From 140a3479ef66507a7de06f4cd8bcefb86d2c640a Mon Sep 17 00:00:00 2001 From: Ihor Solodrai Date: Wed, 22 Jul 2026 16:35:18 -0700 Subject: [PATCH] resolve_btfids: Enforce consistent kfunc flags across BTF ID sets A kfunc may be listed in several BTF ID sets, which is expected because different kfuncs are available to BPF programs depending on their type. However kfunc flags across different BTF ID sets must be consistent [1]. The flags should be considered a part of the kfunc declaration, because they influence its BTF representation and verifier handling. Enforce the kfunc flag consistency in resolve_btifds by hard failing on error and blocking kernel (or module) build. [1] https://lore.kernel.org/bpf/9b2196dd-443b-4632-ae11-030cdbdc59b4@linux.dev/ Signed-off-by: Ihor Solodrai Signed-off-by: Andrii Nakryiko Reviewed-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20260722233518.778854-9-ihor.solodrai@linux.dev --- tools/bpf/resolve_btfids/main.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c index 338d0c0a8e58..85488935909d 100644 --- a/tools/bpf/resolve_btfids/main.c +++ b/tools/bpf/resolve_btfids/main.c @@ -982,17 +982,26 @@ static int push_kfunc(struct btf2btf_context *ctx, struct kfunc *kfunc) struct rb_node *parent = NULL; struct kfunc *k; - /* Dedup by BTF ID: collecting the same kfunc twice is a no-op. */ + /* + * Dedup by BTF ID: collecting the same kfunc twice is a no-op, + * UNLESS the kfunc flags are inconsistent, in which case we + * fail hard because it indicates a bug in a kfunc set declaration. + */ while (*p) { parent = *p; k = rb_entry(parent, struct kfunc, rb_node); - if (kfunc->btf_id < k->btf_id) + if (kfunc->btf_id < k->btf_id) { p = &(*p)->rb_left; - else if (kfunc->btf_id > k->btf_id) + } else if (kfunc->btf_id > k->btf_id) { p = &(*p)->rb_right; - else + } else if (k->flags == kfunc->flags) { return 0; + } else { + pr_err("ERROR: resolve_btfids: kfunc %s has inconsistent flags across BTF ID sets: 0x%x != 0x%x\n", + kfunc->name, k->flags, kfunc->flags); + return -EINVAL; + } } k = zalloc(sizeof(*k));