Patchwork [3.5.y.z,extended,stable] Patch "KVM: x86: Convert MSR_KVM_SYSTEM_TIME to use gfn_to_hva_cache" has been added to staging queue

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Submitter Luis Henriques
Date April 11, 2013, 9:09 a.m.
Message ID <1365671382-12797-1-git-send-email-luis.henriques@canonical.com>
Download mbox | patch
Permalink /patch/235639/
State New
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Comments

Luis Henriques - April 11, 2013, 9:09 a.m.
This is a note to let you know that I have just added a patch titled

    KVM: x86: Convert MSR_KVM_SYSTEM_TIME to use gfn_to_hva_cache

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

From acec86b215d2889c467cd6e40a01c86bffff9df7 Mon Sep 17 00:00:00 2001
From: Andy Honig <ahonig@google.com>
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)

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>
[ luis: backported to 3.5:
  - Adjust context
  - Removed references to PVCLOCK_GUEST_STOPPED ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 arch/x86/include/asm/kvm_host.h |  4 ++--
 arch/x86/kvm/x86.c              | 40 +++++++++++++++-------------------------
 2 files changed, 17 insertions(+), 27 deletions(-)

--
1.8.1.2

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index db7c1f2..9a50912 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -410,8 +410,8 @@  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 ad5cf4b..5b4ac78 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1118,7 +1118,6 @@  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;
@@ -1154,7 +1153,7 @@  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;

 	/*
@@ -1212,14 +1211,9 @@  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;
 }

@@ -1508,10 +1502,7 @@  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)
@@ -1606,6 +1597,7 @@  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;
@@ -1615,21 +1607,18 @@  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 (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;

-		if (is_error_page(vcpu->arch.time_page)) {
-			kvm_release_page_clean(vcpu->arch.time_page);
-			vcpu->arch.time_page = NULL;
-		}
 		break;
 	}
 	case MSR_KVM_ASYNC_PF_EN:
@@ -2616,7 +2605,7 @@  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);
@@ -6216,6 +6205,7 @@  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);