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bpf: Give vmlinux BTF init its own mutex

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bpf_get_btf_vmlinux() serializes the lazy vmlinux BTF parse with
bpf_verifier_lock, the same mutex bpf_check() holds across the whole
verification of an unprivileged program (if enabled; it's disabled
by default). The latter can potentially stall the mutex holder for
a long time (e.g. via userfaultfd), and therefore block first-time
bpf_get_btf_vmlinux() caller from any context, including privileged
program loads.

Give the vmlinux BTF initialization a dedicated btf_vmlinux_lock so
it is independent of the unprivileged verification mutex. The parse
only needs mutual exclusion against itself.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20260708211537.371874-3-daniel@iogearbox.net
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
This commit is contained in:
Daniel Borkmann
2026-07-08 23:15:35 +02:00
committed by Kumar Kartikeya Dwivedi
parent 92863e6780
commit 5e5e94d87d
2 changed files with 5 additions and 4 deletions
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2
kernel/bpf/btf.c
View File

@@ -6451,7 +6451,7 @@ struct btf *btf_parse_vmlinux(void)
if (IS_ERR(btf))
goto err_out;
/* btf_parse_vmlinux() runs under bpf_verifier_lock */
/* btf_parse_vmlinux() runs under btf_vmlinux_lock */
bpf_ctx_convert.t = btf_type_by_id(btf, bpf_ctx_convert_btf_id[0]);
err = btf_alloc_id(btf);
if (err) {

7
kernel/bpf/verifier.c
View File

@@ -324,6 +324,7 @@ static const char *btf_type_name(const struct btf *btf, u32 id)
}
static DEFINE_MUTEX(bpf_verifier_lock);
static DEFINE_MUTEX(btf_vmlinux_lock);
static DEFINE_MUTEX(bpf_percpu_ma_lock);
__printf(2, 3) static void verbose(void *private_data, const char *fmt, ...)
@@ -19563,7 +19564,7 @@ struct btf *bpf_get_btf_vmlinux(void)
struct btf *btf = smp_load_acquire(&btf_vmlinux);
if (!btf && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
mutex_lock(&bpf_verifier_lock);
mutex_lock(&btf_vmlinux_lock);
btf = btf_vmlinux;
if (!btf) {
btf = btf_parse_vmlinux();
@@ -19575,7 +19576,7 @@ struct btf *bpf_get_btf_vmlinux(void)
*/
smp_store_release(&btf_vmlinux, btf);
}
mutex_unlock(&bpf_verifier_lock);
mutex_unlock(&btf_vmlinux_lock);
}
return btf;
}
@@ -20089,7 +20090,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
bpf_get_btf_vmlinux();
/* grab the mutex to protect few globals used by verifier */
/* Serialize verification of unprivileged programs. */
if (!is_priv)
mutex_lock(&bpf_verifier_lock);