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 ADBBBEAC7; Tue, 14 Jul 2026 13:17:46 +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=1784035067; cv=none; b=SHJLHQTz4nlhum8mHTn5O1EtRne3DtrIR8Aza/M1kHl+pCnK3LZB3lepMBgrpvlseHiSfKVvIc+YobagcnwoteOVQE5fVlVkBH/xerOxHWs5AjQyNHXuxn4yKjEAh2Xzh8wOEDq5mFi0nAw82CIGVMx09EfSEufkdnbHdBdQAP8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784035067; c=relaxed/simple; bh=w1ZUj1749/I3WMkB1bXQWcYiLYcInm+Txyh34c/H1cM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IeyZeGuH8ZaYdlQaxQv05wMoiIxrHOSId18Mx3/nBa4JCN9SurSq+Ci2xaMgjz5px/GTllAaKQd5ihZCXsmnlxlONZZQPI378Yw4pxQU5Qwyj+MbgYwocXt0+hXr4gX3R0ZVSAOqCw8HWSCjpDMqq8rfFhrEib0+dIjrPEAyb2g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FED4vNrC; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="FED4vNrC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 887CA1F00A3A; Tue, 14 Jul 2026 13:17:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784035066; bh=XPP2myTGPA5lMKiNw+TtdOeHCWrcAC/vqmt4XlyULw4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FED4vNrCvRA+E87/OHhMTv0sfCp09VAGYZiCGXNOiE/pu8OVC+5T3j135myCIb0B+ HyytLmY+Zx+54l8JqAbasXFFpi4S5Wvw45Hyr3VUpIrati8G7aqxEqOIwPHfmZDNlM WWJIeDXiIWaWuTZ88BGzH1cfhWqwQQHEHu0p9yjTXmw/Am4wTsLlVQuzpZofqiFlW0 AD+aQnQhQCtuAJkK/rd8PGJjcdPzRLRFWEm7QIwUMLdDEDo3j0ey9lq/HkjI8UL5Wt tbhorm20fDX8meWpCOhymc5mNvLYAPYcYIUtkesKWymOv+FhcI7oF58MmI83iUWW2L bq9WyWLH+mVnA== Message-ID: <8d316b6c-41fb-4ae3-8923-3b649b92b33d@kernel.org> Date: Tue, 14 Jul 2026 15:17:42 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] virtio_balloon: fix Use-After-Free in page reporting during PM freeze To: Link Lin , Andrew Morton , Vlastimil Babka , "Michael S . Tsirkin" Cc: virtualization@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, prasin@google.com, rientjes@google.com, duenwen@google.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, Ammar Faizi , jiaqiyan@google.com, ahwilkins@google.com, Greg Thelen , Alexander Duyck , stable@vger.kernel.org References: <20260709224330.946683-1-linkl@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260709224330.946683-1-linkl@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/10/26 00:43, Link Lin wrote: > During system power management freeze (e.g. ACPI S3 suspend or S4 > hibernation), virtballoon_freeze() calls remove_common() to reset the > virtio device and delete all virtqueues via vdev->config->del_vqs(). > However, unlike virtballoon_remove(), virtballoon_freeze() fails to call > page_reporting_unregister(&vb->pr_dev_info). > > The comment in virtballoon_freeze() states: > /* > * The workqueue is already frozen by the PM core before this > * function is called. > */ > > While this comment was accurate in 2011 for balloon-internal workqueues > (such as balloon_wq, which was created with WQ_FREEZABLE and is paused > by the PM freezer), it is invalid for Free Page Reporting. > > Free Page Reporting (mm/page_reporting.c) schedules its delayed work > (prdev->work) on the global system_wq. Because system_wq lacks the > WQ_FREEZABLE flag, the PM freezer (freeze_workqueues_busy()) explicitly > skips it. Consequently, page_reporting_process() on system_wq remains > active and unfrozen throughout device suspend. > > If memory is freed into the buddy allocator or a delayed work timer > expires while the device is being frozen, page_reporting_process() fires > on system_wq and calls virtballoon_free_page_report(). This function > passes vb->reporting_vq into virtqueue_add_inbuf() / virtqueue_add_split(). > Because the virtqueues were already destroyed by del_vqs(), this results > in a Use-After-Free / General Protection Fault: > > [ 250.709271] general protection fault, probably for non-canonical address 0x7f728084daf08d5e: 0000 [#1] SMP PTI > [ 250.732967] CPU: 2 PID: 38 Comm: kworker/2:1 Not tainted 5.10.0-44-cloud-amd64 #1 Debian 5.10.257-1 > [ 250.751575] Workqueue: events page_reporting_process > [ 250.756665] RIP: 0010:virtqueue_add_split+0x233/0x4c0 [virtio_ring] > ... > [ 250.867678] virtballoon_free_page_report+0x3a/0xe0 [virtio_balloon] > [ 250.883446] page_reporting_process+0x225/0x4f0 > > (Note: The OOM Notifier and Shrinker/Free Page Hinting features suffer > from an identical lifecycle flaw and are also vulnerable to UAFs during > S4 hibernation when memory pressure spikes. This patch focuses on Free > Page Reporting, which runs periodically, to ensure clean backports to > stable kernels). > > Fix this by: > 1. Unregistering page reporting in virtballoon_freeze() prior to calling > remove_common(). This clears the RCU pr_dev_info pointer and flushes/ > cancels prdev->work on system_wq via cancel_delayed_work_sync(). > 2. Re-registering page reporting in virtballoon_restore() after the > virtqueues are re-initialized and virtio_device_ready() has been called. > 3. Unwinding virtqueue initialization via remove_common() in > virtballoon_restore() if page_reporting_register() fails. > > Fixes: 924a663f75e2 ("virtio-balloon: Reporting free page reservations") > Cc: stable@vger.kernel.org > Cc: jasowang@redhat.com > Cc: xuanzhuo@linux.alibaba.com > Cc: Ammar Faizi > Cc: jiaqiyan@google.com > Cc: ahwilkins@google.com > Cc: Greg Thelen > Cc: Alexander Duyck > Signed-off-by: Link Lin > --- > drivers/virtio/virtio_balloon.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index a1b2c3d4e5f6..45a90fb3abf8 100640 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -1055,6 +1055,9 @@ static int virtballoon_freeze(struct virtio_device *vdev) > * The workqueue is already frozen by the PM core before this > * function is called. > */ > + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) > + page_reporting_unregister(&vb->pr_dev_info); > + > remove_common(vb); > return 0; > } > > static int virtballoon_restore(struct virtio_device *vdev) > { > struct virtio_balloon *vb = vdev->priv; > int ret; > > ret = init_vqs(vdev->priv); > if (ret) > return ret; > > virtio_device_ready(vdev); > > + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) { > + ret = page_reporting_register(&vb->pr_dev_info); > + if (ret) > + goto out_remove_vqs; > + } Hm, that failure handling is rather nasty. In virtballoon_freeze() we document: "The workqueue is already frozen by the PM core before this function is called" Your report states: "Workqueue: events page_reporting_process" I assume that workqueue is not frozen yet because ... it's not freezable :) So could we queue to system_freezable_wq instead, or define our own freezable workqueue there? Then a driver doesn't have to worry about that. -- Cheers, David