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Mon, 21 Sep 2026 05:23:43 -0700 (PDT) Received: from SurHub.localdomain ([196.188.112.50]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6aa67b5eddcsm4228761a12.0.2026.09.21.05.23.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Sep 2026 05:23:42 -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 2/7] vfio/fsl-mc: prevent read-only region mappings from becoming writable Date: Mon, 21 Sep 2026 15:23:29 +0300 Message-ID: <20260921122334.2099-3-suruurism@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260921122334.2099-1-suruurism@gmail.com> References: <20260921122334.2099-1-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 --- --- a/drivers/vfio/fsl-mc/vfio_fsl_mc.c +++ b/drivers/vfio/fsl-mc/vfio_fsl_mc.c @@ -406,7 +406,11 @@ 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)) + vm_flags_clear(vma, VM_MAYWRITE); + vma->vm_private_data = mc_dev; return vfio_fsl_mc_mmap_mmio(vdev->regions[index], vma); }