linux-kernel - [32/45] KVM: x86: check for cr3 validity in ioctl_set

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Date:	Tue, 30 Mar 2010 15:48:52 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [32/45] KVM: x86: check for cr3 validity in ioctl_set_sregs

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Marcelo Tosatti <mtosatti@...hat.com>

commit 59839dfff5eabca01cc4e20b45797a60a80af8cb upstream.

Matt T. Yourst notes that kvm_arch_vcpu_ioctl_set_sregs lacks validity
checking for the new cr3 value:

"Userspace callers of KVM_SET_SREGS can pass a bogus value of cr3 to
the kernel. This will trigger a NULL pointer access in gfn_to_rmap()
when userspace next tries to call KVM_RUN on the affected VCPU and kvm
attempts to activate the new non-existent page table root.

This happens since kvm only validates that cr3 points to a valid guest
physical memory page when code *inside* the guest sets cr3. However, kvm
currently trusts the userspace caller (e.g. QEMU) on the host machine to
always supply a valid page table root, rather than properly validating
it along with the rest of the reloaded guest state."

http://sourceforge.net/tracker/?func=detail&atid=893831&aid=2687641&group_id=180599

Check for a valid cr3 address in kvm_arch_vcpu_ioctl_set_sregs, triple
fault in case of failure.

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
Signed-off-by: Avi Kivity <avi@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 arch/x86/kvm/x86.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3658,7 +3658,13 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct

 	vcpu->arch.cr2 = sregs->cr2;
 	mmu_reset_needed |= vcpu->arch.cr3 != sregs->cr3;
-	vcpu->arch.cr3 = sregs->cr3;
+
+	down_read(&vcpu->kvm->slots_lock);
+	if (gfn_to_memslot(vcpu->kvm, sregs->cr3 >> PAGE_SHIFT))
+		vcpu->arch.cr3 = sregs->cr3;
+	else
+		set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
+	up_read(&vcpu->kvm->slots_lock);

 	kvm_set_cr8(vcpu, sregs->cr8);

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