CVE-2026-23435 (GCVE-0-2026-23435)

Vulnerability from cvelistv5 – Published: 2026-04-03 15:15 – Updated: 2026-05-23 16:04
VLAI?
Title
perf/x86: Move event pointer setup earlier in x86_pmu_enable()
Summary
In the Linux kernel, the following vulnerability has been resolved: perf/x86: Move event pointer setup earlier in x86_pmu_enable() A production AMD EPYC system crashed with a NULL pointer dereference in the PMU NMI handler: BUG: kernel NULL pointer dereference, address: 0000000000000198 RIP: x86_perf_event_update+0xc/0xa0 Call Trace: <NMI> amd_pmu_v2_handle_irq+0x1a6/0x390 perf_event_nmi_handler+0x24/0x40 The faulting instruction is `cmpq $0x0, 0x198(%rdi)` with RDI=0, corresponding to the `if (unlikely(!hwc->event_base))` check in x86_perf_event_update() where hwc = &event->hw and event is NULL. drgn inspection of the vmcore on CPU 106 showed a mismatch between cpuc->active_mask and cpuc->events[]: active_mask: 0x1e (bits 1, 2, 3, 4) events[1]: 0xff1100136cbd4f38 (valid) events[2]: 0x0 (NULL, but active_mask bit 2 set) events[3]: 0xff1100076fd2cf38 (valid) events[4]: 0xff1100079e990a90 (valid) The event that should occupy events[2] was found in event_list[2] with hw.idx=2 and hw.state=0x0, confirming x86_pmu_start() had run (which clears hw.state and sets active_mask) but events[2] was never populated. Another event (event_list[0]) had hw.state=0x7 (STOPPED|UPTODATE|ARCH), showing it was stopped when the PMU rescheduled events, confirming the throttle-then-reschedule sequence occurred. The root cause is commit 7e772a93eb61 ("perf/x86: Fix NULL event access and potential PEBS record loss") which moved the cpuc->events[idx] assignment out of x86_pmu_start() and into step 2 of x86_pmu_enable(), after the PERF_HES_ARCH check. This broke any path that calls pmu->start() without going through x86_pmu_enable() -- specifically the unthrottle path: perf_adjust_freq_unthr_events() -> perf_event_unthrottle_group() -> perf_event_unthrottle() -> event->pmu->start(event, 0) -> x86_pmu_start() // sets active_mask but not events[] The race sequence is: 1. A group of perf events overflows, triggering group throttle via perf_event_throttle_group(). All events are stopped: active_mask bits cleared, events[] preserved (x86_pmu_stop no longer clears events[] after commit 7e772a93eb61). 2. While still throttled (PERF_HES_STOPPED), x86_pmu_enable() runs due to other scheduling activity. Stopped events that need to move counters get PERF_HES_ARCH set and events[old_idx] cleared. In step 2 of x86_pmu_enable(), PERF_HES_ARCH causes these events to be skipped -- events[new_idx] is never set. 3. The timer tick unthrottles the group via pmu->start(). Since commit 7e772a93eb61 removed the events[] assignment from x86_pmu_start(), active_mask[new_idx] is set but events[new_idx] remains NULL. 4. A PMC overflow NMI fires. The handler iterates active counters, finds active_mask[2] set, reads events[2] which is NULL, and crashes dereferencing it. Move the cpuc->events[hwc->idx] assignment in x86_pmu_enable() to before the PERF_HES_ARCH check, so that events[] is populated even for events that are not immediately started. This ensures the unthrottle path via pmu->start() always finds a valid event pointer.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 6b089028bff1f2ff9e0c62b8f1faca1a620e5d6e , < 886fa869153917d902784098922defa20c3a2fe5 (git)
Affected: 7e772a93eb61cb6265bdd1c5bde17d0f2718b452 , < c1dd1e2b722d3f1f2e4977dad8d1be78fdfb30cb (git)
Affected: 7e772a93eb61cb6265bdd1c5bde17d0f2718b452 , < 8d5fae6011260de209aaf231120e8146b14bc8e0 (git)
Affected: cf69b99805c263117305ac6dffbc85aaf9259d32 (git)
Affected: 6.18.2 , < 6.18.20 (semver)
