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bpf: Handle return value of BPF_PROG_TYPE_STRUCT_OPS prog 

Currently if a function ptr in struct_ops has a return value, its
caller will get a random return value from it, because the return
value of related BPF_PROG_TYPE_STRUCT_OPS prog is just dropped.

So adding a new flag BPF_TRAMP_F_RET_FENTRY_RET to tell bpf trampoline
to save and return the return value of struct_ops prog if ret_size of
the function ptr is greater than 0. Also restricting the flag to be
used alone.

Fixes: 85d33df357 ("bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210914023351.3664499-1-houtao1@huawei.com
This commit is contained in:
Hou Tao 2021-09-14 10:33:51 +08:00 committed by Alexei Starovoitov
parent d198b27762
commit 356ed64991
3 changed files with 47 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
arch/x86/net/bpf_jit_comp.c
View File

@ -1744,7 +1744,7 @@ static void restore_regs(const struct btf_func_model *m, u8 **prog, int nr_args,
}
static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
struct bpf_prog *p, int stack_size, bool mod_ret)
struct bpf_prog *p, int stack_size, bool save_ret)
{
u8 *prog = *pprog;
u8 *jmp_insn;
@ -1777,11 +1777,15 @@ static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
if (emit_call(&prog, p->bpf_func, prog))
return -EINVAL;
/* BPF_TRAMP_MODIFY_RETURN trampolines can modify the return
/*
* BPF_TRAMP_MODIFY_RETURN trampolines can modify the return
* of the previous call which is then passed on the stack to
* the next BPF program.
*
* BPF_TRAMP_FENTRY trampoline may need to return the return
* value of BPF_PROG_TYPE_STRUCT_OPS prog.
*/
if (mod_ret)
if (save_ret)
emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8);
/* replace 2 nops with JE insn, since jmp target is known */
@ -1828,13 +1832,15 @@ static int emit_cond_near_jump(u8 **pprog, void *func, void *ip, u8 jmp_cond)
}
static int invoke_bpf(const struct btf_func_model *m, u8 **pprog,
struct bpf_tramp_progs *tp, int stack_size)
struct bpf_tramp_progs *tp, int stack_size,
bool save_ret)
{
int i;
u8 *prog = *pprog;
for (i = 0; i < tp->nr_progs; i++) {
if (invoke_bpf_prog(m, &prog, tp->progs[i], stack_size, false))
if (invoke_bpf_prog(m, &prog, tp->progs[i], stack_size,
save_ret))
return -EINVAL;
}
*pprog = prog;
@ -1877,6 +1883,23 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog,
return 0;
}
static bool is_valid_bpf_tramp_flags(unsigned int flags)
{
if ((flags & BPF_TRAMP_F_RESTORE_REGS) &&
(flags & BPF_TRAMP_F_SKIP_FRAME))
return false;
/*
* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,
* and it must be used alone.
*/
if ((flags & BPF_TRAMP_F_RET_FENTRY_RET) &&
(flags & ~BPF_TRAMP_F_RET_FENTRY_RET))
return false;
return true;
}
/* Example:
* __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev);
* its 'struct btf_func_model' will be nr_args=2
@ -1949,17 +1972,19 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
struct bpf_tramp_progs *fmod_ret = &tprogs[BPF_TRAMP_MODIFY_RETURN];
u8 **branches = NULL;
u8 *prog;
bool save_ret;
/* x86-64 supports up to 6 arguments. 7+ can be added in the future */
if (nr_args > 6)
return -ENOTSUPP;
if ((flags & BPF_TRAMP_F_RESTORE_REGS) &&
(flags & BPF_TRAMP_F_SKIP_FRAME))
if (!is_valid_bpf_tramp_flags(flags))
return -EINVAL;
if (flags & BPF_TRAMP_F_CALL_ORIG)
stack_size += 8; /* room for return value of orig_call */
/* room for return value of orig_call or fentry prog */
save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
if (save_ret)
stack_size += 8;
if (flags & BPF_TRAMP_F_IP_ARG)
stack_size += 8; /* room for IP address argument */
@ -2005,7 +2030,8 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
}
if (fentry->nr_progs)
if (invoke_bpf(m, &prog, fentry, stack_size))
if (invoke_bpf(m, &prog, fentry, stack_size,
flags & BPF_TRAMP_F_RET_FENTRY_RET))
return -EINVAL;
if (fmod_ret->nr_progs) {
@ -2052,7 +2078,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
}
if (fexit->nr_progs)
if (invoke_bpf(m, &prog, fexit, stack_size)) {
if (invoke_bpf(m, &prog, fexit, stack_size, false)) {
ret = -EINVAL;
goto cleanup;
}
@ -2072,9 +2098,10 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
ret = -EINVAL;
goto cleanup;
}
/* restore original return value back into RAX */
emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, -8);
}
/* restore return value of orig_call or fentry prog back into RAX */
if (save_ret)
emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, -8);
EMIT1(0x5B); /* pop rbx */
EMIT1(0xC9); /* leave */

3
include/linux/bpf.h
View File

@ -578,11 +578,12 @@ struct btf_func_model {
* programs only. Should not be used with normal calls and indirect calls.
*/
#define BPF_TRAMP_F_SKIP_FRAME BIT(2)
/* Store IP address of the caller on the trampoline stack,
* so it's available for trampoline's programs.
*/
#define BPF_TRAMP_F_IP_ARG BIT(3)
/* Return the return value of fentry prog. Only used by bpf_struct_ops. */
#define BPF_TRAMP_F_RET_FENTRY_RET BIT(4)
/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
* bytes on x86. Pick a number to fit into BPF_IMAGE_SIZE / 2

7
kernel/bpf/bpf_struct_ops.c
View File

@ -368,6 +368,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
const struct btf_type *mtype, *ptype;
struct bpf_prog *prog;
u32 moff;
u32 flags;
moff = btf_member_bit_offset(t, member) / 8;
ptype = btf_type_resolve_ptr(btf_vmlinux, member->type, NULL);
@ -431,10 +432,12 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
tprogs[BPF_TRAMP_FENTRY].progs[0] = prog;
tprogs[BPF_TRAMP_FENTRY].nr_progs = 1;
flags = st_ops->func_models[i].ret_size > 0 ?
BPF_TRAMP_F_RET_FENTRY_RET : 0;
err = arch_prepare_bpf_trampoline(NULL, image,
st_map->image + PAGE_SIZE,
&st_ops->func_models[i], 0,
tprogs, NULL);
&st_ops->func_models[i],
flags, tprogs, NULL);
if (err < 0)
goto reset_unlock;