| From | Ben Hutchings <> | Date | Mon, 22 Apr 2013 15:25:59 +0100 | Subject | [71/75] KVM: x86: fix for buffer overflow in handling of MSR_KVM_SYSTEM_TIME (CVE-2013-1796) |
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3.2.44-rc1 review patch. If anyone has any objections, please let me know.
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From: Andy Honig <ahonig@google.com>
commit c300aa64ddf57d9c5d9c898a64b36877345dd4a9 upstream.
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> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- arch/x86/kvm/x86.c | 5 +++++ 1 file changed, 5 insertions(+)
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1603,6 +1603,11 @@ int kvm_set_msr_common(struct kvm_vcpu * /* ...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);
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