From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-161.mta1.migadu.com [95.215.58.161]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 737AE48F022 for ; Mon, 28 Sep 2026 08:51:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.161 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790585463; cv=none; b=lxX7K52lsQfzRoWWTr5Yp8nAl3MBqwZAVqemK8/ETX+3cM3F7Cs22jSGouO/5UxaWTxUP7N1P/4OHhJFt0BLSNoT1W1l7aB5+E/Wk29aOKv7pZurjUj1MvXmXH6HJRXsWSNVYBLNUqu8wTQSns6Uw1HsIM9jStuhIvORurxt+zs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790585463; c=relaxed/simple; bh=09WBzyqcOHBSt5hLHqAwbTciP1G0S+c8iry/IFi/HlI=; h=Mime-Version:Content-Type:Date:Message-Id:From:To:Cc:Subject: References:In-Reply-To; b=TzLu/WeBfOb3+N8JCgIgz4BlFIPZ5jY2R/kWFpq1YsPDih9Z2vKlopxjqNGLRO7k0ACmjML3qRi62wbyHEPx1KzBQ0zfBDes/42VcsSBmtQtwriYIKvxNdduuQQuf1VnuuKWdskzhE22Xg8i9tgPSJJAHnrDNLQ+5HQ11sEtTwo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=hlJSyJb4; arc=none smtp.client-ip=95.215.58.161 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="hlJSyJb4" X-Envelope-To: linux-kselftest@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=09WBzyqcOHBSt5hLHqAwbTciP1G0S+c8iry/IFi/HlI=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1790585459; v=1; x=1791190259; b=hlJSyJb4zyvL5tTc5B+UKJvJCZdxkTMJPLEWB4nUbp/tleH04SocnIPGb4w8yi3m5ovXyx/z NSXt9VR0s+2Xg/Os5fYU54qClXCgayhYrJKbIYjmLqn2jdYk36jdndIr87ji4R0cYdAR0U+78QB B7kA8WSWg0tewIstOzALdJoI= X-Envelope-To: linux-kselftest@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id dcca5a333ecbdbdc; Mon, 28 Sep 2026 08:50:58 +0000 X-Mizu-Trace-ID: dcca5a333ecbdbdc X-Migadu-Flow: FLOW_OUT Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 28 Sep 2026 08:50:55 +0000 Message-Id: From: "Florent Revest" To: , , , , Cc: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH bpf v5 1/3] bpf: Wait for an RCU tasks grace period before freeing trampoline progs X-Mailer: aerc 0.17.0 References: <20260926135605.1217928-2-florent.revest@linux.dev> <9d932a22ca908da9378ea281633ddb749453911ac6ae7a27a09e376f9ad02ff7@mail.kernel.org> In-Reply-To: <9d932a22ca908da9378ea281633ddb749453911ac6ae7a27a09e376f9ad02ff7@mail.kernel.org> On Sun Sep 27, 2026 at 8:41 PM UTC, wrote: > > bpf: Wait for an RCU tasks grace period before freeing trampoline progs > > > > When a prog is detached from a trampoline, it is freed after an RCU > > grace period, or an RCU tasks trace one if it is sleepable. This covers > > the tasks that are running the prog, since the prog's enter helper take= s > > the matching read lock before the prog is called. On a preemptible > > kernel, it doesn't cover a task that was preempted in the trampoline > > just before the enter helper. That task holds no lock yet, and it calls > > the prog after it was freed: > > > > BUG: KASAN: vmalloc-out-of-bounds in __bpf_prog_enter_recur+0x3a5/0x3= f0 > > Read of size 8 at addr ffffc90000055040 by task candidate/110 > > CPU: 1 UID: 0 PID: 110 Comm: candidate Not tainted 7.3.0-rc2-00014-g1= 5071f2a1263-dirty #2 PREEMPT(full) > > Call Trace: > > > > __bpf_prog_enter_recur+0x3a5/0x3f0 > > bpf_trampoline_6442509193+0x37/0xf1 > > __x64_sys_futex+0x9/0x410 > > do_syscall_64+0xb0/0x530 > > ... > > > > Wait for an RCU tasks grace period before the existing one when freeing > > a prog that was linked to a trampoline. An RCU tasks grace period only > > ends once the tasks that were preempted have run again, and > > bpf_tramp_image_put() already relies on it to free the image. It doesn'= t > > wait for tasks that sleep in the trampoline, the next commit takes care > > of those. > > > > Only progs that were linked to a trampoline can be called this way, so > > bpf_trampoline_add_prog() marks them and other progs are still freed as > > before. > > > > Fixes: e21aa341785c ("bpf: Fix fexit trampoline.") > > Is this the right Fixes: target? > > The race being closed here (a task preempted inside the trampoline image > before __bpf_prog_enter*() takes its RCU read lock, while the prog is fre= ed > after only a regular RCU or RCU tasks trace grace period) appears to pred= ate > e21aa341785c. > > In fec56f5890d9 ("bpf: Introduce BPF trampoline") bpf_trampoline_update() > switched images with no tasks RCU wait, and __bpf_prog_put_noref() freed = the > prog with a plain call_rcu(&prog->aux->rcu, __bpf_prog_put_rcu). > > Just before e21aa341785c, the synchronize_rcu_mult(call_rcu_tasks, > call_rcu_tasks_trace) in bpf_trampoline_update() ran before > arch_prepare_bpf_trampoline() rather than after the new image was install= ed, > and the total =3D=3D 0 unregister_fentry() path had no wait at all, so a = task > preempted in the old image could already reach a freed prog. > > Would Fixes: fec56f5890d9 ("bpf: Introduce BPF trampoline") be more > accurate, so that stable trees without e21aa341785c also pick this up? Th= e > follow-up 49ca60187380 in this series uses the same tag. Yeah, that seems right. It shouldn't make much of a difference for stable because both have been introduced in the same 5.10.y. I can either switch t= his if there's a v6 or a maintainer can change when applying.