Executive brief
A technical issue was identified in the Linux kernel's virtualization component (KVM) specifically affecting x86 systems. The issue involves how the system handles certain input/output operations between the virtual machine and the host hardware. While the fix improves code reliability and internal data handling, the developers noted no intended functional change, suggesting the practical risk to operations or data is minimal.
Technical details
A vulnerability in the Linux kernel's KVM x86 implementation was resolved by weaning 'fast IN' operations from emulator_pio_in(). The root cause was an indirect call path where emulator_pio_in() was used for fast PIO despite __emulator_pio_in() being more appropriate once it was updated to correctly fill the 'val' register during in-kernel PIO handling. The fix ensures that fast PIO bypasses the unnecessary logic in emulator_pio_in(), specifically where vcpu->arch.pio.count is expected to be zero. This is primarily a code refactoring and hardening fix to ensure consistent state handling during VM exits for I/O instructions. The issue was addressed in the Linux kernel stable tree.
Affected products
- Linux Linux Kernel 4.10 to 6.0
Timeline
- 2021-10-22: other: Patch authored
- 2022-06-24: patched: Patch committed to stable tree
- 2026-07-30: disclosed: CVE published