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CVE-2026-89460

Status: ReceivedUnscored—

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

s390/cpum_cf: Handle CPU hotplug via prepare/dead callbacks

The command 'perf stat -e cycles -- <command>' crashes the kernel when CPUs are hotplug added during that run.

Root cause is the allocation of struct cpu_cf_events at first event initialization. The allocation is dynamic and the first event that has task context creates such a structure for each online CPU. This is not sufficient. CPUs may be offline during event creation and can be set online during the perf run time. For example commands

# echo 0 > /sys/devices/system/cpu/cpu1/online # perf stat -e cycles -i -- stress-ng -t10s --matrix X # sleep 1 # echo 1 > /sys/devices/system/cpu/cpu1/online

Read full descriptionShow less

create an event for CPUs 0,2-X. Since the events are created with task-context, the scheduler will eventually schedule the program on CPU1. This CPU has not created and initialized any per CPU event infrastructure as that CPU was not online at the time of the perf invocation. Thus when the scheduler runs stress-ng on CPU1, the function cpumf_pmu_add() refers to a NULL pointer:

This function call is invoked after the task stress-ng has been made runnable on CPU1. And this_cpu_cfhw() returns NULL.

The issue arises only in per-task context when the CPUMF facility is used and the scheduler picks a random CPU for such a process to run on. The scheduler enables the CPUMF infrastructure via PMU callback functions pmu::add() and pmu::del().

Introduce a CPU hotplug prepare/dead callback pair which creates and removes the per CPU counter data while the CPU is offline. Count the users which track every CPU (cpu == -1), that is perf_event_open() events with task context and /dev/hwctr device sessions, in the new counter cpu_cf_root::tskcnt, protected by pmc_reserve_mutex. This ensures the infrastructure is available when new CPU is selected to run the per-task context process.

In cpum_cf_free_root() and cpum_cf_free_cpu() ensure the reference pointer to data structures is set to NULL before the data is freed to prevent interrupt handlers to access stale data.

[gor@linux.ibm.com: change commit message]

Technical details traces, logs and code from the original report
 struct cpu_cf_events *cpuhw = this_cpu_cfhw();

The result is a panic:
Unable to handle kernel pointer dereference in virtual kernel address space
Failing address: 0000000000000000 TEID: 0000000000000483
....
Krnl PSW : 0404d00180000000 000003ef8291fd0c (cpumf_pmu_add+0x3c/0x80)
....
Call Trace:
 [<000003ef8291fd0c>] cpumf_pmu_add+0x3c/0x80
 [<000003ef82bb5e3e>] event_sched_in+0xae/0x190
 [<000003ef82bb60d6>] merge_sched_in+0x1b6/0x390
 [<000003ef82bb65b8>] visit_groups_merge.constprop.0.isra.0+0x308/0x5b0
 [<000003ef82bb689a>] pmu_groups_sched_in+0x3a/0x50
 [<000003ef82bb6a30>] ctx_sched_in+0x180/0x260
 [<000003ef82bb780c>] perf_event_context_sched_in+0x11c/0x2d0
 [<000003ef82bb79ee>] __perf_event_task_sched_in+0x2e/0xc0
 [<000003ef82994834>] finish_task_switch.isra.0+0x1a4/0x250
....
Last Breaking-Event-Address:
 [<000003ef8291f1d8>] this_cpu_cfhw+0x38/0x40

CVSS

NVD hasn't assigned a CVSS score to this CVE (common since the April 2026 policy change).

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

Affected technologies (1)

⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.

Linux — Linux KernelAI

References

Raw JSON (NVD)

