CVE-2022-49565

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

perf/x86/intel/lbr: Fix unchecked MSR access error on HSW

The fuzzer triggers the below trace.

[ 7763.384369] unchecked MSR access error: WRMSR to 0x689 (tried to write 0x1fffffff8101349e) at rIP: 0xffffffff810704a4 (native_write_msr+0x4/0x20) [ 7763.397420] Call Trace: [ 7763.399881] <TASK> [ 7763.401994] intel_pmu_lbr_restore+0x9a/0x1f0 [ 7763.406363] intel_pmu_lbr_sched_task+0x91/0x1c0 [ 7763.410992] __perf_event_task_sched_in+0x1cd/0x240

On a machine with the LBR format LBR_FORMAT_EIP_FLAGS2, when the TSX is disabled, a TSX quirk is required to access LBR from registers. The lbr_from_signext_quirk_needed() is introduced to determine whether the TSX quirk should be applied. However, the lbr_from_signext_quirk_needed() is invoked before the intel_pmu_lbr_init(), which parses the LBR format information. Without the correct LBR format information, the TSX quirk never be applied.

Move the lbr_from_signext_quirk_needed() into the intel_pmu_lbr_init(). Checking x86_pmu.lbr_has_tsx in the lbr_from_signext_quirk_needed() is not required anymore.

Both LBR_FORMAT_EIP_FLAGS2 and LBR_FORMAT_INFO have LBR_TSX flag, but only the LBR_FORMAT_EIP_FLAGS2 requirs the quirk. Update the comments accordingly.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.