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Tue, 29 Sep 2026 02:48:57 -0700 (PDT) Received: from SurHub.localdomain ([196.188.113.7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a00cf9b72fsm89821455e9.9.2026.09.29.02.48.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Sep 2026 02:48:57 -0700 (PDT) From: Abdifatah Suruur To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: alex@shazbot.org, eric.auger@redhat.com, smostafa@google.com, praan@google.com, ioana.ciornei@nxp.com, nipun.gupta@amd.com, nikhil.agarwal@amd.com Subject: [PATCH v2 2/7] vfio/fsl-mc: prevent read-only region mappings from becoming writable Date: Tue, 29 Sep 2026 12:48:43 +0300 Message-ID: <20260929094848.7439-3-suruurism@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260929094848.7439-1-suruurism@gmail.com> References: <20260929094848.7439-1-suruurism@gmail.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit vfio_fsl_mc_mmap() rejects writable mappings of regions without the WRITE flag, but leaves VM_MAYWRITE set. Userspace can map such a region read-only and then upgrade the mapping to writable with mprotect(). Clear VM_MAYWRITE for regions without the WRITE flag, as i915 does for its read-only objects and as fixed in drm/vc4 (CVE-2026-68445), drm/panthor (CVE-2024-53071) and commit a5edadbae57e ("ptp: vmclock: prevent read-only mappings from becoming writable"). Note this is defensive hardening: the fsl-mc bus publishes all device regions with the WRITE flag set, so no device can currently reach the read-only path. The guard costs nothing and keeps the mmap() interface honest if a read-only region ever appears. Fixes: 67247289688d4 ("vfio/fsl-mc: Allow userspace to MMAP fsl-mc device MMIO regions") Signed-off-by: Abdifatah Suruur Reviewed-by: Ioana Ciornei --- drivers/vfio/fsl-mc/vfio_fsl_mc.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/drivers/vfio/fsl-mc/vfio_fsl_mc.c b/drivers/vfio/fsl-mc/vfio_fsl_mc.c index b4c3958201b25..5a6cd78dcc06a 100644 --- a/drivers/vfio/fsl-mc/vfio_fsl_mc.c +++ b/drivers/vfio/fsl-mc/vfio_fsl_mc.c @@ -403,9 +403,13 @@ static int vfio_fsl_mc_mmap(struct vfio_device *core_vdev, && (vma->vm_flags & VM_READ)) return -EINVAL; - if (!(vdev->regions[index].flags & VFIO_REGION_INFO_FLAG_WRITE) - && (vma->vm_flags & VM_WRITE)) - return -EINVAL; + /* Prevent read-only region mappings from being upgraded with mprotect() */ + if (!(vdev->regions[index].flags & VFIO_REGION_INFO_FLAG_WRITE)) { + if (vma->vm_flags & VM_WRITE) + return -EINVAL; + + vm_flags_clear(vma, VM_MAYWRITE); + } vma->vm_private_data = mc_dev; -- 2.53.0