KVM: VMX: fix vmx null pointer dereference on debug register access

There is a bug in KVM that can be used to crash a host on Intel
machines. If emulator is tricked into emulating mov to/from DR instruction
it causes NULL pointer dereference on VMX since kvm_x86_ops->(set|get)_dr
are not initialized. Recently this is not exploitable from guest
userspace, but malicious guest kernel can trigger it easily.

CVE-2010-0435

On upstream bug was fixed differently around 2.6.34.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 724a6ad08643c708724ea318784d6d36dfa3fa34..0990f0a459d6baa038e523be7f110dff8c75080c 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2782,6 +2782,9 @@ int emulator_get_dr(struct x86_emulate_ctxt *ctxt, int dr, unsigned long *dest)
 {
        struct kvm_vcpu *vcpu = ctxt->vcpu;
 
+       if (!kvm_x86_ops->get_dr)
+               return X86EMUL_UNHANDLEABLE;
+
        switch (dr) {
        case 0 ... 3:
                *dest = kvm_x86_ops->get_dr(vcpu, dr);
@@ -2797,6 +2800,9 @@ int emulator_set_dr(struct x86_emulate_ctxt *ctxt, int dr, unsigned long value)
        unsigned long mask = (ctxt->mode == X86EMUL_MODE_PROT64) ? ~0ULL : ~0U;
        int exception;
 
+       if (!kvm_x86_ops->set_dr)
+               return X86EMUL_UNHANDLEABLE;
+
        kvm_x86_ops->set_dr(ctxt->vcpu, dr, value & mask, &exception);
        if (exception) {
                /* FIXME: better handling */