CVE-2026-68445: drm/vc4: Prevent shader BO mappings from becoming writable

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

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

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

drm/vc4: Prevent shader BO mappings from becoming writable

vc4_gem_object_mmap() rejects a writable mapping of a validated shader
BO, but leaves VM_MAYWRITE set.  Userspace can map the BO read-only and
then turn it writable with mprotect().

Validated shader BOs must stay read-only: the validator checks the
instructions once and the GPU trusts them afterwards.  A writable
mapping lets userspace rewrite the code after validation, bypassing the
validator.

Clear VM_MAYWRITE on the read-only path so the mapping cannot be
upgraded, as i915 already does for its read-only objects.

The Linux kernel CVE team has assigned CVE-2026-68445 to this issue.


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

	Issue introduced in 4.5 with commit 463873d5701427f2964a0b4b72c45f1f14b6df87 and fixed in 6.6.148 with commit 9f0ee411fc2d76333d6087c5862ffa907cf7a175
	Issue introduced in 4.5 with commit 463873d5701427f2964a0b4b72c45f1f14b6df87 and fixed in 6.12.101 with commit 019e6ad247f7fd038d2e009789f6d9bfcccb1ae7
	Issue introduced in 4.5 with commit 463873d5701427f2964a0b4b72c45f1f14b6df87 and fixed in 6.18.42 with commit 6deaa317201851c644c431b57682e54d06b35838
	Issue introduced in 4.5 with commit 463873d5701427f2964a0b4b72c45f1f14b6df87 and fixed in 7.1.6 with commit fe168ef1d232d734d9998fd74822e2e20930dfff
	Issue introduced in 4.5 with commit 463873d5701427f2964a0b4b72c45f1f14b6df87 and fixed in 7.2-rc5 with commit 0c9e6367639548307d3f578f6943ce72c9d39087

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-2026-68445
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/vc4/vc4_bo.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/9f0ee411fc2d76333d6087c5862ffa907cf7a175
	https://git.kernel.org/stable/c/019e6ad247f7fd038d2e009789f6d9bfcccb1ae7
	https://git.kernel.org/stable/c/6deaa317201851c644c431b57682e54d06b35838
	https://git.kernel.org/stable/c/fe168ef1d232d734d9998fd74822e2e20930dfff
	https://git.kernel.org/stable/c/0c9e6367639548307d3f578f6943ce72c9d39087