[PATCH 11/12] drm/vmwgfx: use check_add_overflow for shader size+offset bound

[Zack Rusin <zack.rusin@broadcom.com>]

vmw_shader_define() validates the user-supplied shader window against
its backing buffer with

	(u64)buffer->tbo.base.size < (u64)size + (u64)offset

drm_vmw_shader_create_arg::offset is __u64 in the uapi; when it is
near U64_MAX the unsigned addition wraps and the resulting tiny value
passes the check.  The unbounded offset is then stored in
res->guest_memory_offset and forwarded to host SVGA shader-create
commands.

Use check_add_overflow() to detect the wrap and compare the resulting
endpoint against the buffer size.

Fixes: 668b206601c5 ("drm/vmwgfx: Stop using raw ttm_buffer_object's")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4.7
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_shader.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c b/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c
index eca4e3e97eb4..39811cf19db1 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c
@@ -25,6 +25,8 @@
  *
  **************************************************************************/
 
+#include <linux/overflow.h>
+
 #include <drm/ttm/ttm_placement.h>
 
 #include "vmwgfx_binding.h"
@@ -685,7 +687,7 @@ int vmw_shader_destroy_ioctl(struct drm_device *dev, void *data,
 static int vmw_user_shader_alloc(struct vmw_private *dev_priv,
 				 struct vmw_bo *buffer,
 				 size_t shader_size,
-				 size_t offset,
+				 u64 offset,
 				 SVGA3dShaderType shader_type,
 				 uint8_t num_input_sig,
 				 uint8_t num_output_sig,
@@ -739,7 +741,7 @@ static int vmw_user_shader_alloc(struct vmw_private *dev_priv,
 static struct vmw_resource *vmw_shader_alloc(struct vmw_private *dev_priv,
 					     struct vmw_bo *buffer,
 					     size_t shader_size,
-					     size_t offset,
+					     u64 offset,
 					     SVGA3dShaderType shader_type)
 {
 	struct vmw_shader *shader;
@@ -768,7 +770,7 @@ static struct vmw_resource *vmw_shader_alloc(struct vmw_private *dev_priv,
 
 static int vmw_shader_define(struct drm_device *dev, struct drm_file *file_priv,
 			     enum drm_vmw_shader_type shader_type_drm,
-			     u32 buffer_handle, size_t size, size_t offset,
+			     u32 buffer_handle, size_t size, u64 offset,
 			     uint8_t num_input_sig, uint8_t num_output_sig,
 			     uint32_t *shader_handle)
 {
@@ -779,13 +781,16 @@ static int vmw_shader_define(struct drm_device *dev, struct drm_file *file_priv,
 	int ret;
 
 	if (buffer_handle != SVGA3D_INVALID_ID) {
+		u64 end;
+
 		ret = vmw_user_bo_lookup(file_priv, buffer_handle, &buffer);
 		if (unlikely(ret != 0)) {
 			VMW_DEBUG_USER("Couldn't find buffer for shader creation.\n");
 			return ret;
 		}
 
-		if ((u64)buffer->tbo.base.size < (u64)size + (u64)offset) {
+		if (check_add_overflow((u64)size, (u64)offset, &end) ||
+		    end > buffer->tbo.base.size) {
 			VMW_DEBUG_USER("Illegal buffer- or shader size.\n");
 			ret = -EINVAL;
 			goto out_bad_arg;
-- 
2.51.0