CVE-2024-26721: drm/i915/dsc: Fix the macro that calculates DSCC_/DSCA_ PPS reg address

CVE-2024-26721: drm/i915/dsc: Fix the macro that calculates DSCC_/DSCA_ PPS reg address

[Greg Kroah-Hartman]

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

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

drm/i915/dsc: Fix the macro that calculates DSCC_/DSCA_ PPS reg address

Commit bd077259d0a9 ("drm/i915/vdsc: Add function to read any PPS
register") defines a new macro to calculate the DSC PPS register
addresses with PPS number as an input. This macro correctly calculates
the addresses till PPS 11 since the addresses increment by 4. So in that
case the following macro works correctly to give correct register
address:

_MMIO(_DSCA_PPS_0 + (pps) * 4)

However after PPS 11, the register address for PPS 12 increments by 12
because of RC Buffer memory allocation in between. Because of this
discontinuity in the address space, the macro calculates wrong addresses
for PPS 12 - 16 resulting into incorrect DSC PPS parameter value
read/writes causing DSC corruption.

This fixes it by correcting this macro to add the offset of 12 for PPS
>=12.

v3: Add correct paranthesis for pps argument (Jani Nikula)

(cherry picked from commit 6074be620c31dc2ae11af96a1a5ea95580976fb5)

The Linux kernel CVE team has assigned CVE-2024-26721 to this issue.


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

	Issue introduced in 6.7 with commit bd077259d0a9 and fixed in 6.7.6 with commit ff5999fb03f4
	Issue introduced in 6.7 with commit bd077259d0a9 and fixed in 6.8 with commit 962ac2dce56b

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-2024-26721
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/i915/display/intel_vdsc_regs.h


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/ff5999fb03f467e1e7159f0ddb199c787f7512b9
	https://git.kernel.org/stable/c/962ac2dce56bb3aad1f82a4bbe3ada57a020287c