Re: [Xen-devel] [PATCH] x86/hvm: Allow the guest to permit the use of userspace hypercalls

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.01.16 at 14:59, <andrew.cooper3@xxxxxxxxxx> wrote:
> Currently, hypercalls issued from HVM userspace will unconditionally fail
> with -EPERM.
> 
> This is inflexible, and a guest may wish to allow userspace to make
> hypercalls.

I thought previous discussion had made clear that routing these
through ioctls or alike is the right approach, and hence the patch
isn't needed. The more that an all-or-nothing approach seems
pretty bold.

> @@ -6839,6 +6840,28 @@ long do_hvm_op(unsigned long op, 
> XEN_GUEST_HANDLE_PARAM(void) arg)
>          rc = do_altp2m_op(arg);
>          break;
>  
> +    case HVMOP_set_hypercall_dpl:
> +    {
> +        xen_hvm_hypercall_dpl_t a;
> +        struct domain *d;
> +
> +        if ( copy_from_guest(&a, arg, 1 ) )
> +            return -EFAULT;
> +
> +        rc = rcu_lock_remote_domain_by_id(a.domid, &d);
> +        if ( rc != 0 )
> +            return rc;
> +
> +        if ( current->domain != d )
> +            return -EPERM;
> +
> +        if ( !is_hvm_domain(d) || a.dpl > 3 )
> +            return -EINVAL;

-EDOM perhaps for the right side?

> diff --git a/xen/include/asm-x86/hvm/domain.h 
> b/xen/include/asm-x86/hvm/domain.h
> index a8cc2ad..006a142 100644
> --- a/xen/include/asm-x86/hvm/domain.h
> +++ b/xen/include/asm-x86/hvm/domain.h
> @@ -137,6 +137,8 @@ struct hvm_domain {
>      bool_t                 qemu_mapcache_invalidate;
>      bool_t                 is_s3_suspended;
>  
> +    uint32_t               hypercall_dpl;

uint8_t ?

Jan


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