3.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Andy Honig <ahonig@xxxxxxxxxx>
commit 0b79459b482e85cb7426aa7da683a9f2c97aeae1 upstream.
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@xxxxxxxxxx>
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 4 ++--
arch/x86/kvm/x86.c | 39 ++++++++++++++-------------------------
2 files changed, 16 insertions(+), 27 deletions(-)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -407,8 +407,8 @@ 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;
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1114,7 +1114,6 @@ static int kvm_guest_time_update(struct
{
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;
@@ -1150,7 +1149,7 @@ static int kvm_guest_time_update(struct
local_irq_restore(flags);
- if (!vcpu->time_page)
+ if (!vcpu->pv_time_enabled)
return 0;
/*
@@ -1208,14 +1207,9 @@ static int kvm_guest_time_update(struct
*/
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;
}
@@ -1504,10 +1498,7 @@ static int kvm_pv_enable_async_pf(struct
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)
@@ -1602,6 +1593,7 @@ int kvm_set_msr_common(struct kvm_vcpu *
break;
case MSR_KVM_SYSTEM_TIME_NEW:
case MSR_KVM_SYSTEM_TIME: {
+ u64 gpa_offset;
kvmclock_reset(vcpu);
vcpu->arch.time = data;
@@ -1611,21 +1603,17 @@ int kvm_set_msr_common(struct kvm_vcpu *
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:
@@ -6172,6 +6160,7 @@ int kvm_arch_vcpu_init(struct kvm_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);
--
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