Affected: 6.17.13 , < 6.18 (semver)
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Linux Linux Affected: 6.19
Unaffected: 0 , < 6.19 (semver)
Unaffected: 6.18.20 , ≤ 6.18.* (semver)
Unaffected: 6.19.10 , ≤ 6.19.* (semver)
Unaffected: 7.0 , ≤ * (original_commit_for_fix)
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{
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nperf/x86: Move event pointer setup earlier in x86_pmu_enable()\n\nA production AMD EPYC system crashed with a NULL pointer dereference\nin the PMU NMI handler:\n\n  BUG: kernel NULL pointer dereference, address: 0000000000000198\n  RIP: x86_perf_event_update+0xc/0xa0\n  Call Trace:\n   \u003cNMI\u003e\n   amd_pmu_v2_handle_irq+0x1a6/0x390\n   perf_event_nmi_handler+0x24/0x40\n\nThe faulting instruction is `cmpq $0x0, 0x198(%rdi)` with RDI=0,\ncorresponding to the `if (unlikely(!hwc-\u003eevent_base))` check in\nx86_perf_event_update() where hwc = \u0026event-\u003ehw and event is NULL.\n\ndrgn inspection of the vmcore on CPU 106 showed a mismatch between\ncpuc-\u003eactive_mask and cpuc-\u003eevents[]:\n\n  active_mask: 0x1e (bits 1, 2, 3, 4)\n  events[1]:   0xff1100136cbd4f38  (valid)\n  events[2]:   0x0                 (NULL, but active_mask bit 2 set)\n  events[3]:   0xff1100076fd2cf38  (valid)\n  events[4]:   0xff1100079e990a90  (valid)\n\nThe event that should occupy events[2] was found in event_list[2]\nwith hw.idx=2 and hw.state=0x0, confirming x86_pmu_start() had run\n(which clears hw.state and sets active_mask) but events[2] was\nnever populated.\n\nAnother event (event_list[0]) had hw.state=0x7 (STOPPED|UPTODATE|ARCH),\nshowing it was stopped when the PMU rescheduled events, confirming the\nthrottle-then-reschedule sequence occurred.\n\nThe root cause is commit 7e772a93eb61 (\"perf/x86: Fix NULL event access\nand potential PEBS record loss\") which moved the cpuc-\u003eevents[idx]\nassignment out of x86_pmu_start() and into step 2 of x86_pmu_enable(),\nafter the PERF_HES_ARCH check. This broke any path that calls\npmu-\u003estart() without going through x86_pmu_enable() -- specifically\nthe unthrottle path:\n\n  perf_adjust_freq_unthr_events()\n    -\u003e perf_event_unthrottle_group()\n      -\u003e perf_event_unthrottle()\n        -\u003e event-\u003epmu-\u003estart(event, 0)\n          -\u003e x86_pmu_start()     // sets active_mask but not events[]\n\nThe race sequence is:\n\n  1. A group of perf events overflows, triggering group throttle via\n     perf_event_throttle_group(). All events are stopped: active_mask\n     bits cleared, events[] preserved (x86_pmu_stop no longer clears\n     events[] after commit 7e772a93eb61).\n\n  2. While still throttled (PERF_HES_STOPPED), x86_pmu_enable() runs\n     due to other scheduling activity. Stopped events that need to\n     move counters get PERF_HES_ARCH set and events[old_idx] cleared.\n     In step 2 of x86_pmu_enable(), PERF_HES_ARCH causes these events\n     to be skipped -- events[new_idx] is never set.\n\n  3. The timer tick unthrottles the group via pmu-\u003estart(). Since\n     commit 7e772a93eb61 removed the events[] assignment from\n     x86_pmu_start(), active_mask[new_idx] is set but events[new_idx]\n     remains NULL.\n\n  4. A PMC overflow NMI fires. The handler iterates active counters,\n     finds active_mask[2] set, reads events[2] which is NULL, and\n     crashes dereferencing it.\n\nMove the cpuc-\u003eevents[hwc-\u003eidx] assignment in x86_pmu_enable() to\nbefore the PERF_HES_ARCH check, so that events[] is populated even\nfor events that are not immediately started. This ensures the\nunthrottle path via pmu-\u003estart() always finds a valid event pointer."
