From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 C600F17BCA; Fri, 30 Jan 2026 10:23:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769768588; cv=none; b=D5PSmYpJxuta7UmpD6YyIznoRhMd/xCXy/Vy8nGT1HIoMPHjxrTb/opkxeybkhnVstflgax0rlFEmqjtiOrB0FNhKDj4luojP9spcIoYN+A7UjUPO19KNujYBumLtQkAxxByuZcq+0Ht1Y7UxaqewDPmeq4HTDbmnNXxkHvCp4g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769768588; c=relaxed/simple; bh=qMBOafVGCTH88IYyfHxlvW2KTuXT3aCn+vgg6N7/myA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=fbFc+QFaHJ383pmFwvtrL/s+DzdbBEBGrmi6vq/H4CTtxO0C/3Ng4sPuteqQdh8gBGk/Fj3d7YKP7wwPU2Yr4Zjz1p5DzfqKaE1caZjpo/KgvRIlbZHb0arWYE5o5wG1SLexrTJTOwrmu6dGWTCzIQ/nP9yEKzsRhkPtNHmHDlg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=HOYTzIPB; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="HOYTzIPB" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=BVh+chDyG+s+tV3ClqBUlFmOiGpBgy6M929kQydFBkM=; b=HOYTzIPBzwiMyej170IjZbTqF8 me4s6iWqZclaDh17c2TWDFXjgcON1PwUztlg2t9fYX9/rK/rz0n07oNETA9Dxo4Kz4ry/Qnh2jdZj DosoDy+SQIFDVUHsAq41+SJdagiPFFHo/ccd2FS8HftmZCJ7d0RHq0uqnzx5pXUyGgVo6r/Jihh0P fiqvi4xvSRCS4aRG7istDMJiXee6DxY/wXVna3aPmhfCc2lwvzysNVtYVy9GHMwqR7UdEWiPEPSWB yOBA8B/eSNWN81ALeyfqYnQHeODe16vRGuZIDT4UVmf4JtFyJD53n4nCaIfLhNmXAiSuYj51mxLYy fd/PSWCg==; Received: from 2001-1c00-8d85-5700-266e-96ff-fe07-7dcc.cable.dynamic.v6.ziggo.nl ([2001:1c00:8d85:5700:266e:96ff:fe07:7dcc] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vlleX-0000000BcRJ-1FXV; Fri, 30 Jan 2026 10:23:01 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 2C26930331F; Fri, 30 Jan 2026 11:23:00 +0100 (CET) Date: Fri, 30 Jan 2026 11:23:00 +0100 From: Peter Zijlstra To: Henry Zhang Cc: mingo@redhat.com, acme@kernel.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Henry Zhang , syzbot+2a077cb788749964cf68@syzkaller.appspotmail.com, andrii@kernel.org Subject: Re: [PATCH] perf: Fix data race in perf_event_set_bpf_handler() Message-ID: <20260130102300.GA171111@noisy.programming.kicks-ass.net> References: <20260127023618.1469937-1-zeri@umich.edu> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260127023618.1469937-1-zeri@umich.edu> On Mon, Jan 26, 2026 at 09:36:18PM -0500, Henry Zhang wrote: > KCSAN reported a data race where perf_event_set_bpf_handler() writes > event->prog while __perf_event_overflow() reads it concurrently from > interrupt context: > > BUG: KCSAN: data-race in __perf_event_overflow / __perf_event_set_bpf_prog > > write to 0xffff88811b219168 of 8 bytes by task 13065 on cpu 0: > perf_event_set_bpf_handler kernel/events/core.c:10352 [inline] > __perf_event_set_bpf_prog+0x418/0x470 kernel/events/core.c:11303 > ... > > read to 0xffff88811b219168 of 8 bytes by interrupt on cpu 1: > __perf_event_overflow+0x252/0x920 kernel/events/core.c:10410 > ... > > Annotate event->prog access with WRITE_ONCE/READ_ONCE. > > Reported-by: syzbot+2a077cb788749964cf68@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=2a077cb788749964cf68 > Signed-off-by: Henry Zhang > --- > kernel/events/core.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index a0fa488bce84..1f3ed9e87507 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -10349,7 +10349,7 @@ static inline int perf_event_set_bpf_handler(struct perf_event *event, > return -EPROTO; > } > > - event->prog = prog; > + WRITE_ONCE(event->prog, prog); > event->bpf_cookie = bpf_cookie; What about that cookie thing? The consumer seems to be a bpf function (bpf_get_attach_cookie_pe) which can equally run concurrently, no? Also, there seems to be a coherency issue here, if prog runs, it expects cookie to be present and all that. Would that not suggest something like: WRITE_ONCE(event->bpf_cookie, bpf_cookie); smp_store_release(&event->prog, prog); > return 0; > } > @@ -10407,7 +10407,9 @@ static int __perf_event_overflow(struct perf_event *event, > if (event->attr.aux_pause) > perf_event_aux_pause(event->aux_event, true); > > - if (event->prog && event->prog->type == BPF_PROG_TYPE_PERF_EVENT && > + struct bpf_prog *prog = READ_ONCE(event->prog); smp_load_acquire(&event->prog); > + > + if (prog && prog->type == BPF_PROG_TYPE_PERF_EVENT && > !bpf_overflow_handler(event, data, regs)) > goto out; > Hmm?