From 98540a12823a016e2e1fa0db15543b22ac1fa056 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Fri, 15 May 2026 15:51:01 -0700 Subject: [PATCH] bpf: Clean up redundant stack arg checks for non-JITed programs Remove a redundant stack_arg_cnt check in __bpf_prog_select_runtime() and start the stack arg loop from index 0 in bpf_fixup_call_args(). Both changes are no-ops that simplify the code: In __bpf_prog_select_runtime(), the subprog_info[0].stack_arg_cnt check is unreachable: - when there is only a main program (no bpf-to-bpf calls), subprog_info[0].stack_arg_cnt is always 0 because the main program's arg_cnt is forced to 1 - when bpf-to-bpf calls use stack args and JIT succeeds, fp->bpf_func is set and this code is skipped - when JIT fails, bpf_fixup_call_args() rejects the program before we get to __bpf_prog_select_runtime(). In bpf_fixup_call_args(), starting the loop at i=1 skipped subprog 0, which is safe since the main program always has arg_cnt=1 and thus bpf_in_stack_arg_cnt() returns 0. Starting at i=0 removes the need to reason about this invariant. Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20260515225101.824054-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov --- kernel/bpf/core.c | 2 +- kernel/bpf/fixups.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 427a6d828e01..cdbe9fdf474f 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -2609,7 +2609,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env, struct goto finalize; if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || - bpf_prog_has_kfunc_call(fp) || (env && env->subprog_info[0].stack_arg_cnt)) + bpf_prog_has_kfunc_call(fp)) jit_needed = true; if (!bpf_prog_select_interpreter(fp)) diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c index 19056016eed8..2cec4e8cd4a0 100644 --- a/kernel/bpf/fixups.c +++ b/kernel/bpf/fixups.c @@ -1407,7 +1407,7 @@ int bpf_fixup_call_args(struct bpf_verifier_env *env) verbose(env, "calling kernel functions are not allowed in non-JITed programs\n"); return -EINVAL; } - for (i = 1; i < env->subprog_cnt; i++) { + for (i = 0; i < env->subprog_cnt; i++) { if (bpf_in_stack_arg_cnt(&env->subprog_info[i])) { verbose(env, "stack args are not supported in non-JITed programs\n"); return -EINVAL;