perf/core: Fix NULL pmu_ctx passed to pmu->sched_task()

Overview

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

perf/core: Fix NULL pmu_ctx passed to pmu->sched_task()

perf_pmu_sched_task() returns early when cpuctx->task_ctx is set, and cpc->task_epc is only non-NULL while a task context is scheduled in on this CPU. __perf_pmu_sched_task() therefore always passes NULL:

Unable to handle kernel NULL pointer dereference at virtual address 00 pc : armv8pmu_sched_task+0x14/0x50 Call trace: armv8pmu_sched_task+0x14/0x50 (P) perf_pmu_sched_task+0xac/0x108 __perf_event_task_sched_out+0x6c/0xe0

Pass &cpc->epc instead, the CPU-wide context for this PMU, which the function already dereferences a few lines up to find pmu.

armv8pmu_sched_task() is the only in-tree implementation that dereferences the argument, and it only reads ->pmu, so the oops needs BRBE, added in v6.17.

Affected

• Linux >= bd27568117664b8b3e259721393df420ed51f57b < b5409311b606d536cc485f3706c242c2afa93edb
• Linux >= bd27568117664b8b3e259721393df420ed51f57b < 249a2bd87a0e57dc28f36e992807edc9cae309b5
• Linux >= bd27568117664b8b3e259721393df420ed51f57b < ec15f6a50183fc01f470af74ad49900fb3731fca
• Linux >= bd27568117664b8b3e259721393df420ed51f57b < 36bb85cf36cab15fb611cb44b78a5df06e4e69a2
• Linux 6.2

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.