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

drm/xe: harden adjust_idledly() against divide-by-zero and overflow

adjust_idledly() has several corner-case issues flagged during review:

1. If xe_gt_clock_init() failed to recognise the crystal clock,
gt->info.timestamp_base is 0, which makes idledly_units_ps also 0.
The subsequent DIV_ROUND_CLOSEST(..., idledly_units_ps) is then a
divide-by-zero and panics the kernel.

2. The tick-to-ns conversions are done in u32:
idledly * idledly_units_ps, (maxcnt - 1) * 1000
Both overflow u32 before DIV_ROUND_CLOSEST() sees them.

3. If IDLE_WAIT_TIME reads back as 0, maxcnt evaluates to 0 and
the maxcnt - 1 clamp wraps to 0xFFFFFFFF in u32.

4. The register only stores whole ticks, so the clamped ns value has
to be converted to ticks and back. DIV_ROUND_CLOSEST() can round
that conversion up past maxcnt:

maxcnt = 640 ns, one tick = 666664 ps

clamp: maxcnt - 1 = 639 ns
ns -> ticks: 639000 / 666664 = 0.958 -> rounds to 1 tick
tick -> ns: 1 * 666664 / 1000 = 667 ns

667 ns is programmed into RING_IDLEDLY, but 667 >= maxcnt (640),
so xe_gt_WARN_ON() fires again on every subsequent init.

Return early if timestamp_base is 0 (the unknown-crystal path).
Do the conversions in u64 via the *_ULL() helpers so they cannot wrap.
Clamp with a floor (DIV_ROUND_DOWN_ULL) so the programmed delay stays
strictly below maxcnt, and guard the maxcnt == 0 case with a zero delay
while still writing RING_IDLEDLY so INHIBIT_SWITCH_UNTIL_PREEMPTED is
cleared.

v2: Drop the redundant warn on the timestamp_base == 0 path;
xe_gt_clock_init() already warns on an unrecognised crystal clock.
Keep the early return to avoid the divide-by-zero. - Vinay

v3: Field-mask the RING_IDLEDLY write with REG_FIELD_PREP(IDLE_DELAY, ...)
instead of writing the raw tick count, which could clobber
INHIBIT_SWITCH_UNTIL_PREEMPTED and reserved bits. Split the
inhibit-switch clear from the maxcnt clamp so a set inhibit bit no
longer forces a needless delay overwrite when the delay itself is
already valid. Use gt_to_xe(gt) instead of gt_to_xe(hwe->gt).

(cherry picked from commit d864065ea25e9d12897c175de9176ce46677e176)
Published: 2026-10-23
Score: n/a
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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History

Fri, 23 Oct 2026 16:15:00 +0000

Type Values Removed Values Added
First Time appeared Linux linux
Vendors & Products Linux linux

Fri, 23 Oct 2026 12:30:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: drm/xe: harden adjust_idledly() against divide-by-zero and overflow adjust_idledly() has several corner-case issues flagged during review: 1. If xe_gt_clock_init() failed to recognise the crystal clock, gt->info.timestamp_base is 0, which makes idledly_units_ps also 0. The subsequent DIV_ROUND_CLOSEST(..., idledly_units_ps) is then a divide-by-zero and panics the kernel. 2. The tick-to-ns conversions are done in u32: idledly * idledly_units_ps, (maxcnt - 1) * 1000 Both overflow u32 before DIV_ROUND_CLOSEST() sees them. 3. If IDLE_WAIT_TIME reads back as 0, maxcnt evaluates to 0 and the maxcnt - 1 clamp wraps to 0xFFFFFFFF in u32. 4. The register only stores whole ticks, so the clamped ns value has to be converted to ticks and back. DIV_ROUND_CLOSEST() can round that conversion up past maxcnt: maxcnt = 640 ns, one tick = 666664 ps clamp: maxcnt - 1 = 639 ns ns -> ticks: 639000 / 666664 = 0.958 -> rounds to 1 tick tick -> ns: 1 * 666664 / 1000 = 667 ns 667 ns is programmed into RING_IDLEDLY, but 667 >= maxcnt (640), so xe_gt_WARN_ON() fires again on every subsequent init. Return early if timestamp_base is 0 (the unknown-crystal path). Do the conversions in u64 via the *_ULL() helpers so they cannot wrap. Clamp with a floor (DIV_ROUND_DOWN_ULL) so the programmed delay stays strictly below maxcnt, and guard the maxcnt == 0 case with a zero delay while still writing RING_IDLEDLY so INHIBIT_SWITCH_UNTIL_PREEMPTED is cleared. v2: Drop the redundant warn on the timestamp_base == 0 path; xe_gt_clock_init() already warns on an unrecognised crystal clock. Keep the early return to avoid the divide-by-zero. - Vinay v3: Field-mask the RING_IDLEDLY write with REG_FIELD_PREP(IDLE_DELAY, ...) instead of writing the raw tick count, which could clobber INHIBIT_SWITCH_UNTIL_PREEMPTED and reserved bits. Split the inhibit-switch clear from the maxcnt clamp so a set inhibit bit no longer forces a needless delay overwrite when the delay itself is already valid. Use gt_to_xe(gt) instead of gt_to_xe(hwe->gt). (cherry picked from commit d864065ea25e9d12897c175de9176ce46677e176)
Title drm/xe: harden adjust_idledly() against divide-by-zero and overflow
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

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Linux Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-10-23T12:05:08.723Z

Reserved: 2026-09-25T10:25:14.380Z

Link: CVE-2026-98919

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-23T13:17:12.487

Modified: 2026-10-23T13:17:12.487

Link: CVE-2026-98919

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-23T16:00:15Z

Weaknesses

No weakness.