[068/126] KVM: x86: Convert MSR_KVM_SYSTEM_TIME to use gfn_to_hva_cache functions (CVE-2013-1797)

Steven Rostedt
2013-05-07T04:30:49Z

[-- Attachment #1: 0068-KVM-x86-Convert-MSR_KVM_SYSTEM_TIME-to-use-gfn_to_hv.patch --]
[-- Type: text/plain, Size: 4708 bytes --]

3.6.11.3 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Andy Honig <ahonig@google.com>

[ Upstream commit 0b79459b482e85cb7426aa7da683a9f2c97aeae1 ]

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 <ahonig@google.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
arch/x86/include/asm/kvm_host.h | 4 ++--
arch/x86/kvm/x86.c | 41 ++++++++++++++-------------------------
2 files changed, 17 insertions(+), 28 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 09155d6..69c9a92 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -418,8 +418,8 @@ 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;

struct {
u64 msr_val;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 142e18a..2bf95c0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1136,7 +1136,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
{
unsigned long flags;
struct kvm_vcpu_arch *vcpu = &v->arch;
- void *shared_kaddr;
unsigned long this_tsc_khz;
s64 kernel_ns, max_kernel_ns;
u64 tsc_timestamp;
@@ -1172,7 +1171,7 @@ 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;

/*
@@ -1230,14 +1229,9 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
*/
vcpu->hv_clock.version += 2;

- shared_kaddr = kmap_atomic(vcpu->time_page);
-
- 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;
}

@@ -1526,10 +1520,7 @@ 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)
@@ -1624,6 +1615,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
break;
case MSR_KVM_SYSTEM_TIME_NEW:
case MSR_KVM_SYSTEM_TIME: {
+ u64 gpa_offset;
kvmclock_reset(vcpu);

vcpu->arch.time = data;
@@ -1633,21 +1625,17 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
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)) {
- kvm_release_page_clean(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;
}
case MSR_KVM_ASYNC_PF_EN:
@@ -2641,7 +2629,7 @@ static int kvm_vcpu_ioctl_x86_set_xcrs(struct kvm_vcpu *vcpu,
static int kvm_set_guest_paused(struct kvm_vcpu *vcpu)
{
struct pvclock_vcpu_time_info *src = &vcpu->arch.hv_clock;
- if (!vcpu->arch.time_page)
+ if (!vcpu->arch.pv_time_enabled)
return -EINVAL;
src->flags |= PVCLOCK_GUEST_STOPPED;
mark_page_dirty(vcpu->kvm, vcpu->arch.time >> PAGE_SHIFT);
@@ -6237,6 +6225,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
if (!zalloc_cpumask_var(&vcpu->arch.wbinvd_dirty_mask, GFP_KERNEL))
goto fail_free_mce_banks;

+ vcpu->arch.pv_time_enabled = false;
kvm_async_pf_hash_reset(vcpu);
kvm_pmu_init(vcpu);

--
1.7.10.4