From 20d761cf195e8cbe4c0c423e8a8bdc353305274b Mon Sep 17 00:00:00 2001 From: Felix Fietkau Date: Wed, 10 Sep 2025 06:29:29 +0200 Subject: [PATCH] kernel: backport patch to allow bpf fallback to interpreter Deal with JIT failure more gracefully Fixes: https://github.com/openwrt/openwrt/issues/19405 Signed-off-by: Felix Fietkau --- ...ack-to-interpreter-for-programs-with.patch | 97 +++++++++++++++++++ 1 file changed, 97 insertions(+) create mode 100644 target/linux/generic/backport-6.12/630-v6.17-bpf-Allow-fall-back-to-interpreter-for-programs-with.patch diff --git a/target/linux/generic/backport-6.12/630-v6.17-bpf-Allow-fall-back-to-interpreter-for-programs-with.patch b/target/linux/generic/backport-6.12/630-v6.17-bpf-Allow-fall-back-to-interpreter-for-programs-with.patch new file mode 100644 index 0000000000..9943f84a90 --- /dev/null +++ b/target/linux/generic/backport-6.12/630-v6.17-bpf-Allow-fall-back-to-interpreter-for-programs-with.patch @@ -0,0 +1,97 @@ +From: KaFai Wan +Date: Tue, 9 Sep 2025 22:46:14 +0800 +Subject: [PATCH] bpf: Allow fall back to interpreter for programs with stack + size <= 512 + +OpenWRT users reported regression on ARMv6 devices after updating to latest +HEAD, where tcpdump filter: + +tcpdump "not ether host 3c37121a2b3c and not ether host 184ecbca2a3a \ +and not ether host 14130b4d3f47 and not ether host f0f61cf440b7 \ +and not ether host a84b4dedf471 and not ether host d022be17e1d7 \ +and not ether host 5c497967208b and not ether host 706655784d5b" + +fails with warning: "Kernel filter failed: No error information" +when using config: + # CONFIG_BPF_JIT_ALWAYS_ON is not set + CONFIG_BPF_JIT_DEFAULT_ON=y + +The issue arises because commits: +1. "bpf: Fix array bounds error with may_goto" changed default runtime to + __bpf_prog_ret0_warn when jit_requested = 1 +2. "bpf: Avoid __bpf_prog_ret0_warn when jit fails" returns error when + jit_requested = 1 but jit fails + +This change restores interpreter fallback capability for BPF programs with +stack size <= 512 bytes when jit fails. + +Reported-by: Felix Fietkau +Closes: https://lore.kernel.org/bpf/2e267b4b-0540-45d8-9310-e127bf95fc63@nbd.name/ +Fixes: 6ebc5030e0c5 ("bpf: Fix array bounds error with may_goto") +Signed-off-by: KaFai Wan +Acked-by: Eduard Zingerman +Link: https://lore.kernel.org/r/20250909144614.2991253-1-kafai.wan@linux.dev +Signed-off-by: Alexei Starovoitov +--- + +--- a/kernel/bpf/core.c ++++ b/kernel/bpf/core.c +@@ -2299,8 +2299,7 @@ static unsigned int __bpf_prog_ret0_warn + const struct bpf_insn *insn) + { + /* If this handler ever gets executed, then BPF_JIT_ALWAYS_ON +- * is not working properly, or interpreter is being used when +- * prog->jit_requested is not 0, so warn about it! ++ * is not working properly, so warn about it! + */ + WARN_ON_ONCE(1); + return 0; +@@ -2385,8 +2384,9 @@ out: + return ret; + } + +-static void bpf_prog_select_func(struct bpf_prog *fp) ++static bool bpf_prog_select_interpreter(struct bpf_prog *fp) + { ++ bool select_interpreter = false; + #ifndef CONFIG_BPF_JIT_ALWAYS_ON + u32 stack_depth = max_t(u32, fp->aux->stack_depth, 1); + u32 idx = (round_up(stack_depth, 32) / 32) - 1; +@@ -2395,15 +2395,16 @@ static void bpf_prog_select_func(struct + * But for non-JITed programs, we don't need bpf_func, so no bounds + * check needed. + */ +- if (!fp->jit_requested && +- !WARN_ON_ONCE(idx >= ARRAY_SIZE(interpreters))) { ++ if (idx < ARRAY_SIZE(interpreters)) { + fp->bpf_func = interpreters[idx]; ++ select_interpreter = true; + } else { + fp->bpf_func = __bpf_prog_ret0_warn; + } + #else + fp->bpf_func = __bpf_prog_ret0_warn; + #endif ++ return select_interpreter; + } + + /** +@@ -2422,7 +2423,7 @@ struct bpf_prog *bpf_prog_select_runtime + /* In case of BPF to BPF calls, verifier did all the prep + * work with regards to JITing, etc. + */ +- bool jit_needed = fp->jit_requested; ++ bool jit_needed = false; + + if (fp->bpf_func) + goto finalize; +@@ -2431,7 +2432,8 @@ struct bpf_prog *bpf_prog_select_runtime + bpf_prog_has_kfunc_call(fp)) + jit_needed = true; + +- bpf_prog_select_func(fp); ++ if (!bpf_prog_select_interpreter(fp)) ++ jit_needed = true; + + /* eBPF JITs can rewrite the program in case constant + * blinding is active. However, in case of error during -- 2.30.2