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 A46FE215161 for ; Wed, 9 Sep 2026 09:58:37 +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=1788947919; cv=none; b=rbum4q0lOltu4e8jq1iy0lHpr8qI9joQob9vKAFDeMhfUrk4Z1HlqbYfJC4LulZAigSPIiqsWxi2UhscMnZcHpaRJsaHIvafC/k3B8406GkR/iTwDk2RqhqqF6uaAjMMYG7o8ciPzO7N62Ze7yRU2UffqRfVIESz91uVUT1ecjY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788947919; c=relaxed/simple; bh=3xpB+s+oGCli/17t/deTboYeck2oxOe73rd4vEEIR74=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=qa6gpw6giAiCv2W0xWtq1qOWOfDwZ2CMcGEPZp42xWLB+cJIyyQY8GC0WL5pR07Y1xTq2Cf+6izmBo4XTJ2fmj5RRGVPCj2rsvgdWeEfru7ONhntPjKBP08FZknJQ+a0f3C8fm9RKlCFd46n5hqbLpdhx2jgwRHeWTsHaYoGCPM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=idZmkzTv; 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="idZmkzTv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E1AE1F00A3D; Wed, 9 Sep 2026 09:58:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788947917; bh=7RBQBpDG+8Fcn4oNB5GJ2P1FQzwfhGXDXcIQOO/UWGY=; h=Subject:To:Cc:From:Date; b=idZmkzTvlFWsdwkCMbnhrhxfb6NLJbVaAoEbfhfd4kKb7QuA/y91KEhhlCzDFxL3k 0g7rVG18wikcgC4LSvEjtv9YksuMhYUn3GYuoefPZ9txDJjS4+omm1pbdVKNVUyQDv cXnZtN9caHS5rDEhKNECBcnTtbC71cB6SbjfAEus= Subject: FAILED: patch "[PATCH] s390/vfio-ap: Fix missing lock required to access list of" failed to apply to 6.12-stable tree To: akrowiak@linux.ibm.com,borntraeger@linux.ibm.com,mjrosato@linux.ibm.com Cc: From: Date: Wed, 09 Sep 2026 11:54:17 +0200 Message-ID: <2026090917-landmass-partridge-4557@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.12-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x 7fa61c29850d05e40ca9ed41bfdf57673023f581 # git commit -s git send-email --to '' --in-reply-to '2026090917-landmass-partridge-4557@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 7fa61c29850d05e40ca9ed41bfdf57673023f581 Mon Sep 17 00:00:00 2001 From: Anthony Krowiak Date: Wed, 12 Aug 2026 16:02:34 -0400 Subject: [PATCH] s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects In order to traverse or add/remove ap_matrix_mdev objects in the matrix_dev->mdev_list, the matrix_dev->guests_lock mutex must be held. There are two functions that access the list without holding the mutex: vfio_ap_mdev_probe function ~~~~~~~~~~~~~~~~~~~~~~~~~~~ The vfio_ap_mdev_probe function uses the matrix_dev->mdevs_lock mutex to guard the add of a newly created ap_matrix_mdev object to the matrix_dev->mdev_list. This mutex does not protect list access; its purpose is to guard against concurrent access to fields contained in an ap_matrix_mdev object. This could lead to kernel memory corruption or use-after-free if another mdev is created or removed concurrently. The adding of an ap_matrix_mdev object to matrix_dev->mdev_list is now guarded by the matrix_dev->guests_lock which is the correct way to protect against concurrent mdev_list access. Also removed the following two lines of code because the matrix_mdev is allocated via vfio_alloc_device macro which uses kzalloc, so req_trigger and cfg_chg_trigger are already zero-initialised when the struct is allocated before the call to vfio_register_emulated_iommu_dev. This prevents a window whereby these triggers are set to NULL after the device is exposed to userspace. matrix_mdev->req_trigger = NULL; matrix_mdev->cfg_chg_trigger = NULL; vfio_ap_mdev_for_queue function ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The status_show function that supports display of the status attribute of the devices in /sys/bus/ap/devices calls the vfio_ap_mdev_for_queue function which