From: Andy Honig Date: Mon, 11 Mar 2013 16:34:52 +0000 (-0700) Subject: KVM: x86: fix for buffer overflow in handling of MSR_KVM_SYSTEM_TIME (CVE-2013-1796) X-Git-Tag: v2.6.34.15~99 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1c46ee51d3f9aa8061c7db55b1b70d08db440862;p=thirdparty%2Fkernel%2Fstable.git KVM: x86: fix for buffer overflow in handling of MSR_KVM_SYSTEM_TIME (CVE-2013-1796) 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 Signed-off-by: Marcelo Tosatti Signed-off-by: Paul Gortmaker --- diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c1e586d82c1d4..65f9c0c45312b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1152,6 +1152,11 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data) /* ...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);