KVM: nSVM: always intercept VMLOAD/VMSAVE when nested (CVE-2021-3656)

KVM: nSVM: always intercept VMLOAD/VMSAVE when nested (CVE-2021-3656)

Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit?id=3dc5666baf2a135f250e4101d41d5959ac2c2e1f
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2021-3656

commit c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc upstream.

If L1 disables VMLOAD/VMSAVE intercepts, and doesn't enable
Virtual VMLOAD/VMSAVE (currently not supported for the nested hypervisor),
then VMLOAD/VMSAVE must operate on the L1 physical memory, which is only
possible by making L0 intercept these instructions.

Failure to do so allowed the nested guest to run VMLOAD/VMSAVE unintercepted,
and thus read/write portions of the host physical memory.

Fixes: 89c8a4984fc9 ("KVM: SVM: Enable Virtual VMLOAD VMSAVE feature")
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Gbp-Pq: Topic bugfix/x86
Gbp-Pq: Name KVM-nSVM-always-intercept-VMLOAD-VMSAVE-when-nested-.patch