CVE-2026-98654: drm/amd/display: Atomize IRQ register read/modify/write ops

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

drm/amd/display: Atomize IRQ register read/modify/write ops

[Why]

The OTG_GLOBAL_SYNC_STATUS register controls various HW IRQ sources for
the output timing generator (OTG). VUPDATE_NO_LOCK is one of them.

To enable the IRQ, driver sets the VUPDATE_NO_LOCK_EN bit in the
GLOBAL_SYNC_STATUS register.

To ack the IRQ after it fires, the driver sets the VUPDATE_NO_LOCK_CLEAR
bit in the same GLOBAL_SYNC_STATUS register.

The bit sets are done through read/modify/write operations, which are
not atomic. Thus, the following race is possible:

    Thread A:                       IRQ handler:
                                    *HW IRQ fires*
    # IRQ disable
    val = read(GLOBAL_SYNC_STATUS)
    unset(val, VUPDATE_NO_LOCK_EN)
    write(val, GLOBAL_SYNC_STATUS)
                                    # ACK reads VUPDATE_NO_LOCK_EN unset
                                    val1 = read(GLOBAL_SYNC_STATUS)
                                    set(val1, VUPDATE_NO_LOCK_CLEAR)
    # IRQ enable
    val = read(GLOBAL_SYNC_STATUS)
    set(val, VUPDATE_NO_LOCK_EN)
    write(val, GLOBAL_SYNC_STATUS)
                                    # BAD! clears VUPDATE_NO_LOCK_EN
                                    write(val1, GLOBAL_SYNC_STATUS)

Regarding the tagged Fixes: change, it appears the change made this race
more likely to occur. Since VUPDATE_NO_LOCK is now the sole IRQ source
for vblank handling, a single race on high refresh panels can lead to a
time out.

[How]

The GLOBAL_SYNC_STATUS register is only one example, other IRQ control
registers also share the same scheme. On top of GLOBAL_SYNC_STATUS,
let's clean up those as well.

To keep things simple, Let's atomize the IRQ rmw ops via a single
driver-wide spinlock. Due to the small scope of this lock, it is
unlikely to cause noticeable overhead on top of all the existing locking
within the IRQ set/handle paths.

Since DM is responsible for locking, wrap dc_interrupt_set/ack with the
spinlock in the new amdgpu_dm_irq_set/ack functions. Migrate/drop all
references in DM to dc_interrupt_set/ack to use amdgpu_dm_irq_set/ack
instead.

(cherry picked from commit 70de0a0216583a53c946155f8c8adedfdca6b4e7)

The Linux kernel CVE team has assigned CVE-2026-98654 to this issue.


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

	Issue introduced in 7.3-rc1 with commit c87e6635d2db02c88ae8d09529362da672d34770 and fixed in 7.3-rc4 with commit 63e19ef3ddab806c472748c825f4dc88dcd994e8

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-2026-98654
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/display/amdgpu_dm/amdgpu_dm.c
	drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
	drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
	drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
	drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_irq.c
	drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_irq.h
	drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_crtc_test.c
	drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_helpers_test.c
	drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_irq_test.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/63e19ef3ddab806c472748c825f4dc88dcd994e8