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[35.189.192.250]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49cee60d9c6sm56979455e9.11.2026.09.03.02.07.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Sep 2026 02:07:47 -0700 (PDT) Date: Thu, 3 Sep 2026 09:07:43 +0000 From: Mostafa Saleh To: Abdifatah Suruur Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Eric Auger , Pranjal Shrivastava , Alex Williamson Subject: Re: [PATCH v2] vfio/platform: prevent read-only region mappings from becoming writable Message-ID: References: <20260903071955.13144-1-suruurism@gmail.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260903071955.13144-1-suruurism@gmail.com> On Thu, Sep 03, 2026 at 10:19:55AM +0300, Abdifatah Suruur wrote: > vfio_platform_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 ptp: vmclock (commit > a5edadbae57e2298a56cf7a4e774a027905a331f). nit: checkpatch(--strict) fails with: Please use git commit description style 'commit <12+ chars of sha1> ("")' - ie: 'commit a5edadbae57e ("ptp: vmclock: prevent read-only mappings from becoming writable")' > > Note this is defensive hardening: no in-tree platform driver currently > publishes a region without the WRITE flag. The guard costs nothing and > keeps the mmap() interface honest if a read-only region ever appears. > > Fixes: de49fc0d99e6a ("vfio/platform: initial skeleton of VFIO support for platform devices") This only adds a stub for vfio_platform_mmap(), The right one is Fixes: fad4d5b1f042 ("vfio/platform: support MMAP of MMIO regions") > Signed-off-by: Abdifatah Suruur <suruurism@gmail.com> Reviewed-by: Mostafa Saleh <smostafa@google.com> Thanks, Mostafa > --- > v2: commit log now states plainly that the read-only path is > unreachable in practice, per Alex's review; dropped Cc: stable as > there is no reachable issue to backport. > > --- a/drivers/vfio/platform/vfio_platform_common.c > +++ b/drivers/vfio/platform/vfio_platform_common.c > @@ -594,7 +594,11 @@ > 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 = vdev; > > if (vdev->regions[index].type & VFIO_PLATFORM_REGION_TYPE_MMIO) > return vfio_platform_mmap_mmio(vdev->regions[index], vma);