On Fri, Jul 21, 2023 at 09:51:16PM -0700, Michael Kelley wrote: > On hardware that supports Indirect Branch Tracking (IBT), Hyper-V VMs > with ConfigVersion 9.3 or later support IBT in the guest. However, > current versions of Hyper-V have a bug in that there's not an ENDBR64 > instruction at the beginning of the hypercall page. Since hypercalls are > made with an indirect call to the hypercall page, all hypercall attempts > fail with an exception and Linux panics. > > A Hyper-V fix is in progress to add ENDBR64. But guard against the Linux > panic by clearing X86_FEATURE_IBT if the hypercall page doesn't start > with ENDBR. The VM will boot and run without IBT. > > If future Linux 32-bit kernels were to support IBT, additional hypercall > page hackery would be needed to make IBT work for such kernels in a > Hyper-V VM. > > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx> Applied to hyperv-fixes. Thanks.
