Commit c300aa64 authored by Andy Honig's avatar Andy Honig Committed by Marcelo Tosatti

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: default avatarAndrew Honig <ahonig@google.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent c09664bb
...@@ -1959,6 +1959,11 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) ...@@ -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 */ /* ...but clean it before doing the actual write */
vcpu->arch.time_offset = data & ~(PAGE_MASK | 1); 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 = vcpu->arch.time_page =
gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT); gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT);
......
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