CVE-2026-43331: x86/kexec: Disable KCOV instrumentation after load_segments()
In the Linux kernel, the following vulnerability has been resolved:
x86/kexec: Disable KCOV instrumentation after loadsegments()
The loadsegments() function changes segment registers, invalidating GS base (which KCOV relies on for per-cpu data). When CONFIGKCOV is enabled, any subsequent instrumented C code call (e.g. nativegdtinvalidate()) begins crashing the kernel in an endless loop.
To reproduce the problem, it's sufficient to do kexec on a KCOV-instrumented kernel:
$ kexec -l /boot/otherKernel $ kexec -e
The real-world context for this problem is enabling crash dump collection in syzkaller. For this, the tool loads a panic kernel before fuzzing and then calls makedumpfile after the panic. This workflow requires both CONFIGKEXEC and CONFIGKCOV to be enabled simultaneously.
Adding safeguards directly to the KCOV fast-path (sanitizercovtracepc()) is also undesirable as it would introduce an extra performance overhead.
Disabling instrumentation for the individual functions would be too fragile, so disable KCOV instrumentation for the entire machinekexec64.c and physaddr.c. If coverage-guided fuzzing ever needs these components in the future, other approaches should be considered.
The problem is not relevant for 32 bit kernels as CONFIGKCOV is not supported there.
[ bp: Space out comment for better readability. ]
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
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debian/linuxto a version that resolves this vulnerability.Fixed in 6.1.176-1Fixed in 6.1.190-1Fixed in 6.12.107-1Fixed in 6.12.116-1Fixed in 7.2.15-1Fixed in 7.3.3-1 - Upgrade
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ubuntu/linux-aws-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1066.69~22.04.1 - Upgrade
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ubuntu/linux-azure-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1070.78~22.04.1 - Upgrade
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ubuntu/linux-azure-fde-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1068.75~22.04.1 - Upgrade
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ubuntu/linux-gcp-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1070.78~22.04.1 - Upgrade
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ubuntu/linux-ibm-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1066.67~22.04.1 - Upgrade
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ubuntu/linux-lowlatency-hwe-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-146.146.1~22.04.1 - Upgrade
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ubuntu/linux-nvidia-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1064.67~22.04.1 - Upgrade
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ubuntu/linux-riscv-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-146.146~22.04.1 - Upgrade
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ubuntu/linux-realtime-6.8to a version that resolves this vulnerability.Fixed in 6.8.1-1061.62~22.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 6.8.0-146.146 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 6.8.0-1066.69 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 6.8.0-1070.78 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 6.8.0-1068.75 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 6.8.0-1070.78 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 6.8.0-1065.73 - Upgrade
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ubuntu/linux-gkeopto a version that resolves this vulnerability.Fixed in 6.8.0-1051.55 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 6.8.0-1066.67 - Upgrade
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ubuntu/linux-lowlatencyto a version that resolves this vulnerability.Fixed in 6.8.0-146.146.1 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 6.8.0-1064.67 - Upgrade
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ubuntu/linux-nvidia-lowlatencyto a version that resolves this vulnerability.Fixed in 6.8.0-1064.67.1 - Upgrade
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ubuntu/linux-nvidia-tegrato a version that resolves this vulnerability.Fixed in 6.8.0-1038.42 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 6.8.0-1063.66 - Upgrade
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ubuntu/linux-vmwareto a version that resolves this vulnerability.Fixed in 6.8.0-1008.8 - Upgrade
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ubuntu/linux-bluefieldto a version that resolves this vulnerability.Fixed in 6.8.0-1032.37 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 6.8.1-1061.62 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1066.69+fips1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1069.77+fips1 - Upgrade
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-146.146+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1070.78+fips1 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 7.0.0-1006.6 - Configuration
Disable KCOV instrumentation for the entire machine_kexec_64.c and physaddr.c files.
Linux kernel KCOV instrumentation KCOV instrumentation for machine_kexec_64.c and physaddr.c = disabled
Event History
Frequently Asked Questions
What is the severity of CVE-2026-43331?
CVE-2026-43331 has been classified with a moderate severity rating due to its potential impact on security within the Linux kernel.
How do I fix CVE-2026-43331?
To mitigate CVE-2026-43331, users should upgrade to the latest version of the Linux kernel where the vulnerability has been resolved.
Which versions of the Linux kernel are affected by CVE-2026-43331?
CVE-2026-43331 affects versions of the Linux kernel that utilize the x86_64 architecture, particularly prior to the patch.
What are the risks associated with CVE-2026-43331?
The primary risk associated with CVE-2026-43331 is the potential for exploitation that may lead to unauthorized access or control over system resources.
Does CVE-2026-43331 affect all Linux distributions?
CVE-2026-43331 impacts any Linux distributions that incorporate the vulnerable x86_64 kernel version unless patched.