On Wed, Apr 20, 2016 at 07:02:10PM +0200, Radim Krčmář wrote:
> 2016-04-20 17:44+0200, Greg Kurz:
> > Commit 338c7dbadd26 ("KVM: Improve create VCPU parameter (CVE-2013-4587)")
> > introduced a check to prevent potential kernel memory corruption in case
> > the vcpu id is too great.
> >
> > Unfortunately this check assumes vcpu ids grow in sequence with a common
> > difference of 1, which is wrong: archs are free to use vcpu id as they fit.
> > For example, QEMU originated vcpu ids for PowerPC cpus running in boot3s_hv
> > mode, can grow with a common difference of 2, 4 or 8: if KVM_MAX_VCPUS is
> > 1024, guests may be limited down to 128 vcpus on POWER8.
> >
> > This means the check does not belong here and should be moved to some arch
> > specific function: kvm_arch_vcpu_create() looks like a good candidate.
> >
> > ARM and s390 already have such a check.
> >
> > I could not spot any path in the PowerPC or common KVM code where a vcpu
> > id is used as described in the above commit: I believe PowerPC can live
> > without this check.
> >
> > In the end, this patch simply moves the check to MIPS and x86.
> >
> > Signed-off-by: Greg Kurz <gkurz@xxxxxxxxxxxxxxxxxx>
> > ---
> > v3: use ERR_PTR()
> >
> > arch/mips/kvm/mips.c | 7 ++++++-
> > arch/x86/kvm/x86.c | 3 +++
> > virt/kvm/kvm_main.c | 3 ---
> > 3 files changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> > index 70ef1a43c114..0278ea146db5 100644
> > --- a/arch/mips/kvm/mips.c
> > +++ b/arch/mips/kvm/mips.c
> > @@ -248,9 +248,14 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
> > int err, size, offset;
> > void *gebase;
> > int i;
> > + struct kvm_vcpu *vcpu;
> >
> > - struct kvm_vcpu *vcpu = kzalloc(sizeof(struct kvm_vcpu), GFP_KERNEL);
> > + if (id >= KVM_MAX_VCPUS) {
> > + err = -EINVAL;
> > + goto out;
>
> 'vcpu' looks undefined at this point, so kfree in 'out:' may bug.
Thats out_free_cpu I think?
Cheers
James
> Just 'return ERR_PTR(-EINVAL)'?
>
> > + }
> >
> > + vcpu = kzalloc(sizeof(struct kvm_vcpu), GFP_KERNEL);
> > if (!vcpu) {
> > err = -ENOMEM;
> > goto out;
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