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

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>
[bwh: Backported to 3.2:
 - Adjust context
 - We do not implement the PVCLOCK_GUEST_STOPPED flag]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b4973f4dab9832da8569ef17d264406ac5c668d7..cfb5a403a34d665369e2ef9fc9fe38d3924ebfdd 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -393,8 +393,8 @@ 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 50bac2e50ae3e66fda334fd3fd8bc59e524a565b..2dd2e4e19b7bcb78be86ea81b06107f6855e8059 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1105,7 +1105,6 @@ 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;
@@ -1141,7 +1140,7 @@ 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;
 
        /*
@@ -1199,14 +1198,9 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
         */
        vcpu->hv_clock.version += 2;
 
-       shared_kaddr = kmap_atomic(vcpu->time_page, KM_USER0);
-
-       memcpy(shared_kaddr + vcpu->time_offset, &vcpu->hv_clock,
-              sizeof(vcpu->hv_clock));
-
-       kunmap_atomic(shared_kaddr, KM_USER0);
-
-       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;
 }
 
@@ -1496,10 +1490,7 @@ 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)
@@ -1591,6 +1582,7 @@ 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;
@@ -1600,21 +1592,17 @@ 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:
@@ -6554,6 +6542,7 @@ 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);
 
        return 0;