From c300aa64ddf57d9c5d9c898a64b36877345dd4a9 Mon Sep 17 00:00:00 2001 From: Andy Honig Date: Mon, 11 Mar 2013 09:34:52 -0700 Subject: [PATCH] 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 Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/x86.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index f7c850b..2ade60c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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); -- 2.7.4