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[34.142.210.164]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39b25f8d2c5sm5029514a91.2.2026.09.04.07.17.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Sep 2026 07:17:20 -0700 (PDT) Date: Fri, 4 Sep 2026 14:17:15 +0000 From: Pranjal Shrivastava To: Abdifatah Suruur Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Eric Auger , Mostafa Saleh , Alex Williamson Subject: Re: [PATCH v3] vfio/platform: prevent read-only region mappings from becoming writable Message-ID: References: <20260903092907.419-1-suruurism@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260903092907.419-1-suruurism@gmail.com> On Thu, Sep 03, 2026 at 12:29:07PM +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 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: fad4d5b1f042 ("vfio/platform: support MMAP of MMIO regions") > Signed-off-by: Abdifatah Suruur > Reviewed-by: Mostafa Saleh > --- > 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. > v3: use 'commit ("")' style for the vmclock reference > and point Fixes at the MMAP support commit, per Mostafa's review. > > --- 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); > + Minor Nit: We seem to be evaluating this condition twice, back-to-back: if (!(vdev->regions[index].flags & VFIO_REGION_INFO_FLAG_WRITE)) We could consolidate this into a single block to make the intent and flow cleaner: /* Prevent read-only region mappings from [...] */ if (!(vdev->regions[index].flags & VFIO_REGION_INFO_FLAG_WRITE)) { if (vma->vm_flags & VM_WRITE) return -EINVAL; vm_flags_clear(vma, VM_MAYWRITE); } Apart from that, Reviewed-by: Pranjal Shrivastava <praan@google.com> Thanks, Praan