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vfio/platform: prevent read-only region mappings from becoming writable

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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 a5edadbae5 ("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: fad4d5b1f0 ("vfio/platform: support MMAP of MMIO regions")
Reviewed-by: Mostafa Saleh <smostafa@google.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Pranjal Shrivastava <praan@google.com>
Signed-off-by: Abdifatah Suruur <suruurism@gmail.com>
Link: https://lore.kernel.org/r/20260929094848.7439-2-suruurism@gmail.com
Signed-off-by: Alex Williamson <alex@shazbot.org>
This commit is contained in:
Abdifatah Suruur 2026-09-29 12:48:42 +03:00 committed by Alex Williamson
parent a1c1731c24
commit 420bed9131
1 changed files with 7 additions and 3 deletions
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10
drivers/vfio/platform/vfio_platform_common.c
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@ -591,9 +591,13 @@ int vfio_platform_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma
&& (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 = vdev;