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Date: Mon, 23 Oct 2017 16:15:32 +0200
From: Paolo Bonzini <>
To: Cornelia Huck <>, David Hildenbrand <>
Cc:,,, Kees Cook <>,
 Radim Krčmář <>,
 Christoffer Dall <>,
 Marc Zyngier <>,
 Christian Borntraeger <>,
 James Hogan <>, Paul Mackerras <>
Subject: Re: [PATCH 0/2] KVM: fixes for the kernel-hardening tree

On 23/10/2017 14:39, Cornelia Huck wrote:
> On Mon, 23 Oct 2017 11:52:51 +0200
> David Hildenbrand <> wrote:
>> On 21.10.2017 01:25, Paolo Bonzini wrote:
>>> Two KVM ioctls (KVM_GET/SET_CPUID2) directly access the cpuid_entries
>>> field of struct kvm_vcpu_arch.  Therefore, the new usercopy hardening
>>> work in linux-next, which forbids copies from and to slab objects
>>> unless they are from kmalloc or explicitly whitelisted, breaks KVM
>>> completely.
>>> This series fixes it by adding the two new usercopy arguments
>>> to kvm_init (more precisely to a new function kvm_init_usercopy,
>>> while kvm_init passes zeroes as a default).
>>> There's also another broken ioctl, KVM_XEN_HVM_CONFIG, but it is
>>> obsolete and not a big deal at all.
>>> I'm Ccing all submaintainers in case they have something similar
>>> going on in their kvm_arch and kvm_vcpu_arch structs.  KVM has a
>>> pretty complex userspace API, so thorough with linux-next is highly
>>> recommended.  
>> I assume on s390x, at least
>> kvm_arch_vcpu_ioctl_get_one_reg() and
>> kvm_arch_vcpu_ioctl_set_one_reg()
>> have to be fixed.
> At a glance, seems like it.
>> Christian, are you already looking into this?
> I'm afraid I'm also busy with travel preparation/travel, so I'd be glad
> for any takers.

Let's do a generic fix now, so that we don't need to rush the switch to
explicit whitelisting.


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