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resolve_btfids: Enforce consistent kfunc flags across BTF ID sets

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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 <ihor.solodrai@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260722233518.778854-9-ihor.solodrai@linux.dev
This commit is contained in:
Ihor Solodrai
2026-07-22 16:35:18 -07:00
committed by Andrii Nakryiko
parent f9f60d41ba
commit 140a3479ef
1 changed files with 13 additions and 4 deletions
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17
tools/bpf/resolve_btfids/main.c
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@@ -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));