Description

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

perf/x86/intel: Fix segfault with PEBS-via-PT with sample_freq

Currently, using PEBS-via-PT with a sample frequency instead of a sample
period, causes a segfault. For example:

BUG: kernel NULL pointer dereference, address: 0000000000000195

? __die_body.cold+0x19/0x27
? page_fault_oops+0xca/0x290
? exc_page_fault+0x7e/0x1b0
? asm_exc_page_fault+0x26/0x30
? intel_pmu_pebs_event_update_no_drain+0x40/0x60
? intel_pmu_pebs_event_update_no_drain+0x32/0x60
intel_pmu_drain_pebs_icl+0x333/0x350
handle_pmi_common+0x272/0x3c0
intel_pmu_handle_irq+0x10a/0x2e0
perf_event_nmi_handler+0x2a/0x50

That happens because intel_pmu_pebs_event_update_no_drain() assumes all the
pebs_enabled bits represent counter indexes, which is not always the case.
In this particular case, bits 60 and 61 are set for PEBS-via-PT purposes.

The behaviour of PEBS-via-PT with sample frequency is questionable because
although a PMI is generated (PEBS_PMI_AFTER_EACH_RECORD), the period is not
adjusted anyway.

Putting that aside, fix intel_pmu_pebs_event_update_no_drain() by passing
the mask of counter bits instead of 'size'. Note, prior to the Fixes
commit, 'size' would be limited to the maximum counter index, so the issue
was not hit.

Classification

CVE ID: CVE-2025-38055

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.02% (probability of being exploited)

EPSS Percentile: 2.45% (scored less or equal to compared to others)

EPSS Date: 2025-06-20 (when was this score calculated)

References

https://nvd.nist.gov/vuln/detail/CVE-2025-38055
https://git.kernel.org/stable/c/ca51db23166767a8445deb8331c9b8d5205d9287
https://git.kernel.org/stable/c/0b1874a5b1173fbcb2185ab828f4c33d067e551e
https://git.kernel.org/stable/c/99bcd91fabada0dbb1d5f0de44532d8008db93c6

Timeline