful information from BTF into "function model" that
architecture dependent trampoline generators will use to generate assembly code
to cast kernel function arguments into array of u64s. For example the kernel
function eth_type_trans has two pointers. They will be casted to u64 and stored
into stack of generated trampoline. The pointer to that stack space will be
passed into BPF program in R1. On x86-64 such generated trampoline will consume
16 bytes of stack and two stores of %rdi and %rsi into stack. The verifier will
make sure that only two u64 are accessed read-only by BPF program. The verifier
will also recognize the precise type of the pointers being accessed and will
not allow typecasting of the pointer to a different type within BPF program.
The tracing use case in the datacenter demonstrated that certain key kernel
functions have (like tcp_retransmit_skb) have 2 or more kprobes that are always
active. Other functions have both kprobe and kretprobe. So it is essential to
keep both kernel code and BPF programs executing at maximum speed. Hence
generated BPF trampoline is re-generated every time new program is attached or
detached to maintain maximum performance.
To avoid the high cost of retpoline the attached BPF programs are called
directly. __bpf_prog_enter/exit() are used to support per-program execution
stats. In the future this logic will be optimized further by adding support
for bpf_stats_enabled_key inside generated assembly code. Introduction of
preemptible and sleepable BPF programs will completely remove the need to call
to __bpf_prog_enter/exit().
Detach of a BPF program from the trampoline should not fail. To avoid memory
allocation in detach path the half of the page is used as a reserve and flipped
after each attach/detach. 2k bytes is enough to call 40+ BPF programs directly
which is enough for BPF tracing use cases. This limit can be increased in the
future.
BPF_TRACE_FENTRY programs have access to raw kernel function arguments while
BPF_TRACE_FEXIT programs have access to kernel return value as well. Often
kprobe BPF program remembers function arguments in a map while kretprobe
fetches arguments from a map and analyzes them together with return value.
BPF_TRACE_FEXIT accelerates this typical use case.
Recursion prevention for kprobe BPF programs is done via per-cpu
bpf_prog_active counter. In practice that turned out to be a mistake. It
caused programs to randomly skip execution. The tracing tools missed results
they were looking for. Hence BPF trampoline doesn't provide builtin recursion
prevention. It's a job of BPF program itself and will be addressed in the
follow up patches.
BPF trampoline is intended to be used beyond tracing and fentry/fexit use cases
in the future. For example to remove retpoline cost from XDP programs.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20191114185720.1641606-5-ast@kernel.org
Add bpf_arch_text_poke() helper that is used by BPF trampoline logic to patch
nops/calls in kernel text into calls into BPF trampoline and to patch
calls/nops inside BPF programs too.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20191114185720.1641606-4-ast@kernel.org
Refactor x86 JITing of LDX, STX, CALL instructions into separate helper
functions. No functional changes in LDX and STX helpers. There is a minor
change in CALL helper. It will populate target address correctly on the first
pass of JIT instead of second pass. That won't reduce total number of JIT
passes though.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20191114185720.1641606-3-ast@kernel.org
Pointer to BTF object is a pointer to kernel object or NULL.
Such pointers can only be used by BPF_LDX instructions.
The verifier changed their opcode from LDX|MEM|size
to LDX|PROBE_MEM|size to make JITing easier.
The number of entries in extable is the number of BPF_LDX insns
that access kernel memory via "pointer to BTF type".
Only these load instructions can fault.
Since x86 extable is relative it has to be allocated in the same
memory region as JITed code.
Allocate it prior to last pass of JITing and let the last pass populate it.
Pointer to extable in bpf_prog_aux is necessary to make page fault
handling fast.
Page fault handling is done in two steps:
1. bpf_prog_kallsyms_find() finds BPF program that page faulted.
It's done by walking rb tree.
2. then extable for given bpf program is binary searched.
This process is similar to how page faulting is done for kernel modules.
