CVE-2024-26937

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

drm/i915/gt: Reset queue_priority_hint on parking

Originally, with strict in order execution, we could complete execution only when the queue was empty. Preempt-to-busy allows replacement of an active request that may complete before the preemption is processed by HW. If that happens, the request is retired from the queue, but the queue_priority_hint remains set, preventing direct submission until after the next CS interrupt is processed.

This preempt-to-busy race can be triggered by the heartbeat, which will also act as the power-management barrier and upon completion allow us to idle the HW. We may process the completion of the heartbeat, and begin parking the engine before the CS event that restores the queue_priority_hint, causing us to fail the assertion that it is MIN.

<3>[ 166.210729] __engine_park:283 GEM_BUG_ON(engine->sched_engine->queue_priority_hint != (-((int)(~0U » 1)) - 1)) <0>[ 166.210781] Dumping ftrace buffer: <0>[ 166.210795] ——————————— … <0>[ 167.302811] drm_fdin-1097 2..s1. 165741070us : trace_ports: 0000:00:02.0 rcs0: promote { ccid:20 1217:2 prio 0 } <0>[ 167.302861] drm_fdin-1097 2d.s2. 165741072us : execlists_submission_tasklet: 0000:00:02.0 rcs0: preempting last=1217:2, prio=0, hint=2147483646 <0>[ 167.302928] drm_fdin-1097 2d.s2. 165741072us : __i915_request_unsubmit: 0000:00:02.0 rcs0: fence 1217:2, current 0 <0>[ 167.302992] drm_fdin-1097 2d.s2. 165741073us : __i915_request_submit: 0000:00:02.0 rcs0: fence 3:4660, current 4659 <0>[ 167.303044] drm_fdin-1097 2d.s1. 165741076us : execlists_submission_tasklet: 0000:00:02.0 rcs0: context:3 schedule-in, ccid:40 <0>[ 167.303095] drm_fdin-1097 2d.s1. 165741077us : trace_ports: 0000:00:02.0 rcs0: submit { ccid:40 3:4660* prio 2147483646 } <0>[ 167.303159] kworker/-89 11….. 165741139us : i915_request_retire.part.0: 0000:00:02.0 rcs0: fence c90:2, current 2 <0>[ 167.303208] kworker/-89 11….. 165741148us : __intel_context_do_unpin: 0000:00:02.0 rcs0: context:c90 unpin <0>[ 167.303272] kworker/-89 11….. 165741159us : i915_request_retire.part.0: 0000:00:02.0 rcs0: fence 1217:2, current 2 <0>[ 167.303321] kworker/-89 11….. 165741166us : __intel_context_do_unpin: 0000:00:02.0 rcs0: context:1217 unpin <0>[ 167.303384] kworker/-89 11….. 165741170us : i915_request_retire.part.0: 0000:00:02.0 rcs0: fence 3:4660, current 4660 <0>[ 167.303434] kworker/-89 11d..1. 165741172us : __intel_context_retire: 0000:00:02.0 rcs0: context:1216 retire runtime: { total:56028ns, avg:56028ns } <0>[ 167.303484] kworker/-89 11….. 165741198us : __engine_park: 0000:00:02.0 rcs0: parked <0>[ 167.303534] -0 5d.H3. 165741207us : execlists_irq_handler: 0000:00:02.0 rcs0: semaphore yield: 00000040 <0>[ 167.303583] kworker/-89 11….. 165741397us : __intel_context_retire: 0000:00:02.0 rcs0: context:1217 retire runtime: { total:325575ns, avg:0ns } <0>[ 167.303756] kworker/-89 11….. 165741777us : __intel_context_retire: 0000:00:02.0 rcs0: context:c90 retire runtime: { total:0ns, avg:0ns } <0>[ 167.303806] kworker/-89 11….. 165742017us : __engine_park: __engine_park:283 GEM_BUG_ON(engine->sched_engine->queue_priority_hint != (-((int)(~0U » 1)) - 1)) <0>[ 167.303811] ——————————— <4>[ 167.304722] ————[ cut here ]———— <2>[ 167.304725] kernel BUG at drivers/gpu/drm/i915/gt/intel_engine_pm.c:283! <4>[ 167.304731] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI <4>[ 167.304734] CPU: 11 PID: 89 Comm: kworker/11:1 Tainted: G W 6.8.0-rc2-CI_DRM_14193-gc655e0fd2804+ #1 <4>[ 167.304736] Hardware name: Intel Corporation Rocket Lake Client Platform/RocketLake S UDIMM 6L RVP, BIOS RKLSFWI1.R00.3173.A03.2204210138 04/21/2022 <4>[ 167.304738] Workqueue: i915-unordered retire_work_handler [i915] <4>[ 16 —truncated—

Weakness

The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

Affected Software

Extended Description

While assertion is good for catching logic errors and reducing the chances of reaching more serious vulnerability conditions, it can still lead to a denial of service. For example, if a server handles multiple simultaneous connections, and an assert() occurs in one single connection that causes all other connections to be dropped, this is a reachable assertion that leads to a denial of service.

Potential Mitigations

References

• https://git.kernel.org/stable/c/3b031e4fcb2740988143c303f81f69f18ce86325
• https://git.kernel.org/stable/c/4a3859ea5240365d21f6053ee219bb240d520895
• https://git.kernel.org/stable/c/67944e6db656bf1e986aa2a359f866f851091f8a
• https://git.kernel.org/stable/c/7eab7b021835ae422c38b968d5cc60e99408fb62
• https://git.kernel.org/stable/c/8fd9b0ce8c26533fe4d5d15ea15bbf7b904b611c
• https://git.kernel.org/stable/c/ac9b6b3e8d1237136c8ebf0fa1ce037dd7e2948f
• https://git.kernel.org/stable/c/aed034866a08bb7e6e34d50a5629a4d23fe83703
• https://git.kernel.org/stable/c/fe34587acc995e7b1d7a5d3444a0736721ec32b3
• https://git.kernel.org/stable/c/3b031e4fcb2740988143c303f81f69f18ce86325
• https://git.kernel.org/stable/c/4a3859ea5240365d21f6053ee219bb240d520895
• https://git.kernel.org/stable/c/67944e6db656bf1e986aa2a359f866f851091f8a
• https://git.kernel.org/stable/c/7eab7b021835ae422c38b968d5cc60e99408fb62
• https://git.kernel.org/stable/c/8fd9b0ce8c26533fe4d5d15ea15bbf7b904b611c
• https://git.kernel.org/stable/c/ac9b6b3e8d1237136c8ebf0fa1ce037dd7e2948f
• https://git.kernel.org/stable/c/aed034866a08bb7e6e34d50a5629a4d23fe83703
• https://git.kernel.org/stable/c/fe34587acc995e7b1d7a5d3444a0736721ec32b3
• https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html