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Fri, 4 Sep 2026 22:35:34 +0000 (GMT) From: Anthony Krowiak To: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: jjherne@linux.ibm.com, borntraeger@de.ibm.com, mjrosato@linux.ibm.com, pasic@linux.ibm.com, alex@shazbot.org, kwankhede@nvidia.com, fiuczy@linux.ibm.com, pbonzini@redhat.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com, agordeev@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, stable@vger.kernel.org Subject: [PATCH v7 2/6] s390/vfio-ap: Fix failure to release IRQ notification eventfd contexts Date: Fri, 4 Sep 2026 18:35:27 -0400 Message-ID: <20260904223531.1611088-3-akrowiak@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260904223531.1611088-1-akrowiak@linux.ibm.com> References: <20260904223531.1611088-1-akrowiak@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=bc1bluPB c=1 sm=1 tr=0 ts=6a9b47b9 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=fxeDLeT5AZ2qCvnLJ4gA:9 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTA0MDIwOSBTYWx0ZWRfXwIlEtL4pDisu Dk7K8FPKufoRHadQLX7fQY6vIsJFB7dkoNsRXtkqXZWDJlMHQWp0CN+qKaXf7TkbbE50TBJd6UO ZGRWok+r7t0426DNIJOf57RRyU9ba8E= X-Proofpoint-ORIG-GUID: hRacaFsVQ5O319hKisxxYOixpx2Pwfue X-Proofpoint-GUID: hRacaFsVQ5O319hKisxxYOixpx2Pwfue X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTA0MDIwOSBTYWx0ZWRfX8zdv8M1SiUPz RgKoDXyTQ3be25/ul5CTskE/yjEbjJZVst8jTlRkCO2oLlThYJamhaVjhtPHsaSAIqFJ1SIHedN 9OnKimh3GuEr+faQxxzdYotSvpXq4daHJZ7SqPKgZBWLkFSqoZEHyE1cvpVb9da92h49IJQfq2e acGyLLTDuGus5DCP37DHslpX1vb4VAAe0q3Yi61No+xefIBvh6T91R6PZTdsKtOq15uaAywAHwo DkYnvqFHeTPHysmxjqL1AF110svmpePZlz5e04I8D8zZDqo0gci7MSUhBlVLXNkIKWcEXgHFmDw BSaD2iTYikYb2jIO4FS8vW1CWiFpz+ZwtvwVQ4QjQfNcH1IheraQlqUntxU4XgRjk171LiePsfh 9XtW4uP0Dl2BRv5bM/ySyUldoADU9IT4Vnn+aRLTbDb7pIfZeFrGq9dHkC5Yua5u+y5w3C3OL41 lA6VrExtduZGtX22YAA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-04_06,2026-09-03_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 suspectscore=0 adultscore=0 malwarescore=0 spamscore=0 lowpriorityscore=0 phishscore=0 clxscore=1015 priorityscore=1501 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609040209 When userspace registers IRQ notification eventfds via the VFIO_DEVICE_SET_IRQS ioctl, vfio_ap_set_request_irq() and vfio_ap_set_cfg_change_irq() each call eventfd_ctx_fdget(), which takes a reference on the eventfd_ctx and stores it in matrix_mdev->req_trigger and matrix_mdev->cfg_chg_trigger respectively. These references are dropped only when userspace explicitly replaces or clears them via a subsequent SET_IRQS call. If the device is closed without that explicit teardown - because the guest exits, the VM process crashes, or the device file is simply closed - neither vfio_ap_mdev_close_device() nor the remove path releases these references. The eventfd_ctx backing objects and their associated file references therefore leak for the lifetime of the kernel. Fix this by introducing vfio_ap_mdev_release_eventfds() and calling it from vfio_ap_mdev_close_device() after vfio_ap_mdev_unset_kvm(). The VFIO core guarantees that close_device is called before vfio_unregister_group_dev() returns in the remove path, so fixing close_device is sufficient to cover both teardown paths. Note: ~~~~ The matrix_dev->mdevs lock must be held during the call to vfio_ap_mdev_release_eventfds(). There is a small window between the calls to vfio_ap_mdev_unset_kvm() which gets and releases the update locks and the acquisition of the matrix_dev->mdevs_lock mutex during which it is possible - although highly unlikely during normal operation - whereby a concurrent SET_IRQS call can get in. Taking matrix_dev->mdevs_lock around vfio_ap_mdev_release_eventfds() is sufficient to make this race-free. The SET_IRQS ioctl path writes req_trigger and cfg_chg_trigger only from vfio_ap_mdev_ioctl(), which holds mdevs_lock for its entire duration and always calls eventfd_ctx_put() on the previous value before storing the new one. Any number of concurrent SET_IRQS calls during the window between vfio_ap_mdev_unset_kvm() and the acquisition of mdevs_lock are therefore safe: each ioctl invocation puts the reference it found and installs a new one, leaving exactly one live reference in the field when it releases the lock. When release_eventfds subsequently acquires mdevs_lock it finds that single surviving reference and puts it. Conversely, a SET_IRQS call that loses the race and blocks on mdevs_lock will find the field NULL after release_eventfds finishes, take ownership of the reference it just created, and install it into a field that will never be read again - a transient leak. To close that final case, callers must ensure no new SET_IRQS ioctls can be issued after close_device() is called, which the VFIO core guarantees by releasing the device file before invoking close_device(). Fixes: bf48961f6f48e ("s390/vfio-ap: realize the VFIO_DEVICE_SET_IRQS ioctl") Cc: stable@vger.kernel.org Signed-off-by: Anthony Krowiak Reviewed-by: Matthew Rosato --- drivers/s390/crypto/vfio_ap_ops.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index 9d4f5b9e3301..4a31454d725a 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -2209,12 +2209,28 @@ static int vfio_ap_mdev_open_device(struct vfio_device *vdev) return vfio_ap_mdev_set_kvm(matrix_mdev, vdev->kvm); } +static void vfio_ap_mdev_release_eventfds(struct ap_matrix_mdev *matrix_mdev) +{ + if (matrix_mdev->req_trigger) { + eventfd_ctx_put(matrix_mdev->req_trigger); + matrix_mdev->req_trigger = NULL; + } + if (matrix_mdev->cfg_chg_trigger) { + eventfd_ctx_put(matrix_mdev->cfg_chg_trigger); + matrix_mdev->cfg_chg_trigger = NULL; + } +} + static void vfio_ap_mdev_close_device(struct vfio_device *vdev) { struct ap_matrix_mdev *matrix_mdev = container_of(vdev, struct ap_matrix_mdev, vdev); vfio_ap_mdev_unset_kvm(matrix_mdev); + + mutex_lock(&matrix_dev->mdevs_lock); + vfio_ap_mdev_release_eventfds(matrix_mdev); + mutex_unlock(&matrix_dev->mdevs_lock); } static void vfio_ap_mdev_request(struct vfio_device *vdev, unsigned int count) -- 2.53.0