[PATCH 5.11 096/254] drm/etnaviv: Use FOLL_FORCE for userptr

[Greg Kroah-Hartman]

From: Daniel Vetter <daniel.vetter at ffwll.ch>

commit cd5297b0855f17c8b4e3ef1d20c6a3656209c7b3 upstream.

Nothing checks userptr.ro except this call to pup_fast, which means
there's nothing actually preventing userspace from writing to this.
Which means you can just read-only mmap any file you want, userptr it
and then write to it with the gpu. Not good.

The right way to handle this is FOLL_WRITE | FOLL_FORCE, which will
break any COW mappings and update tracking for MAY_WRITE mappings so
there's no exploit and the vm isn't confused about what's going on.
For any legit use case there's no difference from what userspace can
observe and do.

Reviewed-by: Lucas Stach <l.stach at pengutronix.de>
Cc: stable at vger.kernel.org
Cc: John Hubbard <jhubbard at nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Cc: Lucas Stach <l.stach at pengutronix.de>
Cc: Russell King <linux+etnaviv at armlinux.org.uk>
Cc: Christian Gmeiner <christian.gmeiner at gmail.com>
Cc: etnaviv at lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20210301095254.1946084-1-daniel.vetter@ffwll.ch
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 drivers/gpu/drm/etnaviv/etnaviv_gem.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
@@ -689,7 +689,7 @@ static int etnaviv_gem_userptr_get_pages
 		struct page **pages = pvec + pinned;
 
 		ret = pin_user_pages_fast(ptr, num_pages,
-					  !userptr->ro ? FOLL_WRITE : 0, pages);
+					  FOLL_WRITE | FOLL_FORCE, pages);
 		if (ret < 0) {
 			unpin_user_pages(pvec, pinned);
 			kvfree(pvec);