[PATCH v2] drm/i915: Prevent writing into a read-only object via a GGTT mmap

[Chris Wilson]

Quoting Bloomfield, Jon (2018-06-14 17:36:29)
> > -----Original Message-----
> > From: Chris Wilson <chris at chris-wilson.co.uk>
> > Sent: Thursday, June 14, 2018 9:07 AM
> > To: intel-gfx at lists.freedesktop.org
> > Cc: dri-devel at lists.freedesktop.org; Chris Wilson <chris at chris-wilson.co.uk>;
> > Bloomfield, Jon <jon.bloomfield at intel.com>; Joonas Lahtinen
> > <joonas.lahtinen at linux.intel.com>; Matthew Auld
> > <matthew.william.auld at gmail.com>; David Herrmann
> > <dh.herrmann at gmail.com>
> > Subject: [PATCH v2] drm/i915: Prevent writing into a read-only object via a
> > GGTT mmap
> > 
> > If the user has created a read-only object, they should not be allowed
> > to circumvent the write protection by using a GGTT mmapping. Deny it.
> > 
> > Also most machines do not support read-only GGTT PTEs, so again we have
> > to reject attempted writes. Fortunately, this is known a priori, so we
> > can at least reject in the call to create the mmap (with a sanity check
> > in the fault handler).
> > 
> > v2: Check the vma->vm_flags during mmap() to allow readonly access.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Jon Bloomfield <jon.bloomfield at intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > Cc: Matthew Auld <matthew.william.auld at gmail.com>
> > Cc: David Herrmann <dh.herrmann at gmail.com>
> 
> Shame about the BUG_ON, but probably overkill to add code to suppress
> the RO flag just for mmap.
> 
> Reviewed-by: Jon Bloomfield <jon.bloomfield at intel.com>

Maybe one day with a PIN_RO, we can put it back in again.
Just a feeling of unease for shadowing cache_level on the vma. If only
we could just erase the history of doing cache_domain tracking.
-Chris