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KVM: x86: check for cr3 validity in ioctl_set_sregs

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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.

Cc: stable@kernel.org
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Marcelo Tosatti 2009-04-16 08:30:44 -03:00 committed by Avi Kivity
parent c6b60c6921
commit 59839dfff5
1 changed files with 7 additions and 1 deletions
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8
arch/x86/kvm/x86.c
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@ -3993,7 +3993,13 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
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);