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bpf, x64: Replace some stack_size usage with offset variables

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As suggested by Andrii, adding variables for registers and ip
address offsets, which makes the code more clear, rather than
abusing single stack_size variable for everything.

Also describing the stack layout in the comment.

There is no function change.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211208193245.172141-4-jolsa@kernel.org
This commit is contained in:
Jiri Olsa 2021-12-08 20:32:43 +01:00 committed by Alexei Starovoitov
parent 2b070c2bc8
commit 5edf6a1983
1 changed files with 28 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
arch/x86/net/bpf_jit_comp.c
View File

@ -1941,7 +1941,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
void *orig_call)
{
int ret, i, nr_args = m->nr_args;
int stack_size = nr_args * 8;
int regs_off, ip_off, stack_size = nr_args * 8;
struct bpf_tramp_progs *fentry = &tprogs[BPF_TRAMP_FENTRY];
struct bpf_tramp_progs *fexit = &tprogs[BPF_TRAMP_FEXIT];
struct bpf_tramp_progs *fmod_ret = &tprogs[BPF_TRAMP_MODIFY_RETURN];
@ -1956,14 +1956,33 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
if (!is_valid_bpf_tramp_flags(flags))
return -EINVAL;
/* Generated trampoline stack layout:
*
* RBP + 8 [ return address ]
* RBP + 0 [ RBP ]
*
* RBP - 8 [ return value ] BPF_TRAMP_F_CALL_ORIG or
* BPF_TRAMP_F_RET_FENTRY_RET flags
*
* [ reg_argN ] always
* [ ... ]
* RBP - regs_off [ reg_arg1 ] program's ctx pointer
*
* RBP - ip_off [ traced function ] BPF_TRAMP_F_IP_ARG flag
*/
/* 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;
regs_off = stack_size;
if (flags & BPF_TRAMP_F_IP_ARG)
stack_size += 8; /* room for IP address argument */
ip_off = stack_size;
if (flags & BPF_TRAMP_F_SKIP_FRAME)
/* skip patched call instruction and point orig_call to actual
* body of the kernel function.
@ -1981,19 +2000,14 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
/* 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
* mov QWORD PTR [rbp - ip_off], 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;
emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -ip_off);
}
save_regs(m, &prog, nr_args, stack_size);
save_regs(m, &prog, nr_args, regs_off);
if (flags & BPF_TRAMP_F_CALL_ORIG) {
/* arg1: mov rdi, im */
@ -2005,7 +2019,7 @@ 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, regs_off,
flags & BPF_TRAMP_F_RET_FENTRY_RET))
return -EINVAL;
@ -2015,7 +2029,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
if (!branches)
return -ENOMEM;
if (invoke_bpf_mod_ret(m, &prog, fmod_ret, stack_size,
if (invoke_bpf_mod_ret(m, &prog, fmod_ret, regs_off,
branches)) {
ret = -EINVAL;
goto cleanup;
@ -2023,7 +2037,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
}
if (flags & BPF_TRAMP_F_CALL_ORIG) {
restore_regs(m, &prog, nr_args, stack_size);
restore_regs(m, &prog, nr_args, regs_off);
/* call original function */
if (emit_call(&prog, orig_call, prog)) {
@ -2053,13 +2067,13 @@ 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, false)) {
if (invoke_bpf(m, &prog, fexit, regs_off, false)) {
ret = -EINVAL;
goto cleanup;
}
if (flags & BPF_TRAMP_F_RESTORE_REGS)
restore_regs(m, &prog, nr_args, stack_size);
restore_regs(m, &prog, nr_args, regs_off);
/* This needs to be done regardless. If there were fmod_ret programs,
* the return value is only updated on the stack and still needs to be