[PATCH 6.18 376/396] drm/xe/guc: Fix buffer overflow in steered register list allocation

6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tejas Upadhyay <[email protected]>

[ Upstream commit 632ecc90e1ca5d3b6822bb4d08f84a175b6c42c0 ]

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 <[email protected]>
Cc: [email protected]
Assisted-by: GitHub-Copilot:claude-opus-4.6
Reviewed-by: Zhanjun Dong <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Tejas Upadhyay <[email protected]>
(cherry picked from commit 0a78a44f4901aa6c9263e66be7fce02282f1109f)
Signed-off-by: Matthew Brost <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/gpu/drm/xe/xe_guc_capture.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/xe/xe_guc_capture.c
+++ b/drivers/gpu/drm/xe/xe_guc_capture.c
@@ -437,8 +437,15 @@ static void guc_capture_alloc_steered_li
 	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;
+
+		bitmap_or(all_dss, gt->fuse_topo.g_dss_mask, gt->fuse_topo.c_dss_mask,
+			  XE_MAX_DSS_FUSE_BITS);
+
+		total = bitmap_weight(all_dss, XE_MAX_DSS_FUSE_BITS) *
+			guc_capture_get_steer_reg_num(guc_to_xe(guc));
+	}
 
 	if (!total)
 		return;