Bug 2525459 (CVE-2026-80626)

Summary: CVE-2026-80626 kernel: powerpc/perf: fix preempt count underflow in fsl_emb_pmu_del
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's powerpc/perf component. An issue in the `fsl_emb_pmu_del()` function can lead to a preempt count underflow. This occurs when the function attempts to decrement a preemption counter without a corresponding increment, specifically when `event->hw.idx` is negative. On systems configured for preemption, this underflow can result in a 'scheduling while atomic' bug, leading to a system crash and a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-08-28 07:46:05 UTC 
In the Linux kernel, the following vulnerability has been resolved:

powerpc/perf: fix preempt count underflow in fsl_emb_pmu_del

fsl_emb_pmu_del() unconditionally calls put_cpu_var(cpu_hw_events) at
the 'out:' label, but only calls the matching get_cpu_var() after the
'i < 0' early-return check. When event->hw.idx is negative the
function jumps to 'out:' without having taken get_cpu_var(), and the
trailing put_cpu_var() then issues an unmatched preempt_enable(),
underflowing preempt_count.

On a CONFIG_PREEMPT=y kernel preempt_count would underflow and
eventually present as a 'scheduling while atomic' BUG.

Move put_cpu_var() to pair with get_cpu_var() so the percpu access is
correctly bracketed and the 'out:' label only handles perf_pmu_enable.
Comment 1 gkamathe 2026-09-01 06:13:54 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082837-CVE-2026-80626-26f8@gregkh/T