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bpf, x86: Store caller's ip in trampoline stack 

Storing caller's ip in trampoline's stack. Trampoline programs
can reach the IP in (ctx - 8) address, so there's no change in
program's arguments interface.

The IP address is takes from [fp + 8], which is return address
from the initial 'call fentry' call to trampoline.

This IP address will be returned via bpf_get_func_ip helper
helper, which is added in following patches.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210714094400.396467-2-jolsa@kernel.org
This commit is contained in:
Jiri Olsa 2021-07-14 11:43:53 +02:00 committed by Alexei Starovoitov
parent 7628317192
commit 7e6f3cd89f
2 changed files with 24 additions and 0 deletions
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19
arch/x86/net/bpf_jit_comp.c
View File

@ -1951,6 +1951,9 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
if (flags & BPF_TRAMP_F_CALL_ORIG)
stack_size += 8; /* room for return value of orig_call */
if (flags & BPF_TRAMP_F_IP_ARG)
stack_size += 8; /* room for IP address argument */
if (flags & BPF_TRAMP_F_SKIP_FRAME)
/* skip patched call instruction and point orig_call to actual
* body of the kernel function.
@ -1964,6 +1967,22 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
EMIT4(0x48, 0x83, 0xEC, stack_size); /* sub rsp, stack_size */
EMIT1(0x53); /* push rbx */
if (flags & BPF_TRAMP_F_IP_ARG) {
/* Store IP address of the traced function:
* mov rax, QWORD PTR [rbp + 8]
* sub rax, X86_PATCH_SIZE
* mov QWORD PTR [rbp - stack_size], rax
*/
emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, 8);
EMIT4(0x48, 0x83, 0xe8, X86_PATCH_SIZE);
emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -stack_size);
/* Continue with stack_size for regs storage, stack will
* be correctly restored with 'leave' instruction.
*/
stack_size -= 8;
}
save_regs(m, &prog, nr_args, stack_size);
if (flags & BPF_TRAMP_F_CALL_ORIG) {

5
include/linux/bpf.h
View File

@ -579,6 +579,11 @@ struct btf_func_model {
*/
#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)
/* 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
*/