Re: [Xen-devel] [PATCH v12 05/11] x86/mm: add HYPERVISOR_memory_op to acquire guest resources

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.10.17 at 15:24, <paul.durrant@xxxxxxxxxx> wrote:
> @@ -535,6 +588,48 @@ int compat_memory_op(unsigned int cmd, 
> XEN_GUEST_HANDLE_PARAM(void) compat)
>                  rc = -EFAULT;
>              break;
>  
> +        case XENMEM_acquire_resource:
> +        {
> +            const xen_ulong_t *xen_frame_list =
> +                (xen_ulong_t *)(nat.mar + 1);
> +            compat_ulong_t *compat_frame_list =
> +                (compat_ulong_t *)(nat.mar + 1);
> +
> +            if ( cmp.mar.nr_frames == 0 )

Doesn't this need to be compat_handle_is_null(cmp.mar.frame_list), or
a combination of both?

> +            {
> +                DEFINE_XEN_GUEST_HANDLE(compat_mem_acquire_resource_t);
> +
> +                if ( __copy_field_to_guest(
> +                         guest_handle_cast(compat,
> +                                           compat_mem_acquire_resource_t),
> +                         &cmp.mar, nr_frames) )
> +                    return -EFAULT;
> +            }
> +            else
> +            {
> +                /*
> +                 * NOTE: the smaller compat array overwrites the native
> +                 *       array.
> +                 */

I think I had already asked for a respective BUILD_BUG_ON().

> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -965,6 +965,95 @@ static long xatp_permission_check(struct domain *d, 
> unsigned int space)
>      return xsm_add_to_physmap(XSM_TARGET, current->domain, d);
>  }
>  
> +static int acquire_resource(
> +    XEN_GUEST_HANDLE_PARAM(xen_mem_acquire_resource_t) arg)
> +{
> +    struct domain *d, *currd = current->domain;
> +    xen_mem_acquire_resource_t xmar;
> +    unsigned long mfn_list[2];
> +    int rc;
> +
> +    if ( copy_from_guest(&xmar, arg, 1) )
> +        return -EFAULT;
> +
> +    if ( xmar.pad != 0 )
> +        return -EINVAL;
> +
> +    if ( guest_handle_is_null(xmar.frame_list) )
> +    {
> +        /* Special case for querying implementation limit */
> +        if ( xmar.nr_frames == 0 )

Perhaps invert the condition to reduce ...

> +        {
> +            xmar.nr_frames = ARRAY_SIZE(mfn_list);
> +
> +            if ( __copy_field_to_guest(arg, &xmar, nr_frames) )
> +                return -EFAULT;
> +
> +            return 0;
> +        }

... overall indentation?

> +        return -EINVAL;
> +    }
> +
> +    if ( xmar.nr_frames == 0 )
> +        return -EINVAL;

Why? (Almost?) everywhere else zero counts are simply no-ops, which
result in success returns.

> +    if ( xmar.nr_frames > ARRAY_SIZE(mfn_list) )
> +        return -E2BIG;
> +
> +    d = rcu_lock_domain_by_any_id(xmar.domid);

This being a tools only interface, why "by_any_id" instead of
"remote_domain_by_id"? In particular ...

> +    if ( d == NULL )
> +        return -ESRCH;
> +
> +    rc = xsm_domain_resource_map(XSM_DM_PRIV, d);

... an unprivileged dm domain should probably not be permitted to
invoke this on itself.

> +    if ( rc )
> +        goto out;
> +
> +    switch ( xmar.type )
> +    {
> +    default:
> +        rc = -EOPNOTSUPP;
> +        break;
> +    }
> +
> +    if ( rc )
> +        goto out;
> +
> +    if ( !paging_mode_translate(currd) )
> +    {
> +        if ( copy_to_guest(xmar.frame_list, mfn_list, xmar.nr_frames) )
> +            rc = -EFAULT;
> +    }
> +    else
> +    {
> +        xen_pfn_t gfn_list[ARRAY_SIZE(mfn_list)];
> +        unsigned int i;
> +
> +        rc = -EFAULT;
> +        if ( copy_from_guest(gfn_list, xmar.frame_list, xmar.nr_frames) )
> +            goto out;
> +
> +        for ( i = 0; i < xmar.nr_frames; i++ )
> +        {
> +            rc = set_foreign_p2m_entry(currd, gfn_list[i],
> +                                       _mfn(mfn_list[i]));
> +            if ( rc )
> +            {
> +                /*
> +                 * Make sure rc is -EIO for any interation other than
> +                 * the first.

"iteration", but why is this important in the first place?

> --- a/xen/include/public/memory.h
> +++ b/xen/include/public/memory.h
> @@ -599,6 +599,47 @@ struct xen_reserved_device_memory_map {
>  typedef struct xen_reserved_device_memory_map 
> xen_reserved_device_memory_map_t;
>  DEFINE_XEN_GUEST_HANDLE(xen_reserved_device_memory_map_t);
>  
> +/*
> + * Get the pages for a particular guest resource, so that they can be
> + * mapped directly by a tools domain.
> + */
> +#define XENMEM_acquire_resource 28
> +struct xen_mem_acquire_resource {
> +    /* IN - the domain whose resource is to be mapped */
> +    domid_t domid;
> +    /* IN - the type of resource */
> +    uint16_t type;
> +    /*
> +     * IN - a type-specific resource identifier, which must be zero
> +     *      unless stated otherwise.
> +     */
> +    uint32_t id;
> +    /* IN/OUT - As an IN parameter number of frames of the resource
> +     *          to be mapped. However, if the specified value is 0 and
> +     *          frame_list is NULL then this field will be set to the
> +     *          maximum value supported by the implementation on return.
> +     */
> +    uint32_t nr_frames;
> +    uint32_t pad;
> +    /* IN - the index of the initial frame to be mapped. This parameter
> +     *      is ignored if nr_frames is 0.
> +     */
> +    uint64_aligned_t frame;
> +    /* IN/OUT - If the tools domain is PV then, upon return, frame_list
> +     *          will be populated with the MFNs of the resource.
> +     *          If the tools domain is HVM then it is expected that, on
> +     *          entry, frame_list will be populated with a list of GFNs
> +     *          that will be mapped to the MFNs of the resource.
> +     *          If -EIO is returned then the frame_list has only been
> +     *          partially mapped and it is up to the caller to unmap all
> +     *          the GFNs.
> +     *          This parameter may be NULL if nr_frames is 0.
> +     */
> +    XEN_GUEST_HANDLE(xen_ulong_t) frame_list;

This is still xen_ulong_t, which I can live with, but then you shouldn't
copy into / out of arrays of other types in acquire_resource() (the
more that this is common code, and iirc xen_ulong_t and
unsigned long aren't the same thing on ARM32).

Jan

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