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KVM: x86: Convert MSR_KVM_SYSTEM_TIME to use gfn_to_hva_cache functio…
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…ns (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: Andrew Honig <[email protected]>
Signed-off-by: Marcelo Tosatti <[email protected]>
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@matosatti
Andy Honig authored and matosatti committed Mar 19, 2013
1 parent c300aa6 commit 0b79459
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Showing 2 changed files with 22 additions and 29 deletions.
4 changes: 2 additions & 2 deletions arch/x86/include/asm/kvm_host.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down
47 changes: 20 additions & 27 deletions arch/x86/kvm/x86.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -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;

/*
Expand Down Expand Up @@ -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;
Expand All @@ -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,
sizeof(vcpu->hv_clock));

kunmap_atomic(shared_kaddr);

mark_page_dirty(v->kvm, vcpu->time >> PAGE_SHIFT);
kvm_write_guest_cached(v->kvm, &vcpu->pv_time,
&vcpu->hv_clock,
sizeof(vcpu->hv_clock));
return 0;
}

Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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;
Expand All @@ -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;
}
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);

Expand Down

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