Linux had a bug that could leave the Branch History Injection (BHI) Spectre-style mitigation switched off when it was needed, Phoronix reports. Debian developer Breno Leitao found it.
The gist
The mitigation was only turned on for the guest-to-host attack vector. So a kernel built without KVM, or booted with certain mitigation options, could lose BHI protection between user space and the kernel on affected Intel CPUs, which was never the intent.
What to do
The fix is going into Linux 7.4-rc2 and is tagged for backport to stable kernels going back to 2022. Install your distro’s kernel updates when they land, especially if you build custom kernels without KVM.
God Bless, and May the Source Be with You!
