Commit c300aa64 authored Mar 11, 2013 by Andy Honig Committed by Marcelo Tosatti Mar 19, 2013

KVM: x86: fix for buffer overflow in handling of MSR_KVM_SYSTEM_TIME (CVE-2013-1796)



If the guest sets the GPA of the time_page so that the request to update the
time straddles a page then KVM will write onto an incorrect page.  The
write is done byusing kmap atomic to get a pointer to the page for the time
structure and then performing a memcpy to that page starting at an offset
that the guest controls.  Well behaved guests always provide a 32-byte aligned
address, however a malicious guest could use this to corrupt host kernel
memory.

Tested: Tested against kvmclock unit test.

Signed-off-by: Andrew Honig <ahonig@google.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

parent c09664bb

arch/x86/kvm/x86.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -1959,6 +1959,11 @@ int kvm_set_msr_common(struct kvm_vcpu vcpu, struct msr_data msr_info)
		/* ...but clean it before doing the actual write */
		vcpu->arch.time_offset = data & ~(PAGE_MASK \| 1);

		/* Check that the address is 32-byte aligned. */
		if (vcpu->arch.time_offset &
		(sizeof(struct pvclock_vcpu_time_info) - 1))
		break;

		vcpu->arch.time_page =
		gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT);