CVE-2026-43331

Summary

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

x86/kexec: Disable KCOV instrumentation after load_segments()

The load_segments() function changes segment registers, invalidating GS base (which KCOV relies on for per-cpu data). When CONFIG_KCOV is enabled, any subsequent instrumented C code call (e.g. native_gdt_invalidate()) 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 CONFIG_KEXEC and CONFIG_KCOV to be enabled simultaneously.

Adding safeguards directly to the KCOV fast-path (__sanitizer_cov_trace_pc()) 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 machine_kexec_64.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 CONFIG_KCOV is not supported there.

[ bp: Space out comment for better readability. ]

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/0e96cd314c0d819c1635d68125a4d77852c2162e
• https://git.kernel.org/stable/c/593d67032544b9271094fc9b43e437e017cb2b2f
• https://git.kernel.org/stable/c/1e3e98596c2769721ade0418434852fb3af4849a
• https://git.kernel.org/stable/c/de05c66fab8847237a9ca216934e56d3ee837f08
• https://git.kernel.org/stable/c/917e3ad3321e75ca0223d5ccf26ceda116aa51e1

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