From 01bc3b6db18d6e0a2e93c37885996bf339bfe337 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Wed, 3 Dec 2025 19:32:16 -0800 Subject: [PATCH] x86/unwind/orc: Support reliable unwinding through BPF stack frames BPF JIT programs and trampolines use a frame pointer, so the current ORC unwinder strategy of falling back to frame pointers (when an ORC entry is missing) usually works in practice when unwinding through BPF JIT stack frames. However, that frame pointer fallback is just a guess, so the unwind gets marked unreliable for live patching, which can cause livepatch transition stalls. Make the common case reliable by calling the bpf_has_frame_pointer() helper to detect the valid frame pointer region of BPF JIT programs and trampolines. Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder") Reported-by: Andrey Grodzovsky Closes: https://lore.kernel.org/0e555733-c670-4e84-b2e6-abb8b84ade38@crowdstrike.com Acked-by: Song Liu Acked-and-tested-by: Andrey Grodzovsky Signed-off-by: Josh Poimboeuf Link: https://lore.kernel.org/r/a18505975662328c8ffb1090dded890c6f8c1004.1764818927.git.jpoimboe@kernel.org Signed-off-by: Alexei Starovoitov Reviewed-by: Jiri Olsa --- arch/x86/kernel/unwind_orc.c | 39 +++++++++++++++++++++++++----------- 1 file changed, 27 insertions(+), 12 deletions(-) diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c index 977ee75e047c..f610fde2d5c4 100644 --- a/arch/x86/kernel/unwind_orc.c +++ b/arch/x86/kernel/unwind_orc.c @@ -2,6 +2,7 @@ #include #include #include +#include #include #include #include @@ -172,6 +173,25 @@ static struct orc_entry *orc_ftrace_find(unsigned long ip) } #endif +/* Fake frame pointer entry -- used as a fallback for generated code */ +static struct orc_entry orc_fp_entry = { + .type = ORC_TYPE_CALL, + .sp_reg = ORC_REG_BP, + .sp_offset = 16, + .bp_reg = ORC_REG_PREV_SP, + .bp_offset = -16, +}; + +static struct orc_entry *orc_bpf_find(unsigned long ip) +{ +#ifdef CONFIG_BPF_JIT + if (bpf_has_frame_pointer(ip)) + return &orc_fp_entry; +#endif + + return NULL; +} + /* * If we crash with IP==0, the last successfully executed instruction * was probably an indirect function call with a NULL function pointer, @@ -186,15 +206,6 @@ static struct orc_entry null_orc_entry = { .type = ORC_TYPE_CALL }; -/* Fake frame pointer entry -- used as a fallback for generated code */ -static struct orc_entry orc_fp_entry = { - .type = ORC_TYPE_CALL, - .sp_reg = ORC_REG_BP, - .sp_offset = 16, - .bp_reg = ORC_REG_PREV_SP, - .bp_offset = -16, -}; - static struct orc_entry *orc_find(unsigned long ip) { static struct orc_entry *orc; @@ -238,6 +249,11 @@ static struct orc_entry *orc_find(unsigned long ip) if (orc) return orc; + /* BPF lookup: */ + orc = orc_bpf_find(ip); + if (orc) + return orc; + return orc_ftrace_find(ip); } @@ -495,9 +511,8 @@ bool unwind_next_frame(struct unwind_state *state) if (!orc) { /* * As a fallback, try to assume this code uses a frame pointer. - * This is useful for generated code, like BPF, which ORC - * doesn't know about. This is just a guess, so the rest of - * the unwind is no longer considered reliable. + * This is just a guess, so the rest of the unwind is no longer + * considered reliable. */ orc = &orc_fp_entry; state->error = true; -- 2.47.3