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 7B5B618787A for ; Fri, 11 Sep 2026 00:39:28 +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=1789087169; cv=none; b=Gryz2wilsffTPrmM3PP/qQICPwZ9GeqsguDMTZG8YSHHs3gnBn7ppcpubvmFFyrfyan7iIdC5/G3z7uCZ94gWQE0gXSI75KlpkezRDiw1SlmP9VTyE2Qag19l/g1TEuf4L/kqk/ZRa1m40oP2Vcp4DYsC5fhdEHmr/v5v4UWj8U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789087169; c=relaxed/simple; bh=ziKJg4MrqzCNgKx6U62Gj/zP197cAGaTSEeBBXsescY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=raHFVvhuRR4owo83VPqaebAv31c4qo+uincxiR5AmGO7hLyXvrMfNFk9q5EeGBihXaDgk+Dfe+0Uyxl/34yhOqvZbi/vvi3/XvJRCTM9KiSdN7DpensOv41fIDI104CJYwO6+D/H2n8ME9SluAN1R6cgbSZmWFCTDq2HwaPAZbg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QLw12iBs; 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="QLw12iBs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6EBE61F000FF; Fri, 11 Sep 2026 00:39:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789087168; bh=/xUIeiDxCU97BV7CkA4x5RD7oYkFR3RXhzMWIMzolQQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=QLw12iBs1U0wtdURNgXsoFRWmuoCn6Mb+xcLRGEPMnVxkDbrA/+Td1B4qMUBzBFZZ o6exWgsBa6yKWVrmQfj2Ae9Foy7gtDL8C7etu2sKmeCNamFvDVLI6wWbW3SNHM9uhT 67iKzNWZIs7s7YY6mXjwHGY3TBvWUxe8TEVUAMyeOos+y8vJ1yCImdac6wz/CDfFP9 C7t/M4m1n1rYy4r4f+vOBvyne4LDWqjUhrCeLAChr5W3fBjST3cJ4/K6pyr+t1nYiD yY3MTSOS+rtIoLbFEKVD8a4lnrZUAZSYFAwOLyNb2Ic2Z6iQaGKws+luSJaGmmcY8T AcHj4wCFCNGLg== From: Sasha Levin To: stable@vger.kernel.org Cc: Anthony Krowiak , Matthew Rosato , Christian Borntraeger , Sasha Levin Subject: [PATCH 6.6.y] s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects Date: Thu, 10 Sep 2026 20:39:25 -0400 Message-ID: <20260911003925.3551684-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026090918-pout-capsule-bd86@gregkh> References: <2026090918-pout-capsule-bd86@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 --- drivers/s390/crypto/vfio_ap_ops.c | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index d4151f519e8b2..e54cb1be641bb 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -763,11 +763,17 @@ 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; + + /* + * 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: @@ -2049,6 +2055,8 @@ 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)) @@ -2068,6 +2076,7 @@ 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); @@ -2098,6 +2107,7 @@ static ssize_t status_show(struct device *dev, } mutex_unlock(&matrix_dev->mdevs_lock); + mutex_unlock(&matrix_dev->guests_lock); return nchars; } @@ -2503,6 +2513,12 @@ 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); @@ -2562,6 +2578,10 @@ 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); -- 2.53.0