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.
v3: Remove VM_MAYWRITE to curtail mprotect()

Testcase: igt/gem_userptr_blits/readonly_mmap*
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Cc: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Matthew Auld <matthew.william.auld@gmail.com> #v1
Reviewed-by: Jon Bloomfield <jon.bloomfield@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180712185315.3288-4-chris@chris-wilson.co.uk

1 files changed, 1 insertions, 0 deletions

diff --git a/include/drm/drm_vma_manager.h b/include/drm/drm_vma_manager.h
index 8758df94e9a0..c7987daeaed0 100644
--- a/include/drm/drm_vma_manager.h
+++ b/include/drm/drm_vma_manager.h
@@ -41,6 +41,7 @@ struct drm_vma_offset_node {
 	rwlock_t vm_lock;
 	struct drm_mm_node vm_node;
 	struct rb_root vm_files;
+	bool readonly:1;
 };
 
 struct drm_vma_offset_manager {