From 0b79459b482e85cb7426aa7da683a9f2c97aeae1 Mon Sep 17 00:00:00 2001 From: Andy Honig Date: Wed, 20 Feb 2013 14:48:10 -0800 Subject: [PATCH] KVM: x86: Convert MSR_KVM_SYSTEM_TIME to use gfn_to_hva_cache functions (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 Signed-off-by: Marcelo Tosatti --- arch/x86/include/asm/kvm_host.h | 4 +-- arch/x86/kvm/x86.c | 47 ++++++++++++++------------------- 2 files changed, 22 insertions(+), 29 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 635a74d22409..4979778cc7fb 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -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; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 2ade60c25402..f19ac0aca60d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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; @@ -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; /* @@ -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; @@ -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; } @@ -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) @@ -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; @@ -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; } @@ -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); @@ -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); -- 2.20.1