The exception handler skips over faulting x86 instruction and
initializes destination register with zero. This mimics exact
behavior of bpf_probe_read (when probe_kernel_read faults dest is zeroed).
JITs for other architectures can add support in similar way.
Until then they will reject unknown opcode and fallback to interpreter.
Since extable should be aligned and placed near JITed code
make bpf_jit_binary_alloc() return 4 byte aligned image offset,
so that extable aligning formula in bpf_int_jit_compile() doesn't need
to rely on internal implementation of bpf_jit_binary_alloc().
On x86 gcc defaults to 16-byte alignment for regular kernel functions
due to better performance. JITed code may be aligned to 16 in the future,
but it will use 4 in the meantime.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20191016032505.2089704-10-ast@kernel.org
Replace 'cmp reg, 0' with 'test reg, reg' for comparisons against
zero. Saves 1 byte of instruction encoding per occurrence. The flag
results of test 'reg, reg' are identical to 'cmp reg, 0' in all
cases except for AF which we don't use/care about. In terms of
macro-fusibility in combination with a subsequent conditional jump
instruction, both have the same properties for the jumps used in
the JIT translation. For example, same JITed Cilium program can
shrink a bit from e.g. 12,455 to 12,317 bytes as tests with 0 are
used quite frequently.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Introduction of bounded loops exposed old bug in x64 JIT.
JIT maintains the array of offsets to the end of all instructions to
compute jmp offsets.
addrs[0] - offset of the end of the 1st insn (that includes prologue).
addrs[1] - offset of the end of the 2nd insn.
JIT didn't keep the offset of the beginning of the 1st insn,
since classic BPF didn't have backward jumps and valid extended BPF
couldn't have a branch to 1st insn, because it didn't allow loops.
With bounded loops it's possible to construct a valid program that
jumps backwards to the 1st insn.
Fix JIT by computing:
addrs[0] - offset of the end of prologue == start of the 1st insn.
addrs[1] - offset of the end of 1st insn.
v1->v2:
- Yonghong noticed a bug in jit linfo.
Fix it by passing 'addrs + 1' to bpf_prog_fill_jited_linfo(),
since it expects insn_to_jit_off array to be offsets to last byte.
Reported-by: syzbot+35101610ff3e83119b1b@syzkaller.appspotmail.com
Fixes: 2589726d12 ("bpf: introduce bounded loops")
Fixes: 0a14842f5a ("net: filter: Just In Time compiler for x86-64")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Daniel Borkmann says:
====================
pull-request: bpf 2019-07-03
The following pull-request contains BPF updates for your *net* tree.
The main changes are:
1) Fix the interpreter to properly handle BPF_ALU32 | BPF_ARSH
on BE architectures, from Jiong.
2) Fix several bugs in the x32 BPF JIT for handling shifts by 0,
from Luke and Xi.
3) Fix NULL pointer deref in btf_type_is_resolve_source_only(),
from Stanislav.
4) Properly handle the check that forwarding is enabled on the device
in bpf_ipv6_fib_lookup() helper code, from Anton.
5) Fix UAPI bpf_prog_info fields alignment for archs that have 16 bit
alignment such as m68k, from Baruch.
6) Fix kernel hanging in unregister_netdevice loop while unregistering
device bound to XDP socket, from Ilya.
7) Properly terminate tail update in xskq_produce_flush_desc(), from Nathan.
8) Fix broken always_inline handling in test_lwt_seg6local, from Jiri.
9) Fix bpftool to use correct argument in cgroup errors, from Jakub.
10) Fix detaching dummy prog in XDP redirect sample code, from Prashant.
11) Add Jonathan to AF_XDP reviewers, from Björn.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
The current x32 BPF JIT does not correctly compile shift operations when
the immediate shift amount is 0. The expected behavior is for this to
be a no-op.
