From 5edf6a1983b90371da888ca86493937ec1c8a2b5 Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Wed, 8 Dec 2021 20:32:43 +0100 Subject: [PATCH] bpf, x64: Replace some stack_size usage with offset variables 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 Signed-off-by: Jiri Olsa Signed-off-by: Alexei Starovoitov Acked-by: John Fastabend Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20211208193245.172141-4-jolsa@kernel.org --- arch/x86/net/bpf_jit_comp.c | 42 ++++++++++++++++++++++++++++-------------- 1 file changed, 28 insertions(+), 14 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 1d7b0c6..10fab8c 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -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 -- 2.7.4