[CVE-2012-2121] precise/oneiric/natty KVM: unmap pages from the iommu when slots are removed

[Steve Conklin]

This is a backport from upstream. There are changes due to a change that
was made in parameters passed to a function, but it's straightforward
change.

>From 2739eaeac4a9bf777810b2837e528dbdbdb3d5cc Mon Sep 17 00:00:00 2001
From: Alex Williamson <alex.williamson at redhat.com>
Date: Wed, 11 Apr 2012 09:51:49 -0600
Subject: [PATCH] KVM: unmap pages from the iommu when slots are removed

CVE-2012-2121

BugLink: http://bugs.launchpad.net/bugs/987569

We've been adding new mappings, but not destroying old mappings.
This can lead to a page leak as pages are pinned using
get_user_pages, but only unpinned with put_page if they still
exist in the memslots list on vm shutdown.  A memslot that is
destroyed while an iommu domain is enabled for the guest will
therefore result in an elevated page reference count that is
never cleared.

Additionally, without this fix, the iommu is only programmed
with the first translation for a gpa.  This can result in
peer-to-peer errors if a mapping is destroyed and replaced by a
new mapping at the same gpa as the iommu will still be pointing
to the original, pinned memory address.

Signed-off-by: Alex Williamson <alex.williamson at redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti at redhat.com>

Backported with minor changes from upstream commit
32f6daad4651a748a58a3ab6da0611862175722f
Signed-off-by: Steve Conklin <sconklin at canonical.com>
---
 include/linux/kvm_host.h |    6 ++++++
 virt/kvm/iommu.c         |    8 ++++++--
 virt/kvm/kvm_main.c      |    5 +++--
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 7e8a29f..6136821 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -562,6 +562,7 @@ void kvm_free_irq_source_id(struct kvm *kvm, int
irq_source_id);

 #ifdef CONFIG_IOMMU_API
 int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot);
+void kvm_iommu_unmap_pages(struct kvm *kvm, struct kvm_memory_slot *slot);
 int kvm_iommu_map_guest(struct kvm *kvm);
 int kvm_iommu_unmap_guest(struct kvm *kvm);
 int kvm_assign_device(struct kvm *kvm,
@@ -575,6 +576,11 @@ static inline int kvm_iommu_map_pages(struct kvm *kvm,
 	return 0;
 }

+static inline void kvm_iommu_unmap_pages(struct kvm *kvm,
+					 struct kvm_memory_slot *slot)
+{
+}
+
 static inline int kvm_iommu_map_guest(struct kvm *kvm)
 {
 	return -ENODEV;
diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
index a195c07..981f55a 100644
--- a/virt/kvm/iommu.c
+++ b/virt/kvm/iommu.c
@@ -309,6 +309,11 @@ static void kvm_iommu_put_pages(struct kvm *kvm,
 	}
 }

+void kvm_iommu_unmap_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
+{
+	kvm_iommu_put_pages(kvm, slot->base_gfn, slot->npages);
+}
+
 static int kvm_iommu_unmap_memslots(struct kvm *kvm)
 {
 	int i, idx;
@@ -318,8 +323,7 @@ static int kvm_iommu_unmap_memslots(struct kvm *kvm)
 	slots = kvm_memslots(kvm);

 	for (i = 0; i < slots->nmemslots; i++) {
-		kvm_iommu_put_pages(kvm, slots->memslots[i].base_gfn,
-				    slots->memslots[i].npages);
+		kvm_iommu_unmap_pages(kvm, &slots->memslots[i]);
 	}
 	srcu_read_unlock(&kvm->srcu, idx);

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5007b7d..63e01de 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -802,12 +802,13 @@ skip_lpage:
 	if (r)
 		goto out_free;

-	/* map the pages in iommu page table */
+	/* map/unmap the pages in iommu page table */
 	if (npages) {
 		r = kvm_iommu_map_pages(kvm, &new);
 		if (r)
 			goto out_free;
-	}
+	} else
+		kvm_iommu_unmap_pages(kvm, &old);

 	r = -ENOMEM;
 	slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
-- 
1.7.9.5