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KVM: x86: Convert MSR_KVM_SYSTEM_TIME to use gfn_to_hva_cache functions (CVE-2013-1797) 

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@google.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Andy Honig 2013-02-20 14:48:10 -08:00 committed by Greg Kroah-Hartman
parent ce7d866258
commit f6dfc740c1
2 changed files with 16 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/x86/include/asm/kvm_host.h
View File

@ -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;

39
arch/x86/kvm/x86.c
View File

@ -1114,7 +1114,6 @@ 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;
@ -1150,7 +1149,7 @@ 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;
/*
@ -1208,14 +1207,9 @@ 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;
}
@ -1504,10 +1498,7 @@ 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)
@ -1602,6 +1593,7 @@ 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;
@ -1611,21 +1603,17 @@ 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:
@ -6172,6 +6160,7 @@ 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);