KVM: x86: Disallow hypercalls for guest callers in rings > 0

So far unprivileged guest callers running in ring 3 can issue, e.g., MMU
hypercalls. Normally, such callers cannot provide any hand-crafted MMU
command structure as it has to be passed by its physical address, but
they can still crash the guest kernel by passing random addresses.

To close the hole, this patch considers hypercalls valid only if issued
from guest ring 0. This may still be relaxed on a per-hypercall base in
the future once required.

Cc: stable@kernel.org
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/kvm_para.h b/include/linux/kvm_para.h
index 3ddce03766ca..d73109243fda 100644
--- a/include/linux/kvm_para.h
+++ b/include/linux/kvm_para.h
@@ -13,6 +13,7 @@
 #define KVM_ENOSYS              1000
 #define KVM_EFAULT              EFAULT
 #define KVM_E2BIG               E2BIG
+#define KVM_EPERM               EPERM
 
 #define KVM_HC_VAPIC_POLL_IRQ           1
 #define KVM_HC_MMU_OP                   2