CVE-2026-90047

What the bug is

get_flat_ccs_offset() reads the base of the flat CCS storage from the hardware, scales it by the number of enabled L3 nodes, and rounds the result up to 128K. Everything below that offset is then handed to the VRAM allocator as usable memory. Rounding a limit that means "usable memory ends here" upwards publishes whatever lies between the real base and the rounded one as free memory, and that memory belongs to the compression hardware. The scaled value has no reason to be 128K aligned, and on a Battlemage G21 with 16 GiB it is not: flat CCS base: raw 0x3fafff800, rounded 0x3fb000000 so the last 2 KiB of page 0x3fafff000 is CCS storage, in the allocator's pool. Whatever is allocated there gets that tail overwritten by the compression hardware, which needs no page-table entry, no buffer object and no GPU submission to do it, and does it before userspace exists. On this machine a Mesa VM's level-3 page table landed on that page on every cold boot. It lost the entry covering the compositor's batch-buffer heap, so the compositor's first submission faulted fetching its batch and gdm restarted it forever: a black screen on an otherwise working machine. Restarting gdm cleared it because the next VM's page tables were allocated somewhere else. Round down instead, to the page size the allocator works in. On this machine that excludes exactly one page. Reading the reserved page afterwards shows what had been writing it: [369] 0xcccc000000000000 [371] 0xcc77000000000000 [373] 0xcccc000000000000 [375] 0xcc77000000000000 compression metadata, two bytes per sixteen, sitting where the driver used to hand out memory. The assertion that should have caught this compares the offset against GSMBASE - ccs_size for equality. That value is 128K aligned, so it agrees with the rounded-up offset precisely when the base is not aligned - the check cannot fail in the case it exists to catch, and is compiled out unless CONFIG_DRM_XE_DEBUG is set. Replace it with one that can fail: CCS storage must not run into GSM. [ And this was a debug session from hell, enormously helped by an AI doing much of the grunt-work. I'd like to call it my tireless helper, but the AI several times stated flat out that this was impossible and unsolvable and that we should just write a report about it. I suspect those things have been trained by people who may not be quite as stubborn as I am. But while the AI was ready to give up several times, it did keep adding debug code and analyzing it faithfully when I pushed. So credit where credit is due and I let the AI write the commit message above. This is basically a one-liner fixing a bogus "round_up()" to a "round_down()", but there were 24 patches adding more and more debug information to this, and 18 kernel boot to finally narrow it down to this. - Linus ]

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

drivers/gpu/drm/xe/xe_vram.c

What this is

INTEL DRM XE DRIVER (Lunar Lake and newer)MAINTAINERS section matched on drivers/gpu/drm/xe/ · intel-xe@lists.freedesktop.org · Supported

Kernel module

xe

Check it on the machine

grep -w CONFIG_DRM_XE /boot/config-$(uname -r)

Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.

lsmod | grep -w xe

Prints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.

Show whether Debian builds this, per release

Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed. The build rule could not be established for 1 release, so nothing is claimed about those.

• bookworm?
• trixieMnot built on amd64/cloud-amd64, arm64/arm64-16k, arm64/cloud-arm64, armel/rpi, ppc64el/powerpc64le-64k, s390x/s390x
• forky, sidMnot built on amd64/cloud-amd64, arm64/arm64-16k, arm64/cloud-arm64, loong64/loong64, ppc64el/powerpc64le-64k, s390x/s390x

?

not established - no Makefile entry for the affected file

M

a module where it is built at all; some flavours do not build it

Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.

Build switch

CONFIG_DRM_XE

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages

Signals

Published

2026-09-16 (33 days ago)source

CVSS

7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it

Attack vector

local (AV:L)source

EPSS

0.17%, higher than 6.3% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

unimportantsource

Subsystem

drivers/gpu

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
6.13	6.18.51	c96477e0cabf
6.13	7.2.5	348c3db4f152
6.13	7.3	818bebeb63dd