Bug 2301491 (CVE-2024-42126)

Summary: CVE-2024-42126 kernel: powerpc: Avoid nmi_enter/nmi_exit in real mode interrupt.
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: dfreiber, drow, jburrell, vkumar
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Fixed In Version: kernel 6.1.98, kernel 6.6.39, kernel 6.9.9, kernel 6.10 Doc Type: If docs needed, set a value
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On: 2301806    
Bug Blocks:    

Description OSIDB Bzimport 2024-07-30 08:34:29 UTC 
In the Linux kernel, the following vulnerability has been resolved:

powerpc: Avoid nmi_enter/nmi_exit in real mode interrupt.

nmi_enter()/nmi_exit() touches per cpu variables which can lead to kernel
crash when invoked during real mode interrupt handling (e.g. early HMI/MCE
interrupt handler) if percpu allocation comes from vmalloc area.

Early HMI/MCE handlers are called through DEFINE_INTERRUPT_HANDLER_NMI()
wrapper which invokes nmi_enter/nmi_exit calls. We don't see any issue when
percpu allocation is from the embedded first chunk. However with
CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK enabled there are chances where percpu
allocation can come from the vmalloc area.

With kernel command line "percpu_alloc=page" we can force percpu allocation
to come from vmalloc area and can see kernel crash in machine_check_early:

[    1.215714] NIP [c000000000e49eb4] rcu_nmi_enter+0x24/0x110
[    1.215717] LR [c0000000000461a0] machine_check_early+0xf0/0x2c0
[    1.215719] --- interrupt: 200
[    1.215720] [c000000fffd73180] [0000000000000000] 0x0 (unreliable)
[    1.215722] [c000000fffd731b0] [0000000000000000] 0x0
[    1.215724] [c000000fffd73210] [c000000000008364] machine_check_early_common+0x134/0x1f8

Fix this by avoiding use of nmi_enter()/nmi_exit() in real mode if percpu
first chunk is not embedded.
Comment 1 Mauro Matteo Cascella 2024-07-30 19:38:43 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2024073026-CVE-2024-42126-fdab@gregkh/T
Comment 2 Mauro Matteo Cascella 2024-07-30 19:39:03 UTC 
Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 2301806]