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bpf: Add bpf_arch_text_poke() helper 

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
This commit is contained in:
Alexei Starovoitov 2019-11-14 10:57:03 -08:00 committed by Daniel Borkmann
parent 3b2744e665
commit 5964b2000f
3 changed files with 65 additions and 0 deletions
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51
arch/x86/net/bpf_jit_comp.c
View File

@ -9,9 +9,11 @@
#include <linux/filter.h>
#include <linux/if_vlan.h>
#include <linux/bpf.h>
#include <linux/memory.h>
#include <asm/extable.h>
#include <asm/set_memory.h>
#include <asm/nospec-branch.h>
#include <asm/text-patching.h>
static u8 *emit_code(u8 *ptr, u32 bytes, unsigned int len)
{
@ -486,6 +488,55 @@ static int emit_call(u8 **pprog, void *func, void *ip)
return 0;
}
int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
void *old_addr, void *new_addr)
{
u8 old_insn[X86_CALL_SIZE] = {};
u8 new_insn[X86_CALL_SIZE] = {};
u8 *prog;
int ret;
if (!is_kernel_text((long)ip))
/* BPF trampoline in modules is not supported */
return -EINVAL;
if (old_addr) {
prog = old_insn;
ret = emit_call(&prog, old_addr, (void *)ip);
if (ret)
return ret;
}
if (new_addr) {
prog = new_insn;
ret = emit_call(&prog, new_addr, (void *)ip);
if (ret)
return ret;
}
ret = -EBUSY;
mutex_lock(&text_mutex);
switch (t) {
case BPF_MOD_NOP_TO_CALL:
if (memcmp(ip, ideal_nops[NOP_ATOMIC5], X86_CALL_SIZE))
goto out;
text_poke_bp(ip, new_insn, X86_CALL_SIZE, NULL);
break;
case BPF_MOD_CALL_TO_CALL:
if (memcmp(ip, old_insn, X86_CALL_SIZE))
goto out;
text_poke_bp(ip, new_insn, X86_CALL_SIZE, NULL);
break;
case BPF_MOD_CALL_TO_NOP:
if (memcmp(ip, old_insn, X86_CALL_SIZE))
goto out;
text_poke_bp(ip, ideal_nops[NOP_ATOMIC5], X86_CALL_SIZE, NULL);
break;
}
ret = 0;
out:
mutex_unlock(&text_mutex);
return ret;
}
static bool ex_handler_bpf(const struct exception_table_entry *x,
struct pt_regs *regs, int trapnr,
unsigned long error_code, unsigned long fault_addr)

8
include/linux/bpf.h
View File

@ -1157,4 +1157,12 @@ static inline u32 bpf_xdp_sock_convert_ctx_access(enum bpf_access_type type,
}
#endif /* CONFIG_INET */
enum bpf_text_poke_type {
BPF_MOD_NOP_TO_CALL,
BPF_MOD_CALL_TO_CALL,
BPF_MOD_CALL_TO_NOP,
};
int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
void *addr1, void *addr2);
#endif /* _LINUX_BPF_H */

6
kernel/bpf/core.c
View File

@ -2144,6 +2144,12 @@ int __weak skb_copy_bits(const struct sk_buff *skb, int offset, void *to,
return -EFAULT;
}
int __weak bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
void *addr1, void *addr2)
{
return -ENOTSUPP;
}
DEFINE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
EXPORT_SYMBOL(bpf_stats_enabled_key);