From 9a6df65d5c6a9947ddab4e563e329720f44b8747 Mon Sep 17 00:00:00 2001 From: Tiezhu Yang Date: Wed, 8 Jul 2026 18:18:05 +0800 Subject: [PATCH] bpf: Introduce jit_required flag and remove bpf_prog_has_kfunc_call() Introduce a 'jit_required' bitfield flag in struct bpf_prog to track whether a BPF program strictly requires the JIT compiler to run. This prevents a dangerous runtime fallback to the interpreter for features that are only implemented in the JIT compiler. Currently, bpf_prog_has_kfunc_call() is used only for kernel function calls, replace the kfunc-specific helper with the new 'jit_required' flag. This makes it easy to support other JIT-only BPF features, such as inlined helpers. Suggested-by: Alexei Starovoitov Suggested-by: KaFai Wan Suggested-by: Leon Hwang Acked-by: Leon Hwang Signed-off-by: Tiezhu Yang Signed-off-by: Eduard Zingerman --- include/linux/bpf.h | 9 ++------- kernel/bpf/core.c | 7 ++----- kernel/bpf/fixups.c | 5 ++--- kernel/bpf/verifier.c | 7 ++----- 4 files changed, 8 insertions(+), 20 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index c1a98fa36738..31181e0c2b80 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1864,8 +1864,9 @@ struct bpf_prog_aux { struct bpf_prog { u16 pages; /* Number of allocated pages */ - u16 jited:1, /* Is our filter JIT'ed? */ + u32 jited:1, /* Is our filter JIT'ed? */ jit_requested:1,/* archs need to JIT the prog */ + jit_required:1, /* program strictly requires JIT compiler */ gpl_compatible:1, /* Is filter GPL compatible? */ cb_access:1, /* Is control block accessed? */ dst_needed:1, /* Do we need dst entry? */ @@ -3169,7 +3170,6 @@ const struct bpf_func_proto *bpf_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog); void bpf_task_storage_free(struct task_struct *task); void bpf_cgrp_storage_free(struct cgroup *cgroup); -bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog); const struct btf_func_model * bpf_jit_find_kfunc_model(const struct bpf_prog *prog, const struct bpf_insn *insn); @@ -3508,11 +3508,6 @@ static inline void bpf_task_storage_free(struct task_struct *task) { } -static inline bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog) -{ - return false; -} - static inline const struct btf_func_model * bpf_jit_find_kfunc_model(const struct bpf_prog *prog, const struct bpf_insn *insn) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index f2b6e4c888af..47fe047ad30b 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -126,6 +126,7 @@ struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flag fp->aux->main_prog_aux = aux; fp->aux->prog = fp; fp->jit_requested = ebpf_jit_enabled(); + fp->jit_required = IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON); fp->blinding_requested = bpf_jit_blinding_enabled(fp); #ifdef CONFIG_CGROUP_BPF aux->cgroup_atype = CGROUP_BPF_ATTACH_TYPE_INVALID; @@ -2670,15 +2671,11 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env, struct /* In case of BPF to BPF calls, verifier did all the prep * work with regards to JITing, etc. */ - bool jit_needed = false; + bool jit_needed = fp->jit_required; if (fp->bpf_func) goto finalize; - if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || - bpf_prog_has_kfunc_call(fp)) - jit_needed = true; - if (!bpf_prog_select_interpreter(fp)) jit_needed = true; diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c index 12a8a4eb757f..02246df2f6c3 100644 --- a/kernel/bpf/fixups.c +++ b/kernel/bpf/fixups.c @@ -1378,7 +1378,6 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env) #ifndef CONFIG_BPF_JIT_ALWAYS_ON struct bpf_prog *prog = env->prog; struct bpf_insn *insn = prog->insnsi; - bool has_kfunc_call = bpf_prog_has_kfunc_call(prog); int depth; #endif int i, err = 0; @@ -1404,8 +1403,8 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env) return err; } #ifndef CONFIG_BPF_JIT_ALWAYS_ON - if (has_kfunc_call) { - verbose(env, "calling kernel functions are not allowed in non-JITed programs\n"); + if (prog->jit_required) { + verbose(env, "program requires BPF JIT compiler but it is not available\n"); return -EINVAL; } for (i = 0; i < env->subprog_cnt; i++) { diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ad8ff228c963..233472a871be 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2780,6 +2780,8 @@ int bpf_add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, u16 offset) prog_aux->kfunc_tab = tab; } + env->prog->jit_required = 1; + /* func_id == 0 is always invalid, but instead of returning an error, be * conservative and wait until the code elimination pass before returning * error, so that invalid calls that get pruned out can be in BPF programs @@ -2834,11 +2836,6 @@ int bpf_add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, u16 offset) return 0; } -bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog) -{ - return !!prog->aux->kfunc_tab; -} - static int add_subprog_and_kfunc(struct bpf_verifier_env *env) { struct bpf_subprog_info *subprog = env->subprog_info;