[PATCH 3/3] KVM: X86: Don't report L2 emulation failures to user-space

[Joerg Roedel <joerg.roedel@amd.com>]

This patch prevents that emulation failures which result
from emulating an instruction for an L2-Guest results in
being reported to userspace.
Without this patch a malicious L2-Guest would be able to
kill the L1 by triggering a race-condition between an vmexit
and the instruction emulator.
With this patch the L2 will most likely only kill itself in
this situation.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
---
 arch/x86/kvm/x86.c |   14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 410d2d1..4337a8b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4320,13 +4320,19 @@ EXPORT_SYMBOL_GPL(kvm_inject_realmode_interrupt);
 
 static int handle_emulation_failure(struct kvm_vcpu *vcpu)
 {
+	int r = EMULATE_DONE;
+
 	++vcpu->stat.insn_emulation_fail;
 	trace_kvm_emulate_insn_failed(vcpu);
-	vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
-	vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
-	vcpu->run->internal.ndata = 0;
+	if (!is_guest_mode(vcpu)) {
+		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+		vcpu->run->internal.ndata = 0;
+		r = EMULATE_FAIL;
+	}
 	kvm_queue_exception(vcpu, UD_VECTOR);
-	return EMULATE_FAIL;
+
+	return r;
 }
 
 static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t gva)
-- 
1.7.1