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([2a01:e0a:f0e:9070:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49ce5927b68sm199544355e9.1.2026.09.04.06.52.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Sep 2026 06:52:45 -0700 (PDT) Message-ID: Date: Fri, 4 Sep 2026 15:52:44 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: eric.auger@redhat.com Subject: Re: [PATCH v3] vfio/platform: prevent read-only region mappings from becoming writable Content-Language: en-US To: Abdifatah Suruur , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Mostafa Saleh , Pranjal Shrivastava , Alex Williamson References: <20260903092907.419-1-suruurism@gmail.com> From: Eric Auger In-Reply-To: <20260903092907.419-1-suruurism@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, On 9/3/26 11:29 AM, 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 Reviewed-by: Eric Auger Thanks Eric > --- > 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); > + > vma->vm_private_data = vdev; > > if (vdev->regions[index].type & VFIO_PLATFORM_REGION_TYPE_MMIO) > return vfio_platform_mmap_mmio(vdev->regions[index], vma); >