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.
Just 'return ERR_PTR(-EINVAL)'?
> + }
>
> + vcpu = kzalloc(sizeof(struct kvm_vcpu), GFP_KERNEL);
> if (!vcpu) {
> err = -ENOMEM;
> goto out;
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