perf/x86: Move event pointer setup earlier in x86_pmu_enable()

{
  "id": "b825c3d0793deb80b672fe55d5232e90228c9c41404c7a3fb5e989083e4cea7b",
  "url": "https://osv.dev/vulnerability/CVE-2026-23435",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "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: 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_pm",
    "evidence": "osv:CVE-2026-23435",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.20",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.10",
            "evidence": "/affected/1/ranges"
          }
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        "affected_versions": []
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    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-23435",
      "aliases": [
        "CVE-2026-23435"
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      ],
      "modified": "2026-10-28T02:30:32.421111314Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/886fa869153917d902784098922defa20c3a2fe5",
        "https://git.kernel.org/stable/c/8d5fae6011260de209aaf231120e8146b14bc8e0",
        "https://git.kernel.org/stable/c/c1dd1e2b722d3f1f2e4977dad8d1be78fdfb30cb",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23435.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-23435",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
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        "value": "CVE-2026-23435",
        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": null
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  "source_id": "core-osv",
  "document_id": 499329,
  "published_at": "2026-04-03T15:15:20.465+00:00"
}