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        },
        {
          "url": "https://git.kernel.org/stable/c/8d5fae6011260de209aaf231120e8146b14bc8e0"
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      ],
      "title": "perf/x86: Move event pointer setup earlier in x86_pmu_enable()",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-23435",
    "datePublished": "2026-04-03T15:15:20.465Z",
    "dateReserved": "2026-01-13T15:37:46.017Z",
    "dateUpdated": "2026-05-23T16:04:50.015Z",
    "state": "PUBLISHED"
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This broke any path that calls\\npmu-\u003estart() without going through x86_pmu_enable() -- specifically\\nthe unthrottle path:\\n\\n  perf_adjust_freq_unthr_events()\\n    -\u003e perf_event_unthrottle_group()\\n      -\u003e perf_event_unthrottle()\\n        -\u003e event-\u003epmu-\u003estart(event, 0)\\n          -\u003e x86_pmu_start()     // sets active_mask but not events[]\\n\\nThe race sequence is:\\n\\n  1. A group of perf events overflows, triggering group throttle via\\n     perf_event_throttle_group(). All events are stopped: active_mask\\n     bits cleared, events[] preserved (x86_pmu_stop no longer clears\\n     events[] after commit 7e772a93eb61).\\n\\n  2. While still throttled (PERF_HES_STOPPED), x86_pmu_enable() runs\\n     due to other scheduling activity. Stopped events that need to\\n     move counters get PERF_HES_ARCH set and events[old_idx] cleared.\\n     In step 2 of x86_pmu_enable(), PERF_HES_ARCH causes these events\\n     to be skipped -- events[new_idx] is never set.\\n\\n  3. The timer tick unthrottles the group via pmu-\u003estart(). Since\\n     commit 7e772a93eb61 removed the events[] assignment from\\n     x86_pmu_start(), active_mask[new_idx] is set but events[new_idx]\\n     remains NULL.\\n\\n  4. A PMC overflow NMI fires. The handler iterates active counters,\\n     finds active_mask[2] set, reads events[2] which is NULL, and\\n     crashes dereferencing it.\\n\\nMove the cpuc-\u003eevents[hwc-\u003eidx] assignment in x86_pmu_enable() to\\nbefore the PERF_HES_ARCH check, so that events[] is populated even\\nfor events that are not immediately started. This ensures the\\nunthrottle path via pmu-\u003estart() always finds a valid event pointer.\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":5.5,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":3.6}]},\"weaknesses\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-476\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.17.13\",\"versionEndExcluding\":\"6.18\",\"matchCriteriaId\":\"7C298528-1754-41BD-B4E9-84A37AB7BA32\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.18.2\",\"versionEndExcluding\":\"6.18.20\",\"matchCriteriaId\":\"29896448-5F31-40A5-A909-2BC59D21590D\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.19.1\",\"versionEndExcluding\":\"6.19.10\",\"matchCriteriaId\":\"D70DEFFE-AC47-4F3A-A2B2-2D67AB4CF3C8\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:6.19:-:*:*:*:*:*:*\",\"matchCriteriaId\":\"35C8A871-4971-433E-A046-FC9F7B7D190A\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*\",\"matchCriteriaId\":\"F253B622-8837-4245-BCE5-A7BF8FC76A16\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*\",\"matchCriteriaId\":\"4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*\",\"matchCriteriaId\":\"F666C8D8-6538-46D4-B318-87610DE64C34\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*\",\"matchCriteriaId\":\"02259FDA-961B-47BC-AE7F-93D7EC6E90C2\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*\",\"matchCriteriaId\":\"58A9FEFF-C040-420D-8F0A-BFDAAA1DF258\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*\",\"matchCriteriaId\":\"1D2315C0-D46F-4F85-9754-F9E5E11374A6\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*\",\"matchCriteriaId\":\"512EE3A8-A590-4501-9A94-5D4B268D6138\"}]}]}],\"references\":[{\"url\":\"https://git.kernel.org/stable/c/886fa869153917d902784098922defa20c3a2fe5\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/8d5fae6011260de209aaf231120e8146b14bc8e0\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/c1dd1e2b722d3f1f2e4977dad8d1be78fdfb30cb\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]}]}}"
  }
}


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