drm/vmwgfx: use check_add_overflow for shader size+offset bound

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>
Reviewed-by: Ian Forbes <ian.forbes@broadcom.com>
Link: https://patch.msgid.link/20260505222728.519626-12-zack.rusin@broadcom.com

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c b/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c
index eca4e3e97eb4ec9411b734aa96ad25ea3b217fa0..39811cf19db154891c87b71435a498a74d0e7151 100644 (file)
--- 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 @@ out:
 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 @@ out_err:
 
 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;