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[86.27.177.88]) by smtp.gmail.com with ESMTPSA id p22-20020a1c5456000000b00389a558670fsm1446399wmi.11.2022.03.08.00.11.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Mar 2022 00:11:17 -0800 (PST) Date: Tue, 8 Mar 2022 08:11:15 +0000 From: Lee Jones To: Greg KH Cc: mst@redhat.com, jasowang@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, stable@vger.kernel.org, syzbot+adc3cb32385586bec859@syzkaller.appspotmail.com Subject: Re: [PATCH 1/1] vhost: Protect the virtqueue from being cleared whilst still in use Message-ID: References: <20220307191757.3177139-1-lee.jones@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 08 Mar 2022, Lee Jones wrote: > On Mon, 07 Mar 2022, Greg KH wrote: > > > On Mon, Mar 07, 2022 at 07:17:57PM +0000, Lee Jones wrote: > > > vhost_vsock_handle_tx_kick() already holds the mutex during its call > > > to vhost_get_vq_desc(). All we have to do here is take the same lock > > > during virtqueue clean-up and we mitigate the reported issues. > > > > > > Also WARN() as a precautionary measure. The purpose of this is to > > > capture possible future race conditions which may pop up over time. > > > > > > Link: https://syzkaller.appspot.com/bug?extid=279432d30d825e63ba00 > > > > > > Cc: > > > Reported-by: syzbot+adc3cb32385586bec859@syzkaller.appspotmail.com > > > Signed-off-by: Lee Jones > > > --- > > > drivers/vhost/vhost.c | 10 ++++++++++ > > > 1 file changed, 10 insertions(+) > > > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > index 59edb5a1ffe28..ef7e371e3e649 100644 > > > --- a/drivers/vhost/vhost.c > > > +++ b/drivers/vhost/vhost.c > > > @@ -693,6 +693,15 @@ void vhost_dev_cleanup(struct vhost_dev *dev) > > > int i; > > > > > > for (i = 0; i < dev->nvqs; ++i) { > > > + /* No workers should run here by design. However, races have > > > + * previously occurred where drivers have been unable to flush > > > + * all work properly prior to clean-up. Without a successful > > > + * flush the guest will malfunction, but avoiding host memory > > > + * corruption in those cases does seem preferable. > > > + */ > > > + WARN_ON(mutex_is_locked(&dev->vqs[i]->mutex)); > > > > So you are trading one syzbot triggered issue for another one in the > > future? :) > > > > If this ever can happen, handle it, but don't log it with a WARN_ON() as > > that will trigger the panic-on-warn boxes, as well as syzbot. Unless > > you want that to happen? > > No, Syzbot doesn't report warnings, only BUGs and memory corruption. > > > And what happens if the mutex is locked _RIGHT_ after you checked it? > > You still have a race... > > No, we miss a warning that one time. Memory is still protected. I didn't mean those "no"s to sound so negative, sorry. :) -- Lee Jones [李琼斯] Principal Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from smtp4.osuosl.org (smtp4.osuosl.org [140.211.166.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DB2AFC433FE for ; Tue, 8 Mar 2022 08:11:23 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id 979FC41743; Tue, 8 Mar 2022 08:11:23 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 4jI9ljkVbgUK; Tue, 8 Mar 2022 08:11:22 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by smtp4.osuosl.org (Postfix) with ESMTPS id 3BF8341719; Tue, 8 Mar 2022 08:11:22 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1A5E8C001D; Tue, 8 Mar 2022 08:11:22 +0000 (UTC) Received: from smtp4.osuosl.org (smtp4.osuosl.org [140.211.166.137]) by lists.linuxfoundation.org (Postfix) with ESMTP id 18544C000B for ; Tue, 8 Mar 2022 08:11:21 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id 12F254173F for ; Tue, 8 Mar 2022 08:11:21 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id o36c9cQKd-CJ for ; Tue, 8 Mar 2022 08:11:20 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.8.0 Received: from mail-wr1-x429.google.com (mail-wr1-x429.google.com [IPv6:2a00:1450:4864:20::429]) by smtp4.osuosl.org (Postfix) with ESMTPS id 1E70941719 for ; Tue, 8 Mar 2022 08:11:20 +0000 (UTC) Received: by mail-wr1-x429.google.com with SMTP id u10so25495396wra.9 for ; Tue, 08 Mar 2022 00:11:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=bUuwvQrXybXChtd344tucDAbC/YGVngRcc0ZDqCkqCM=; b=FOX5owV8RzTydaOm10xlR8P5JUbvjo/CFb/kM+h+EE4rb0970CllcVu7OwT3YZnsxM 3wwkCScMrKpT6xVdU36PV5QVUpwnWNlUmeSgoTOVJfdhW4Vbvf66w9jQXdKrukZ5wxCO mKx01a+tMEzg/o21jrzYQQwpxbzT/QycYJxfu+ezOnNif28TjumqmoZxUDrlqQmckKHd 7IqibmDYyuIugCo+VrhnhGPNf/jA6nRjHtYLD9y0lTybOcGB2GDHLhmN7qzudFV2Ajn1 zMB9KGQ/pVrEDXg4+5gMMG7rZXtPWCS2W/5JOW/hwY+QgfQylJ7+SNNm8R/MurItEKbQ zDRA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=bUuwvQrXybXChtd344tucDAbC/YGVngRcc0ZDqCkqCM=; b=5iOZEuprzV9bEgnwT1yWU7Wj1Qu5CCm+NC6J+xZ2sXneef7gfW9HHWUMgRWvpoW+Oj Qurjh+shozuXdM/9rQQxu/yhHCSDJ75k45inzvugPiXUIIMaY0iQMxdF92jaewq9iVGk P+Y7i+16Hb0Td7XhViaiy2Wj370PdP/wJGY9Ew4ySKlSzF8GFfpZllE9QnJUR/iHm4RC K5C6GgOCfVZCs+YBGtK15WqxI0m5f25GUJ3ah7CnUU/Lyb0cAJ5eiJRDpaN0qd5jzOVT bunetLECvNJ1yKtiNPo0VNgbmWpnA7PAhd3D+R8xtIh4H12OIVqHPTKJ90iXC5dwEFjS TnVw== X-Gm-Message-State: AOAM532eki3g95yfC3olSZ1tPvYHjv/8X4UoVmf4YP9MhytVfez1b8H8 zH9SniLgOLI/Vyi3KamZ7v8W1Q== X-Google-Smtp-Source: ABdhPJyhnQawWRN2eaq4CHOTm2Mk+XURsNwuQaphypHckXVzl4v3Ff4oimUI6+a7e/f2RNB++zpv0w== X-Received: by 2002:a5d:69d0:0:b0:1f1:fd05:e863 with SMTP id s16-20020a5d69d0000000b001f1fd05e863mr5423384wrw.223.1646727078277; Tue, 08 Mar 2022 00:11:18 -0800 (PST) Received: from google.com (cpc155339-bagu17-2-0-cust87.1-3.cable.virginm.net. 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