Harden KVM against goofy userspace by restricting the Xen hypercall MSR index to the de facto standard synthetic range, 0x40000000 - 0x4fffffff. This obviously has the potential to break userspace, but I'm fairly confident it'll be fine (knock wood), and doing nothing is not an option as letting userspace redirect any WRMSR is at best completely broken. Patches 2-5 are tangentially related cleanups. v2: - Collect reviews. [Paul, David] - Add proper #defines for the range. [David] - Drop the syzkaller/stable tags (rely on disallow host writes to fix the syzkaller splat]. David v1: https://lore.kernel.org/all/20250201011400.669483-1-seanjc@xxxxxxxxxx Sean Christopherson (5): KVM: x86/xen: Restrict hypercall MSR to unofficial synthetic range KVM: x86/xen: Add an #ifdef'd helper to detect writes to Xen MSR KVM: x86/xen: Consult kvm_xen_enabled when checking for Xen MSR writes KVM: x86/xen: Bury xen_hvm_config behind CONFIG_KVM_XEN=y KVM: x86/xen: Move kvm_xen_hvm_config field into kvm_xen arch/x86/include/asm/kvm_host.h | 4 ++-- arch/x86/include/uapi/asm/kvm.h | 3 +++ arch/x86/kvm/x86.c | 4 ++-- arch/x86/kvm/xen.c | 29 +++++++++++++++++++---------- arch/x86/kvm/xen.h | 17 +++++++++++++++-- 5 files changed, 41 insertions(+), 16 deletions(-) base-commit: 3617c0ee7decb3db3f230b1c844126575fab4d49 -- 2.48.1.601.g30ceb7b040-goog
