drm/etnaviv: Use FOLL_FORCE for userptr
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@pengutronix.de> Cc: stable@vger.kernel.org Cc: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Cc: Lucas Stach <l.stach@pengutronix.de> Cc: Russell King <linux+etnaviv@armlinux.org.uk> Cc: Christian Gmeiner <christian.gmeiner@gmail.com> Cc: etnaviv@lists.freedesktop.org Link: https://patchwork.freedesktop.org/patch/msgid/20210301095254.1946084-1-daniel.vetter@ffwll.ch
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