bpf_get_func_ip() helper function returns the address of the traced function. It relies on the IP address stored at ctx - 16 by the bpf trampoline. On 64-bit powerpc, this address is recovered from LR accounting for OOL trampoline. But the address stored here was off by 4-bytes. Ensure the address is the actual start of the traced function. Reported-by: Abhishek Dubey Fixes: d243b62b7bd3 ("powerpc64/bpf: Add support for bpf trampolines") Cc: stable@vger.kernel.org Tested-by: Venkat Rao Bagalkote Signed-off-by: Hari Bathini --- Changes in v3: - Added Tested-by tag from Venkat. - Updated comments based on suggestions from Abhishek. arch/powerpc/net/bpf_jit_comp.c | 28 +++++++++++++++++++--------- 1 file changed, 19 insertions(+), 9 deletions(-) diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index 52162e4a7f84..95f208229b09 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -785,9 +785,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im * retval_off [ return value ] * [ reg argN ] * [ ... ] - * regs_off [ reg_arg1 ] prog ctx context - * nregs_off [ args count ] - * ip_off [ traced function ] + * regs_off [ reg_arg1 ] prog_ctx + * nregs_off [ args count ] ((u64 *)prog_ctx)[-1] + * ip_off [ traced function ] ((u64 *)prog_ctx)[-2] * [ ... ] * run_ctx_off [ bpf_tramp_run_ctx ] * [ reg argN ] @@ -895,7 +895,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im bpf_trampoline_save_args(image, ctx, func_frame_offset, nr_regs, regs_off); - /* Save our return address */ + /* Save our LR/return address */ EMIT(PPC_RAW_MFLR(_R3)); if (IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE)) EMIT(PPC_RAW_STL(_R3, _R1, alt_lr_off)); @@ -903,24 +903,34 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im EMIT(PPC_RAW_STL(_R3, _R1, bpf_frame_size + PPC_LR_STKOFF)); /* - * Save ip address of the traced function. - * We could recover this from LR, but we will need to address for OOL trampoline, - * and optional GEP area. + * Derive IP address of the traced function. + * In case of CONFIG_PPC_FTRACE_OUT_OF_LINE or BPF program, LR points to the instruction + * after the 'bl' instruction in the OOL stub. Refer to ftrace_init_ool_stub() and + * bpf_arch_text_poke() for OOL stub of kernel functions and bpf programs respectively. + * Relevant stub sequence: + * + * bl + * LR (R3) => mtlr r0 + * b + * + * Recover kernel function/bpf program address from the unconditional + * branch instruction at the end of OOL stub. */ if (IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) || flags & BPF_TRAMP_F_IP_ARG) { EMIT(PPC_RAW_LWZ(_R4, _R3, 4)); EMIT(PPC_RAW_SLWI(_R4, _R4, 6)); EMIT(PPC_RAW_SRAWI(_R4, _R4, 6)); EMIT(PPC_RAW_ADD(_R3, _R3, _R4)); - EMIT(PPC_RAW_ADDI(_R3, _R3, 4)); } if (flags & BPF_TRAMP_F_IP_ARG) EMIT(PPC_RAW_STL(_R3, _R1, ip_off)); - if (IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE)) + if (IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE)) { /* Fake our LR for unwind */ + EMIT(PPC_RAW_ADDI(_R3, _R3, 4)); EMIT(PPC_RAW_STL(_R3, _R1, bpf_frame_size + PPC_LR_STKOFF)); + } /* Save function arg count -- see bpf_get_func_arg_cnt() */ EMIT(PPC_RAW_LI(_R3, nr_regs)); -- 2.53.0