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

Vulnerability from cvelistv5 – Published: 2024-05-22 06:19 – Updated: 2025-05-04 12:41
VLAI?
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
References
Impacted products
Vendor Product Version
Linux Linux Affected: bdf4d33e8342b90386156204e1da0cdfdb4bf146 , < 53770a411559cf7bc0906d1df319cc533d2f4f58 (git)
Affected: 2c669ef6979c370f98d4b876e54f19613c81e075 , < 3ea0b497a7a2fff6a4b7090310c9f52c91975934 (git)
Affected: 2c669ef6979c370f98d4b876e54f19613c81e075 , < 787252a10d9422f3058df9a4821f389e5326c440 (git)
Affected: 2b6148ef2bd6d8ddc76e7873114f7769b6aa25f0 (git)
Affected: 20a015e948b825afb47855de2efce7cae7c2608f (git)
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    Linux 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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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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