CVE-2026-68276: drm/amdgpu/gfx: fix cleaner shader IB buffer overflow

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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

drm/amdgpu/gfx: fix cleaner shader IB buffer overflow

The cleaner shader sysfs path allocates a 16-dword (64 byte) IB but
incorrectly fills (align_mask + 1) dwords. On GFX rings align_mask is
0xff, so the loop wrote 256 dwords into a 64-byte buffer, causing a
kernel page fault.

The IB only needs to be a minimal NOP shell to schedule the job; the
cleaner shader itself is emitted on the ring via emit_cleaner_shader().
Fill 16 dwords to match the allocation.

v2: Use ib_size_dw variable (Lijo)

(cherry picked from commit bf21af331ebf72d0935fd70c73192414a422c03a)

The Linux kernel CVE team has assigned CVE-2026-68276 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.12 with commit d361ad5d2fc0e4d59d5d538092c9b37889756642 and fixed in 6.12.103 with commit 201633f47b542a99bb7baafdfcda7781249fb3d9
	Issue introduced in 6.12 with commit d361ad5d2fc0e4d59d5d538092c9b37889756642 and fixed in 6.18.42 with commit e28420e36542ae8b66a5bdcec419525f521bddf8
	Issue introduced in 6.12 with commit d361ad5d2fc0e4d59d5d538092c9b37889756642 and fixed in 7.1.6 with commit 9cd9a983769a4d0e9cc80a287316ee79685d38b3
	Issue introduced in 6.12 with commit d361ad5d2fc0e4d59d5d538092c9b37889756642 and fixed in 7.2-rc1 with commit 3e864bf2a32a1cbdf1e0f9c5a5a4176e8575f4a3

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-68276
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/201633f47b542a99bb7baafdfcda7781249fb3d9
	https://git.kernel.org/stable/c/e28420e36542ae8b66a5bdcec419525f521bddf8
	https://git.kernel.org/stable/c/9cd9a983769a4d0e9cc80a287316ee79685d38b3
	https://git.kernel.org/stable/c/3e864bf2a32a1cbdf1e0f9c5a5a4176e8575f4a3