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Subject[6/8] KVM: x86: Disallow hypercalls for guest callers in rings > 0 [CVE-2009-3290]
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From: Jan Kiszka <jan.kiszka@siemens.com>

[ backport to 2.6.27 by Chuck Ebbert <cebbert@redhat.com> ]

commit 07708c4af1346ab1521b26a202f438366b7bcffd upstream.

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.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/x86/kvm/x86.c | 6 ++++++
include/linux/kvm_para.h | 1 +
2 files changed, 7 insertions(+)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2571,6 +2571,11 @@ int kvm_emulate_hypercall(struct kvm_vcp
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;
@@ -2582,6 +2587,7 @@ int kvm_emulate_hypercall(struct kvm_vcp
ret = -KVM_ENOSYS;
break;
}
+out:
vcpu->arch.regs[VCPU_REGS_RAX] = ret;
kvm_x86_ops->decache_regs(vcpu);
++vcpu->stat.hypercalls;
--- 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



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