drm/panthor: Flush shmem writes before mapping buffers CPU-uncached

[ Upstream commit 576c930e5e7dcb937648490611a83f1bf0171048 ]

The shmem layer zeroes out the new pages using cached mappings, and if
we don't CPU-flush we might leave dirty cachelines behind, leading to
potential data leaks and/or asynchronous buffer corruption when dirty
cachelines are evicted.

Fixes: 8a1cc07578bf ("drm/panthor: Add GEM logical block")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patch.msgid.link/20251107171214.1186299-1-boris.brezillon@collabora.com
[Harshit: Resolve conflicts due to missing commit: fe69a3918084
("drm/panthor: Fix UAF in panthor_gem_create_with_handle() debugfs
code") in 6.12.y]
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
index 0438b80a6434b421e83172c598dd3516daa93e97..09b318fb8e7cdb6225793ad423a58e2497c02870 100644 (file)
--- a/drivers/gpu/drm/panthor/panthor_gem.c
+++ b/drivers/gpu/drm/panthor/panthor_gem.c
@@ -214,6 +214,23 @@ panthor_gem_create_with_handle(struct drm_file *file,
                bo->base.base.resv = bo->exclusive_vm_root_gem->resv;
        }
 
+       /* If this is a write-combine mapping, we query the sgt to force a CPU
+        * cache flush (dma_map_sgtable() is called when the sgt is created).
+        * This ensures the zero-ing is visible to any uncached mapping created
+        * by vmap/mmap.
+        * FIXME: Ideally this should be done when pages are allocated, not at
+        * BO creation time.
+        */
+       if (shmem->map_wc) {
+               struct sg_table *sgt;
+
+               sgt = drm_gem_shmem_get_pages_sgt(shmem);
+               if (IS_ERR(sgt)) {
+                       ret = PTR_ERR(sgt);
+                       goto out_put_gem;
+               }
+       }
+
        /*
         * Allocate an id of idr table where the obj is registered
         * and handle has the id what user can see.
@@ -222,6 +239,7 @@ panthor_gem_create_with_handle(struct drm_file *file,
        if (!ret)
                *size = bo->base.base.size;
 
+out_put_gem:
        /* drop reference from allocate - handle holds it now. */
        drm_gem_object_put(&shmem->base);