Re: [PATCH] xen/gntdev: prevent private mappings from becoming writable

[Juergen Gross]

On 19.08.26 10:42, Abdifatah Suruur wrote:
> gntdev_mmap() rejects writable private (non-shared) mappings of foreign
> grant pages, because a private writable mapping takes the COW path on
> pages that have no proper struct-page backing.  However, VM_MAYWRITE is
> left set, so userspace can map the grant read-only and then upgrade the
> mapping to writable with mprotect(), hitting the same COW path the
> check was written to prevent.
>
> Clear VM_MAYWRITE for private mappings, as i915 does for its read-only
> objects and as fixed in drm/vc4 (CVE-2026-68445) and drm/panthor
> (CVE-2024-53071) and ptp: vmclock (commit
> a5edadbae57e2298a56cf7a4e774a027905a331f).
>
> Fixes: ab31523c2fcac ("xen/gntdev: allow usermode to map granted pages")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Abdifatah Suruur <suruurism@xxxxxxxxx>

Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

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