Re: [PATCH] KVM: Forbid /dev/kvm being opened by a compat task when CONFIG_KVM_COMPAT=n

[Paolo Bonzini <pbonzini@redhat.com>]

On 14/11/19 14:22, Marc Zyngier wrote:
> 
> From 34bfc68752253c3da3e59072b137d1a4a85bc005 Mon Sep 17 00:00:00 2001
> From: Marc Zyngier <maz@kernel.org>
> Date: Thu, 14 Nov 2019 13:17:39 +0000
> Subject: [PATCH] KVM: Add a comment describing the /dev/kvm no_compat
> handling
> 
> Add a comment explaining the rational behind having both
> no_compat open and ioctl callbacks to fend off compat tasks.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  virt/kvm/kvm_main.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 1243e48dc717..722f2b1d4672 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -120,6 +120,13 @@ static long kvm_vcpu_compat_ioctl(struct file
> *file, unsigned int ioctl,
>                    unsigned long arg);
>  #define KVM_COMPAT(c)    .compat_ioctl    = (c)
>  #else
> +/*
> + * For architectures that don't implement a compat infrastructure,
> + * adopt a double line of defense:
> + * - Prevent a compat task from opening /dev/kvm
> + * - If the open has been done by a 64bit task, and the KVM fd
> + *   passed to a compat task, let the ioctls fail.
> + */
>  static long kvm_no_compat_ioctl(struct file *file, unsigned int ioctl,
>                  unsigned long arg) { return -EINVAL; }
> 
> -- 
> 2.20.1

Queued, thanks!

Paolo