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{
  "id": "CVE-2026-89460",
  "cveTags": [],
  "metrics": {},
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "9b9cf3c77e7e090b30657b3d2c288deb58dfb4f2",
              "lessThan": "991be92489bc7b1b6e7903debb96bd58c892dee4",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "9b9cf3c77e7e090b30657b3d2c288deb58dfb4f2",
              "lessThan": "777d040c2f91d8d929b4a32333dfe4102b27caea",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "9b9cf3c77e7e090b30657b3d2c288deb58dfb4f2",
              "lessThan": "dcce7a06ea690d5cf46a705a9b74cf0398ac091f",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "9b9cf3c77e7e090b30657b3d2c288deb58dfb4f2",
              "lessThan": "71d46de9153e067c63a15f3b00e6364e1c0230f8",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "9b9cf3c77e7e090b30657b3d2c288deb58dfb4f2",
              "lessThan": "337bd95507a16063687cfc286ea90de5cca48c37",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "arch/s390/kernel/perf_cpum_cf.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.5"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "6.5",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
              "status": "unaffected",
              "version": "6.12.109",
              "versionType": "semver",
              "lessThanOrEqual": "6.12.*"
            },
            {
              "status": "unaffected",
              "version": "6.18.50",
              "versionType": "semver",
              "lessThanOrEqual": "6.18.*"
            },
            {
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver",
              "lessThanOrEqual": "7.2.*"
            },
            {
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "arch/s390/kernel/perf_cpum_cf.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-09-11T20:19:26.893",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/337bd95507a16063687cfc286ea90de5cca48c37",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/71d46de9153e067c63a15f3b00e6364e1c0230f8",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/777d040c2f91d8d929b4a32333dfe4102b27caea",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/991be92489bc7b1b6e7903debb96bd58c892dee4",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/dcce7a06ea690d5cf46a705a9b74cf0398ac091f",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ns390/cpum_cf: Handle CPU hotplug via prepare/dead callbacks\n\nThe command 'perf stat -e cycles -- <command>' crashes the kernel\nwhen CPUs are hotplug added during that run.\n\nRoot cause is the allocation of struct cpu_cf_events at first\nevent initialization. The allocation is dynamic and the first\nevent that has task context creates such a structure for\neach online CPU. This is not sufficient. CPUs may be offline\nduring event creation and can be set online during the\nperf run time. For example commands\n\n # echo 0 > /sys/devices/system/cpu/cpu1/online\n # perf stat -e cycles -i -- stress-ng -t10s --matrix X\n # sleep 1\n # echo 1 > /sys/devices/system/cpu/cpu1/online\n\ncreate an event for CPUs 0,2-X. Since the events are created with\ntask-context, the scheduler will eventually schedule the program\non CPU1. This CPU has not created and initialized any per\nCPU event infrastructure as that CPU was not online at the time\nof the perf invocation. Thus when the scheduler runs stress-ng\non CPU1, the function cpumf_pmu_add() refers to a NULL pointer:\n\n struct cpu_cf_events *cpuhw = this_cpu_cfhw();\n\nThis function call is invoked after the task stress-ng has been\nmade runnable on CPU1. And this_cpu_cfhw() returns NULL.\n\nThe result is a panic:\nUnable to handle kernel pointer dereference in virtual kernel address space\nFailing address: 0000000000000000 TEID: 0000000000000483\n....\nKrnl PSW : 0404d00180000000 000003ef8291fd0c (cpumf_pmu_add+0x3c/0x80)\n....\nCall Trace:\n [<000003ef8291fd0c>] cpumf_pmu_add+0x3c/0x80\n [<000003ef82bb5e3e>] event_sched_in+0xae/0x190\n [<000003ef82bb60d6>] merge_sched_in+0x1b6/0x390\n [<000003ef82bb65b8>] visit_groups_merge.constprop.0.isra.0+0x308/0x5b0\n [<000003ef82bb689a>] pmu_groups_sched_in+0x3a/0x50\n [<000003ef82bb6a30>] ctx_sched_in+0x180/0x260\n [<000003ef82bb780c>] perf_event_context_sched_in+0x11c/0x2d0\n [<000003ef82bb79ee>] __perf_event_task_sched_in+0x2e/0xc0\n [<000003ef82994834>] finish_task_switch.isra.0+0x1a4/0x250\n....\nLast Breaking-Event-Address:\n [<000003ef8291f1d8>] this_cpu_cfhw+0x38/0x40\n\nThe issue arises only in per-task context when the CPUMF facility is\nused and the scheduler picks a random CPU for such a process to run on.\nThe scheduler enables the CPUMF infrastructure via PMU callback\nfunctions pmu::add() and pmu::del().\n\nIntroduce a CPU hotplug prepare/dead callback pair which creates and\nremoves the per CPU counter data while the CPU is offline. Count the\nusers which track every CPU (cpu == -1), that is perf_event_open()\nevents with task context and /dev/hwctr device sessions, in the new\ncounter cpu_cf_root::tskcnt, protected by pmc_reserve_mutex.\nThis ensures the infrastructure is available when\nnew CPU is selected to run the per-task context process.\n\nIn cpum_cf_free_root() and cpum_cf_free_cpu() ensure the reference\npointer to data structures is set to NULL before the data is freed\nto prevent interrupt handlers to access stale data.\n\n[gor@linux.ibm.com: change commit message]"
    }
  ],
  "lastModified": "2026-09-14T13:19:02.357",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}