Vulnerability-Lookup

GHSA-RCM4-5VXV-3G8Q

Vulnerability from github – Published: 2024-05-22 09:31 – Updated: 2025-09-29 18:33

Details

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

powerpc/smp: do not decrement idle task preempt count in CPU offline

With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we get:

BUG: scheduling while atomic: swapper/1/0/0x00000000 no locks held by swapper/1/0. CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100 Call Trace: dump_stack_lvl+0xac/0x108 __schedule_bug+0xac/0xe0 __schedule+0xcf8/0x10d0 schedule_idle+0x3c/0x70 do_idle+0x2d8/0x4a0 cpu_startup_entry+0x38/0x40 start_secondary+0x2ec/0x3a0 start_secondary_prolog+0x10/0x14

This is because powerpc's arch_cpu_idle_dead() decrements the idle task's preempt count, for reasons explained in commit a7c2bb8279d2 ("powerpc: Re-enable preemption before cpu_die()"), specifically "start_secondary() expects a preempt_count() of 0."

However, since commit 2c669ef6979c ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug") and commit f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled"), that justification no longer holds.

The idle task isn't supposed to re-enable preemption, so remove the vestigial preempt_enable() from the CPU offline path.

Tested with pseries and powernv in qemu, and pseries on PowerVM.

Severity ?

5.5 (Medium)


                  
                    CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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{
  "affected": [],
  "aliases": [
    "CVE-2021-47454"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2024-05-22T07:15:10Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\npowerpc/smp: do not decrement idle task preempt count in CPU offline\n\nWith PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we\nget:\n\nBUG: scheduling while atomic: swapper/1/0/0x00000000\nno locks held by swapper/1/0.\nCPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100\nCall Trace:\n dump_stack_lvl+0xac/0x108\n __schedule_bug+0xac/0xe0\n __schedule+0xcf8/0x10d0\n schedule_idle+0x3c/0x70\n do_idle+0x2d8/0x4a0\n cpu_startup_entry+0x38/0x40\n start_secondary+0x2ec/0x3a0\n start_secondary_prolog+0x10/0x14\n\nThis is because powerpc\u0027s arch_cpu_idle_dead() decrements the idle task\u0027s\npreempt count, for reasons explained in commit a7c2bb8279d2 (\"powerpc:\nRe-enable preemption before cpu_die()\"), specifically \"start_secondary()\nexpects a preempt_count() of 0.\"\n\nHowever, since commit 2c669ef6979c (\"powerpc/preempt: Don\u0027t touch the idle\ntask\u0027s preempt_count during hotplug\") and commit f1a0a376ca0c (\"sched/core:\nInitialize the idle task with preemption disabled\"), that justification no\nlonger holds.\n\nThe idle task isn\u0027t supposed to re-enable preemption, so remove the\nvestigial preempt_enable() from the CPU offline path.\n\nTested with pseries and powernv in qemu, and pseries on PowerVM.",
  "id": "GHSA-rcm4-5vxv-3g8q",
  "modified": "2025-09-29T18:33:07Z",
  "published": "2024-05-22T09:31:45Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-47454"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3ea0b497a7a2fff6a4b7090310c9f52c91975934"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/53770a411559cf7bc0906d1df319cc533d2f4f58"
    },
    {
      "type": "WEB",
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    }
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  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2021-47454 (GCVE-0-2021-47454)

Vulnerability from cvelistv5 – Published: 2024-05-22 06:19 – Updated: 2025-05-04 12:41

Title

powerpc/smp: do not decrement idle task preempt count in CPU offline

Summary

In the Linux kernel, the following vulnerability has been resolved: powerpc/smp: do not decrement idle task preempt count in CPU offline With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we get: BUG: scheduling while atomic: swapper/1/0/0x00000000 no locks held by swapper/1/0. CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100 Call Trace: dump_stack_lvl+0xac/0x108 __schedule_bug+0xac/0xe0 __schedule+0xcf8/0x10d0 schedule_idle+0x3c/0x70 do_idle+0x2d8/0x4a0 cpu_startup_entry+0x38/0x40 start_secondary+0x2ec/0x3a0 start_secondary_prolog+0x10/0x14 This is because powerpc's arch_cpu_idle_dead() decrements the idle task's preempt count, for reasons explained in commit a7c2bb8279d2 ("powerpc: Re-enable preemption before cpu_die()"), specifically "start_secondary() expects a preempt_count() of 0." However, since commit 2c669ef6979c ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug") and commit f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled"), that justification no longer holds. The idle task isn't supposed to re-enable preemption, so remove the vestigial preempt_enable() from the CPU offline path. Tested with pseries and powernv in qemu, and pseries on PowerVM.

Severity ?

No CVSS data available.

Assigner

Linux

References

URL

Tags

	https://git.kernel.org/stable/c/53770a411559cf7bc…
	https://git.kernel.org/stable/c/3ea0b497a7a2fff6a…
	https://git.kernel.org/stable/c/787252a10d9422f30…

Impacted products

Vendor

Product

Version

Linux

Affected: bdf4d33e8342b90386156204e1da0cdfdb4bf146 , < 53770a411559cf7bc0906d1df319cc533d2f4f58 (git)
Affected: 2c669ef6979c370f98d4b876e54f19613c81e075 , < 3ea0b497a7a2fff6a4b7090310c9f52c91975934 (git)
Affected: 2c669ef6979c370f98d4b876e54f19613c81e075 , < 787252a10d9422f3058df9a4821f389e5326c440 (git)
Affected: 2b6148ef2bd6d8ddc76e7873114f7769b6aa25f0 (git)
Affected: 20a015e948b825afb47855de2efce7cae7c2608f (git)

Linux

Affected: 5.14
Unaffected: 0 , < 5.14 (semver)
Unaffected: 5.10.76 , ≤ 5.10.* (semver)
Unaffected: 5.14.15 , ≤ 5.14.* (semver)
Unaffected: 5.15 , ≤ * (original_commit_for_fix)

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Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-RCM4-5VXV-3G8Q

CVE-2021-47454 (GCVE-0-2021-47454)

Tags

Sightings

Nomenclature