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 57E3752B1DE; Wed, 30 Sep 2026 17:40:45 +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=1790790046; cv=none; b=JljPqphHOdxHZk8gv/r3Gj587hkI8DryqXYWbu1xYTLHjmdlb+ZjSYeWqjQ9SwHcTIJVgzM7VqwPPB4W+ZDkZGXY2mac1DNMZjz6IOJ7r499rIkkxbfT3gLzqmhuehIKDr/2xk49nMNxkvFaBNXjfiergfg+hUfS1Q/bHbCm4R0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790790046; c=relaxed/simple; bh=gCBq5ZfZiNBjsGECyjWYPA5/W9OZ8Bxt0yqsVrEoSOg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GkXefuVgKL6LVRT4zeuh1l8x/Ki6nozdW9q0LtYYfutu5xsFgyVYpest4TesnL0M5lesiDwVOFq0cwCBT5NgmeBaHHAqrjKy1hMKwPIgKoLyciNlEUng5MyFbcwFPoCdkxuEaEywSTmjNibYKgGANhGHUDRYvy2ZSTuk8wPZ3G0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=KaPqIb2B; 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="KaPqIb2B" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C6431F000FF; Wed, 30 Sep 2026 17:40:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790790045; bh=lSSIbT/+48HRGU5P/zRsbehWUTtGGj4UEPUMEd1MTCQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=KaPqIb2BXwB2azmUV683O+FcaPQMq+h5PFmXhLP0ES2iZs0zJp9bxu4plNrlb6hs5 dBQbMoKGJimJfrnsEvDjItpIyr2hoyGIzKge9m92XHxHEZZchtF3pYWi1GgqIYOZPd UP+iGQjnXDTyVwluzJysewWUmezcFCkNBwyskAW4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Anthony Krowiak , Matthew Rosato , Christian Borntraeger , Sasha Levin Subject: [PATCH 6.12 646/877] s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects Date: Wed, 30 Sep 2026 17:25:57 +0200 Message-ID: <20260930152428.599389600@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152414.738996857@linuxfoundation.org> References: <20260930152414.738996857@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Anthony Krowiak [ Upstream commit 7fa61c29850d05e40ca9ed41bfdf57673023f581 ] 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 [ Omitted deletion of cfg_chg_trigger initialization because the field is absent in Linux 6.12. ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/s390/crypto/vfio_ap_ops.c | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -786,11 +786,17 @@ static int vfio_ap_mdev_probe(struct mde ret = vfio_register_emulated_iommu_dev(&matrix_mdev->vdev); if (ret) goto err_put_vdev; - matrix_mdev->req_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: @@ -2247,6 +2253,8 @@ static struct ap_matrix_mdev *vfio_ap_md 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)) @@ -2266,6 +2274,7 @@ static ssize_t status_show(struct device 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); @@ -2314,6 +2323,7 @@ static ssize_t status_show(struct device done: mutex_unlock(&matrix_dev->mdevs_lock); + mutex_unlock(&matrix_dev->guests_lock); return nchars; } @@ -2746,6 +2756,12 @@ static void vfio_ap_mdev_cfg_add(unsigne 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) { /* * The mdevs_lock must be held in order to access fields @@ -2813,6 +2829,10 @@ void vfio_ap_on_cfg_changed(struct ap_co 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);