Commit 0b79459b authored by Andy Honig's avatar Andy Honig Committed by Marcelo Tosatti
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KVM: x86: Convert MSR_KVM_SYSTEM_TIME to use gfn_to_hva_cache functions (CVE-2013-1797) 



There is a potential use after free issue with the handling of
MSR_KVM_SYSTEM_TIME.  If the guest specifies a GPA in a movable or removable
memory such as frame buffers then KVM might continue to write to that
address even after it's removed via KVM_SET_USER_MEMORY_REGION.  KVM pins
the page in memory so it's unlikely to cause an issue, but if the user
space component re-purposes the memory previously used for the guest, then
the guest will be able to corrupt that 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 c300aa64

arch/x86/include/asm/kvm_host.h

+2 −2
Original line number Diff line number Diff line
@@ -414,8 +414,8 @@ struct kvm_vcpu_arch { 
	gpa_t time;

	struct pvclock_vcpu_time_info hv_clock;

	unsigned int hw_tsc_khz;

	unsigned int time_offset;

	struct page *time_page;

	struct gfn_to_hva_cache pv_time;

	bool pv_time_enabled;

	/* set guest stopped flag in pvclock flags field */

	bool pvclock_set_guest_stopped_request;

arch/x86/kvm/x86.c

+20 −27
Original line number Diff line number Diff line
@@ -1406,10 +1406,9 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) 
	unsigned long flags, this_tsc_khz;

	struct kvm_vcpu_arch *vcpu = &v->arch;

	struct kvm_arch *ka = &v->kvm->arch;

	void *shared_kaddr;

	s64 kernel_ns, max_kernel_ns;

	u64 tsc_timestamp, host_tsc;

	struct pvclock_vcpu_time_info *guest_hv_clock;

	struct pvclock_vcpu_time_info guest_hv_clock;

	u8 pvclock_flags;

	bool use_master_clock;
@@ -1463,7 +1462,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) 


	local_irq_restore(flags);



	if (!vcpu->time_page)

	if (!vcpu->pv_time_enabled)

		return 0;



	/*
@@ -1525,12 +1524,12 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) 
	 */

	vcpu->hv_clock.version += 2;



	shared_kaddr = kmap_atomic(vcpu->time_page);



	guest_hv_clock = shared_kaddr + vcpu->time_offset;

	if (unlikely(kvm_read_guest_cached(v->kvm, &vcpu->pv_time,

		&guest_hv_clock, sizeof(guest_hv_clock))))

		return 0;



	/* retain PVCLOCK_GUEST_STOPPED if set in guest copy */

	pvclock_flags = (guest_hv_clock->flags & PVCLOCK_GUEST_STOPPED);

	pvclock_flags = (guest_hv_clock.flags & PVCLOCK_GUEST_STOPPED);



	if (vcpu->pvclock_set_guest_stopped_request) {

		pvclock_flags |= PVCLOCK_GUEST_STOPPED;
@@ -1543,12 +1542,9 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) 


	vcpu->hv_clock.flags = pvclock_flags;



	memcpy(shared_kaddr + vcpu->time_offset, &vcpu->hv_clock,

	kvm_write_guest_cached(v->kvm, &vcpu->pv_time,

				&vcpu->hv_clock,

				sizeof(vcpu->hv_clock));



	kunmap_atomic(shared_kaddr);



	mark_page_dirty(v->kvm, vcpu->time >> PAGE_SHIFT);

	return 0;

}
@@ -1837,10 +1833,7 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data) 


static void kvmclock_reset(struct kvm_vcpu *vcpu)

{

	if (vcpu->arch.time_page) {

		kvm_release_page_dirty(vcpu->arch.time_page);

		vcpu->arch.time_page = NULL;

	}

	vcpu->arch.pv_time_enabled = false;

}



static void accumulate_steal_time(struct kvm_vcpu *vcpu)
@@ -1947,6 +1940,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) 
		break;

	case MSR_KVM_SYSTEM_TIME_NEW:

	case MSR_KVM_SYSTEM_TIME: {

		u64 gpa_offset;

		kvmclock_reset(vcpu);



		vcpu->arch.time = data;
@@ -1956,19 +1950,17 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) 
		if (!(data & 1))

			break;



		/* ...but clean it before doing the actual write */

		vcpu->arch.time_offset = data & ~(PAGE_MASK | 1);

		gpa_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))

		if (gpa_offset & (sizeof(struct pvclock_vcpu_time_info) - 1))

			break;



		vcpu->arch.time_page =

				gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT);



		if (is_error_page(vcpu->arch.time_page))

			vcpu->arch.time_page = NULL;

		if (kvm_gfn_to_hva_cache_init(vcpu->kvm,

		     &vcpu->arch.pv_time, data & ~1ULL))

			vcpu->arch.pv_time_enabled = false;

		else

			vcpu->arch.pv_time_enabled = true;



		break;

	}
@@ -2972,7 +2964,7 @@ static int kvm_vcpu_ioctl_x86_set_xcrs(struct kvm_vcpu *vcpu, 
 */

static int kvm_set_guest_paused(struct kvm_vcpu *vcpu)

{

	if (!vcpu->arch.time_page)

	if (!vcpu->arch.pv_time_enabled)

		return -EINVAL;

	vcpu->arch.pvclock_set_guest_stopped_request = true;

	kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
@@ -6723,6 +6715,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) 
		goto fail_free_wbinvd_dirty_mask;



	vcpu->arch.ia32_tsc_adjust_msr = 0x0;

	vcpu->arch.pv_time_enabled = false;

	kvm_async_pf_hash_reset(vcpu);

	kvm_pmu_init(vcpu);

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