iterates the matrix_dev->mdev_list to find the object representing the queue device whose status is to be displayed. In order to traverse this list, the matrix_dev->guests_lock mutex must be held. To fix this, the guests_lock mutex is taken prior to taking the matrix_dev->mdevs_lock mutex in the status_show function. It is taken there rather than the vfio_ap_mdev_for_queue function - where it is needed - because it must be taken prior to the mdevs_lock mutex in order to adhere to the proper locking order and prevent a lockdep splat; also because the mdevs_lock is needed there to access fields within the matrix_mdev object in that function. See the vfio-ap-locking.rst in the linux kernel tree. Fixes: 2c1ee8983aa3 ("s390/vfio-ap: prepare for dynamic update of guest's APCB on queue probe/remove") Cc: stable@vger.kernel.org Signed-off-by: Anthony Krowiak Reviewed-by: Matthew Rosato Signed-off-by: Christian Borntraeger diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index 1076a9982923..a403d0f59122 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -807,12 +807,17 @@ static int vfio_ap_mdev_probe(struct mdev_device *mdev) ret = vfio_register_emulated_iommu_dev(&matrix_mdev->vdev); if (ret) goto err_put_vdev; - matrix_mdev->req_trigger = NULL; - matrix_mdev->cfg_chg_trigger = NULL; + + /* + * Take the matrix_dev->guests_lock mutex before adding the matrix_mdev + * to the mdev_list. All functions that traverse the list must also hold + * this lock to guard against additions to or removals from the list + * while it is being traversed. + */ + mutex_lock(&matrix_dev->guests_lock); dev_set_drvdata(&mdev->dev, matrix_mdev); - mutex_lock(&matrix_dev->mdevs_lock); list_add(&matrix_mdev->node, &matrix_dev->mdev_list); - mutex_unlock(&matrix_dev->mdevs_lock); + mutex_unlock(&matrix_dev->guests_lock); return 0; err_put_vdev: @@ -2292,6 +2297,8 @@ static struct ap_matrix_mdev *vfio_ap_mdev_for_queue(struct vfio_ap_queue *q) unsigned long apid = AP_QID_CARD(q->apqn); unsigned long apqi = AP_QID_QUEUE(q->apqn); + lockdep_assert_held(&matrix_dev->guests_lock); + list_for_each_entry(matrix_mdev, &matrix_dev->mdev_list, node) { if (test_bit_inv(apid, matrix_mdev->matrix.apm) && test_bit_inv(apqi, matrix_mdev->matrix.aqm)) @@ -2311,6 +2318,7 @@ static ssize_t status_show(struct device *dev, struct ap_matrix_mdev *matrix_mdev; struct ap_device *apdev = to_ap_dev(dev); + mutex_lock(&matrix_dev->guests_lock); mutex_lock(&matrix_dev->mdevs_lock); q = dev_get_drvdata(&apdev->device); matrix_mdev = vfio_ap_mdev_for_queue(q); @@ -2338,6 +2346,7 @@ static ssize_t status_show(struct device *dev, } mutex_unlock(&matrix_dev->mdevs_lock); + mutex_unlock(&matrix_dev->guests_lock); return nchars; } @@ -2756,6 +2765,12 @@ static void vfio_ap_mdev_cfg_add(unsigned long *apm_add, unsigned long *aqm_add, vfio_ap_filter_apid_by_qtype(apm_add, aqm_add); + /* + * It is safe to traverse this list here because the + * required guard - matrix_dev->guests_lock - is taken in the + * vfio_ap_on_cfg_changed function prior to this function getting + * called. + */ list_for_each_entry(matrix_mdev, &matrix_dev->mdev_list, node) { bitmap_and(matrix_mdev->apm_add, matrix_mdev->matrix.apm, apm_add, AP_DEVICES); @@ -2815,6 +2830,10 @@ void vfio_ap_on_cfg_changed(struct ap_config_info *cur_cfg_info, if (!cur_cfg_info || !prev_cfg_info) return; + /* + * Take the guests_lock mutex here to guard access to the + * matrix_dev->mdev_list in the two functions called below. + */ mutex_lock(&matrix_dev->guests_lock); vfio_ap_mdev_on_cfg_remove(cur_cfg_info, prev_cfg_info);