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Date: Thu, 26 Oct 2017 16:13:42 +0200
From: Cornelia Huck <cohuck@...hat.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, Christoffer Dall
 <christoffer.dall@...aro.org>, Marc Zyngier <marc.zyngier@....com>,
 Christian Borntraeger <borntraeger@...ibm.com>, James Hogan
 <james.hogan@...tec.com>, Paul Mackerras <paulus@...ba.org>,
 kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org>,
 Christoffer Dall <cdall@...aro.org>, Radim Krčmář
 <rkrcmar@...hat.com>
Subject: Re: [PATCH 1/2] kvm: whitelist struct kvm_vcpu_arch

On Thu, 26 Oct 2017 15:45:46 +0200
Paolo Bonzini <pbonzini@...hat.com> wrote:

> On x86, ARM and s390, struct kvm_vcpu_arch has a usercopy region
> taht is read and written by the KVM_GET/SET_CPUID2 ioctls (x86)
> or KVM_GET/SET_ONE_REG (ARM/s390).  Without whitelisting the area,
> KVM is completely broken on those architectures with usercopy hardening
> enabled.
> 
> For now, allow writing to the entire struct on all architectures.
> The KVM tree will not refine this to an architecture-specific
> subset of struct kvm_vcpu_arch.
> 
> Cc: kernel-hardening@...ts.openwall.com
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Christian Borntraeger <borntraeger@...hat.com>
> Cc: Christoffer Dall <cdall@...aro.org>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  virt/kvm/kvm_main.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 4d81f6ded88e..b4809ccfdfa1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4005,8 +4005,12 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
>  	/* A kmem cache lets us meet the alignment requirements of fx_save. */
>  	if (!vcpu_align)
>  		vcpu_align = __alignof__(struct kvm_vcpu);
> -	kvm_vcpu_cache = kmem_cache_create("kvm_vcpu", vcpu_size, vcpu_align,
> -					   0, NULL);
> +	kvm_vcpu_cache =
> +		kmem_cache_create_usercopy("kvm_vcpu",
> +					   sizeof(struct kvm_vcpu), vcpu_align,
> +					   0, offsetof(struct kvm_vcpu, arch),
> +					   sizeof_field(struct kvm_vcpu, arch),
> +					   NULL);
>  	if (!kvm_vcpu_cache) {
>  		r = -ENOMEM;
>  		goto out_free_3;

Acked-by: Cornelia Huck <cohuck@...hat.com>

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