From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B4EB73491C9; Sat, 12 Sep 2026 18:41:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789238520; cv=none; b=hQ+bsXUb7h/EtOHQgtXGkqVA2gXkb7b8qjXef71uVAaq9iUtisKeujC7NS5JlnFXABmfipg2lDPAGxPJi3fGtaxyCsmBG33GntpU0CntexUYoGs2crfM4Q5RjJs6qlknbufKkpldXrI5Ce9Ad3yRFG84Q/zlbyFqIKUy/hgDoSA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789238520; c=relaxed/simple; bh=wtBbPIUM1nqmB1cWCxREzx5f5psDDE2cundEa/NzLIc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=olM75kSLrmvdujiHWh2ecZG5TuA3jBy1Oo6srZ8Gm5GmdAoCOKaQuo+lk5x2QiUYs3zTrgV/VUvoue0ZDR/5JZqAlqVA1mqWRo/cLHuYQhBlimO3TkKXgoIju/bVDcAJ+f7XTwSUmQUvWG/7jBAbtt2bNvNIoSSqdonunOetmCA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ujnNDJNN; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="ujnNDJNN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 244A71F000FF; Sat, 12 Sep 2026 18:41:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789238518; bh=u1iMaUUEb9cZWLD1dvOTEXzsiiLRJ1CJBi4J0cr7jtc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ujnNDJNN7m4eNhQHxQOzq191mVH4qZ40a31IHodeIxiNyLHJAtgNzqsVw0Io2PrG8 Duo18U4NSki0r2q5mNFKFkgT664B1+b3lje9MQ/s9GEUFaV691LxfDRAERs8JCAOc4 g7tcIktimoBhxdg00eO0/COTSMcX0YXa7MyYBtd0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Daniel Borkmann , Kumar Kartikeya Dwivedi , Sasha Levin Subject: [PATCH 5.15 477/935] bpf: Fix vmlinux BTF prep race in bpf_get_btf_vmlinux Date: Sat, 12 Sep 2026 08:58:27 +0200 Message-ID: <20260912065537.765734042@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065526.833703348@linuxfoundation.org> References: <20260912065526.833703348@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Daniel Borkmann [ Upstream commit 92863e678070f57c17c868e4bfa2441a5c61ad2b ] bpf_get_btf_vmlinux() lazily parses the vmlinux BTF under the bpf_verifier_lock, but publishes the result through a plain store and re-checks it through a plain lockless load. Nothing orders the stores initializing the struct btf inside btf_parse_vmlinux() against the store publishing the pointer: On a weakly ordered arch, a concurrent first-time caller taking the lockless fast path could in principle observe the pointer before the parsed contents are visible. The mutex_unlock() does not help such a reader given it only synchronizes with a later acquisition of the same lock. Thus, publish the pointer with smp_store_release() and read it on the fast path with smp_load_acquire(). Acquire semantics are needed rather than a dependency-ordered READ_ONCE(): btf_parse_vmlinux() also populates globals outside the returned object (e.g. bpf_ctx_convert.t). An address dependency would only order accesses performed through the pointer and not cover other globals. Fixes: 8580ac9404f6 ("bpf: Process in-kernel BTF") Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20260708211537.371874-2-daniel@iogearbox.net Signed-off-by: Kumar Kartikeya Dwivedi Signed-off-by: Sasha Levin --- kernel/bpf/verifier.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8950f949377a3..4e2d49b0d1f1c 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -14040,13 +14040,25 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) struct btf *bpf_get_btf_vmlinux(void) { - if (!btf_vmlinux && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) { + /* Pairs with the smp_store_release() on the parse path below. */ + struct btf *btf = smp_load_acquire(&btf_vmlinux); + + if (!btf && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) { mutex_lock(&bpf_verifier_lock); - if (!btf_vmlinux) - btf_vmlinux = btf_parse_vmlinux(); + btf = btf_vmlinux; + if (!btf) { + btf = btf_parse_vmlinux(); + /* + * Order the parsed BTF contents and the globals the + * parse populated (e.g. bpf_ctx_convert.t) before + * the pointer publication. Pairs with the acquire + * on the lockless fast path above. + */ + smp_store_release(&btf_vmlinux, btf); + } mutex_unlock(&bpf_verifier_lock); } - return btf_vmlinux; + return btf; } int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr) -- 2.53.0