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Date: Thu, 30 Nov 2017 12:40:10 -0800
From: Kees Cook <keescook@...omium.org>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>,
Christoffer Dall <christoffer.dall@...aro.org>, Marc Zyngier <marc.zyngier@....com>,
Christian Borntraeger <borntraeger@...ibm.com>, Cornelia Huck <cohuck@...hat.com>,
James Hogan <james.hogan@...tec.com>, Paul Mackerras <paulus@...ba.org>,
kernel-hardening@...ts.openwall.com, Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH 2/2] kvm: x86: fix KVM_XEN_HVM_CONFIG ioctl
On Thu, Oct 26, 2017 at 6:45 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> This ioctl is obsolete (it was used by Xenner as far as I know) but
> still let's not break it gratuitously... Its handler is copying
> directly into struct kvm. Go through a bounce buffer instead, with
> the added benefit that we can actually do something useful with the
> flags argument---the previous code was exiting with -EINVAL but still
> doing the copy.
>
> This technically is a userspace ABI breakage, but since no one should be
> using the ioctl, it's a good occasion to see if someone actually
> complains.
>
> Cc: kernel-hardening@...ts.openwall.com
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
> arch/x86/kvm/x86.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 272320eb328c..f32fbfb833b3 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4187,13 +4187,14 @@ long kvm_arch_vm_ioctl(struct file *filp,
> mutex_unlock(&kvm->lock);
> break;
> case KVM_XEN_HVM_CONFIG: {
> + struct kvm_xen_hvm_config xhc;
> r = -EFAULT;
> - if (copy_from_user(&kvm->arch.xen_hvm_config, argp,
> - sizeof(struct kvm_xen_hvm_config)))
> + if (copy_from_user(&xhc, argp, sizeof(xhc)))
> goto out;
> r = -EINVAL;
> - if (kvm->arch.xen_hvm_config.flags)
> + if (xhc.flags)
> goto out;
> + memcpy(&kvm->arch.xen_hvm_config, &xhc, sizeof(xhc));
> r = 0;
> break;
> }
> --
> 2.14.2
>
Hi Paolo,
Since this didn't make it via my usercopy tree, do you want to take it
via KVM? It is a stand-alone fix, AIUI.
Thanks,
-Kees
--
Kees Cook
Pixel Security
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