Re: [PATCH v3] vfio/fsl-mc: prevent read-only region mappings from becoming writable

[Ioana Ciornei]

On Thu, Sep 03, 2026 at 12:29:12PM +0300, Abdifatah Suruur wrote:
> 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 <suruurism@xxxxxxxxx>

Reviewed-by: Ioana Ciornei <ioana.ciornei@xxxxxxx>

Thanks!