The following program demonstrates the bug. The expexceted result is 1,
but the current JITed code returns 2.
r0 = 1
r1 = 1
r1 <<= 0
if r1 == 1 goto end
r0 = 2
end:
exit
This patch simplifies the code and fixes the bug.
Fixes: 03f5781be2 ("bpf, x86_32: add eBPF JIT compiler for ia32")
Co-developed-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
The current x32 BPF JIT for shift operations is not correct when the
shift amount in a register is 0. The expected behavior is a no-op, whereas
the current implementation changes bits in the destination register.
The following example demonstrates the bug. The expected result of this
program is 1, but the current JITed code returns 2.
r0 = 1
r1 = 1
r2 = 0
r1 <<= r2
if r1 == 1 goto end
r0 = 2
end:
exit
The bug is caused by an incorrect assumption by the JIT that a shift by
32 clear the register. On x32 however, shifts use the lower 5 bits of
the source, making a shift by 32 equivalent to a shift by 0.
This patch fixes the bug using double-precision shifts, which also
simplifies the code.
Fixes: 03f5781be2 ("bpf, x86_32: add eBPF JIT compiler for ia32")
Co-developed-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Pull networking fixes from David Miller:
"Lots of bug fixes here:
1) Out of bounds access in __bpf_skc_lookup, from Lorenz Bauer.
2) Fix rate reporting in cfg80211_calculate_bitrate_he(), from John
Crispin.
3) Use after free in psock backlog workqueue, from John Fastabend.
4) Fix source port matching in fdb peer flow rule of mlx5, from Raed
Salem.
5) Use atomic_inc_not_zero() in fl6_sock_lookup(), from Eric Dumazet.
6) Network header needs to be set for packet redirect in nfp, from
John Hurley.
7) Fix udp zerocopy refcnt, from Willem de Bruijn.
8) Don't assume linear buffers in vxlan and geneve error handlers,
from Stefano Brivio.
9) Fix TOS matching in mlxsw, from Jiri Pirko.
10) More SCTP cookie memory leak fixes, from Neil Horman.
11) Fix VLAN filtering in rtl8366, from Linus Walluij.
12) Various TCP SACK payload size and fragmentation memory limit fixes
from Eric Dumazet.
13) Use after free in pneigh_get_next(), also from Eric Dumazet.
14) LAPB control block leak fix from Jeremy Sowden"
* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net: (145 commits)
lapb: fixed leak of control-blocks.
tipc: purge deferredq list for each grp member in tipc_group_delete
ax25: fix inconsistent lock state in ax25_destroy_timer
neigh: fix use-after-free read in pneigh_get_next
tcp: fix compile error if !CONFIG_SYSCTL
hv_sock: Suppress bogus "may be used uninitialized" warnings
be2net: Fix number of Rx queues used for flow hashing
net: handle 802.1P vlan 0 packets properly
tcp: enforce tcp_min_snd_mss in tcp_mtu_probing()
tcp: add tcp_min_snd_mss sysctl
tcp: tcp_fragment() should apply sane memory limits
tcp: limit payload size of sacked skbs
Revert "net: phylink: set the autoneg state in phylink_phy_change"
bpf: fix nested bpf tracepoints with per-cpu data
bpf: Fix out of bounds memory access in bpf_sk_storage
vsock/virtio: set SOCK_DONE on peer shutdown
net: dsa: rtl8366: Fix up VLAN filtering
net: phylink: set the autoneg state in phylink_phy_change
net: add high_order_alloc_disable sysctl/static key
tcp: add tcp_tx_skb_cache sysctl
...
Since commit 177366bf7c the %rbp stopped pointing to %rbp of the
previous stack frame. That broke frame pointer based stack unwinding.
This commit is a partial revert of it.
Note that the location of tail_call_cnt is fixed, since the verifier
enforces MAX_BPF_STACK stack size for programs with tail calls.
Fixes: 177366bf7c ("bpf: change x86 JITed program stack layout")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Brendan Jackman