[PATCH 2/2] drm/amdgpu: Dirty cleared blocks on allocation

[Natalie Vock]

If we hand out cleared blocks to users, they are expected to write
at least some non-zero values somewhere. If we keep the CLEAR bit set on
the block, amdgpu_fill_buffer will assume there is nothing to do and
incorrectly skip clearing the block. Ultimately, the (still dirty) block
will be reused as if it were cleared, without any wiping of the memory
contents.

Most severely, this means that any buffer allocated with
AMDGPU_GEM_CREATE_VRAM_CLEARED | AMDGPU_GEM_CREATE_WIPE_ON_RELEASE
(which is the case for **all userspace buffers**) are neither
guaranteed to contain cleared VRAM, nor are they being wiped on
release, potentially leaking application memory to arbitrary other
applications.

Fixes: a68c7eaa7a8ff ("drm/amdgpu: Enable clear page functionality")
Cc: stable at vger.kernel.org

Link: https://gitlab.freedesktop.org/drm/amd/-/issues/3812

Signed-off-by: Natalie Vock <natalie.vock at gmx.de>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
index 2d7f82e98df9..cecc67d0f0b8 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
@@ -591,6 +591,13 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
 	list_for_each_entry(block, &vres->blocks, link) {
 		unsigned long start;
 
+		/*
+		 * Allocated blocks may be dirtied as soon as we return.
+		 * Mark all blocks as dirty here, otherwise we might
+		 * incorrectly assume the memory is still zeroed.
+		 */
+		drm_buddy_block_set_dirty(block);
+
 		start = amdgpu_vram_mgr_block_start(block) +
 			amdgpu_vram_mgr_block_size(block);
 		start >>= PAGE_SHIFT;
-- 
2.49.0