CVE-2026-93275

Summary

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

perf/x86/intel/pt: Fix stop/start with no update

If pt_event_stop() is called without PERF_EF_UPDATE flag, then perf_aux_output_end() is not called. A subsequent call to pt_event_start() will call perf_aux_output_begin() again which violates the rule against nesting and triggers a WARNING in perf_aux_output_begin().

Originally, pt_event_stop() was never called without PERF_EF_UPDATE, because the only code paths to do so are from event overflow, and Intel PT does not do that.

However the introduction of group throttling by commit 9734e25fbf5ae ("perf: Fix the throttle logic for a group") meant that an Intel PT event could be throttled if it was part of a group. Throttling calls PMU ->stop() / ->start() callbacks without flags.

An example is when AUX area sampling is used. The following commands hit the issue:

echo 10000 > /proc/sys/kernel/perf_event_max_sample_rate

perf record -F32000 –aux-sample -e '{intel_pt//u,cycles:u}'
– bash -c 'for i in seq 1 100000 ; do true ; done'

Use PERF_HES_UPTODATE to track whether perf_aux_output_begin() and perf_aux_output_end() are balanced. A cleared PERF_HES_UPTODATE bit indicates that an AUX output context is still open.

Amend pt_event_start() / pt_event_stop() accordingly so that begin/end stay balanced:

• In non-snapshot mode, stop() always closes the buffer (the buffer may have run out of space, and that accounting is done by the update), so a following start() opens a fresh one as before.

• In snapshot/overwrite mode, stop() without PERF_EF_UPDATE leaves the buffer open so that pt_event_snapshot_aux() can still copy from it, and start() then only re-enables tracing instead of calling perf_aux_output_begin() again.

Note that pt_event_del() calls pt_event_stop() with PERF_EF_UPDATE flag set (as is required by the documentation), so a final call to perf_aux_output_end() is assured.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/9b919fb5512f256e9e0604faf960b2bb98aab454
• https://git.kernel.org/stable/c/cab5015ee3f25f789b4a368f2abfa65536576b78
• https://git.kernel.org/stable/c/304844b5545f444d523286da8228a1cbc46ffffa
• https://git.kernel.org/stable/c/2e17bf3a469a41457a3bc31b1f8fd66b6ce94a6d

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