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

Overview

In the Linux kernel, the following vulnerability has been resolved:

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)

(cherry picked from commit 0a78a44f4901aa6c9263e66be7fce02282f1109f)

Affected

• Linux >= b170d696c1e2226713471d810c63b1162335079f < b485bfb45555163bfa5f565d6a3415fcb3035b02
• Linux >= b170d696c1e2226713471d810c63b1162335079f < a9a020f3c11eba6573b699f9cf9245a51b025ade
• Linux >= b170d696c1e2226713471d810c63b1162335079f < 632ecc90e1ca5d3b6822bb4d08f84a175b6c42c0
• Linux 6.13

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.