From: Daniel Vetter <daniel.vetter@xxxxxxxx> 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@xxxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Cc: John Hubbard <jhubbard@xxxxxxxxxx> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx> Cc: Russell King <linux+etnaviv@xxxxxxxxxxxxxxx> Cc: Christian Gmeiner <christian.gmeiner@xxxxxxxxx> Cc: etnaviv@xxxxxxxxxxxxxxxxxxxxx Link: https://patchwork.freedesktop.org/patch/msgid/20210301095254.1946084-1-daniel.vetter@xxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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);
