drm/xe/guc: Fix buffer overflow in steered register list allocation

The size calculation for the steered register extarray uses only the
geometry DSS mask (g_dss_mask) to determine the number of entries to
allocate:

  total = bitmap_weight(gt->fuse_topo.g_dss_mask, ...) * steer_reg_num;

However, the filling loop uses for_each_dss_steering(), which iterates
over for_each_dss(), defined as the union of g_dss_mask and c_dss_mask
(geometry + compute DSS). On platforms with compute-only DSS bits, the
loop writes past the allocated buffer, corrupting adjacent slab objects.

This manifests as list_del corruption and SLUB redzone overwrites during
drm_managed_release on device unbind, since the overflow corrupts the
drmres list_head of neighboring allocations.

Fix by computing the allocation size using the union of both DSS masks,
matching the iteration pattern of for_each_dss_steering().

--
v2:
- use bitmap_weighted_or() (Zhanjun)

Fixes: b170d696c1e2 ("drm/xe/guc: Add XE_LP steered register lists")
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/8049
Cc: Zhanjun Dong <zhanjun.dong@intel.com>
Cc: stable@vger.kernel.org
Assisted-by: GitHub-Copilot:claude-opus-4.6
Reviewed-by: Zhanjun Dong <zhanjun.dong@intel.com>
Link: https://patch.msgid.link/20260612070401.543305-2-tejas.upadhyay@intel.com
Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
(cherry picked from commit 0a78a44f4901aa6c9263e66be7fce02282f1109f)
Signed-off-by: Matthew Brost <matthew.brost@intel.com>

diff --git a/drivers/gpu/drm/xe/xe_guc_capture.c b/drivers/gpu/drm/xe/xe_guc_capture.c
index 21f7caf9ea08499c2d100d4657e0c6668ade04c0..1a019137ddf42bcab8387c130fd474dfbe98beea 100644 (file)
--- a/drivers/gpu/drm/xe/xe_guc_capture.c
+++ b/drivers/gpu/drm/xe/xe_guc_capture.c
@@ -461,8 +461,14 @@ static void guc_capture_alloc_steered_lists(struct xe_guc *guc)
        if (!list || guc->capture->extlists)
                return;
 
-       total = bitmap_weight(gt->fuse_topo.g_dss_mask, sizeof(gt->fuse_topo.g_dss_mask) * 8) *
-               guc_capture_get_steer_reg_num(guc_to_xe(guc));
+       {
+               xe_dss_mask_t all_dss;
+
+               total = bitmap_weighted_or(all_dss, gt->fuse_topo.g_dss_mask,
+                                          gt->fuse_topo.c_dss_mask,
+                                          XE_MAX_DSS_FUSE_BITS) *
+                       guc_capture_get_steer_reg_num(guc_to_xe(guc));
+       }
 
        if (!total)
                return;