From 290b4bb1e3b871f5c0842a3c8f7e1059238cb56d Mon Sep 17 00:00:00 2001
From: Eduardo Habkost <ehabkost@redhat.com>
Date: Mon, 21 Sep 2009 14:25:19 -0300
Subject: [PATCH 2/3] KVM: x86: Disallow hypercalls for guest callers in rings > 0

RH-Author: Marcelo Tosatti <mtosatti@redhat.com>
Message-id: <20090918045402.GA30186@amt.cnet>
Patchwork-id: 3441
O-Subject: [RHEL-5.4.z KVM PATCH] KVM: x86: Disallow hypercalls for guest
	callers in rings > 0
Bugzilla: 524126
RH-Acked-by: Juan Quintela <quintela@redhat.com>
RH-Acked-by: Eduardo Habkost <ehabkost@redhat.com>
RH-Acked-by: Zachary Amsden <zamsden@redhat.com>
RH-Acked-by: Andrea Arcangeli <aarcange@redhat.com>

From: Jan Kiszka <jan.kiszka@siemens.com>

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>
(cherry picked from commit 07708c4af1346ab1521b26a202f438366b7bcffd)
Bugzilla: 524125

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 arch/x86/kvm/x86.c       |    6 ++++++
 include/linux/kvm_para.h |    1 +
 2 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8766325..93b8841 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2749,6 +2749,11 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 		a3 &= 0xFFFFFFFF;
 	}
 
+	if (kvm_x86_ops->get_cpl(vcpu) != 0) {
+		ret = -KVM_EPERM;
+		goto out;
+	}
+
 	switch (nr) {
 	case KVM_HC_VAPIC_POLL_IRQ:
 		ret = 0;
@@ -2760,6 +2765,7 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 		ret = -KVM_ENOSYS;
 		break;
 	}
+out:
 	kvm_register_write(vcpu, VCPU_REGS_RAX, ret);
 	++vcpu->stat.hypercalls;
 	return r;
diff --git a/include/linux/kvm_para.h b/include/linux/kvm_para.h
index 3ddce03..d731092 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
-- 
1.6.3.rc4.29.g8146