xen/arm, libxl: Implement XEN_DOMCTL_shadow_op for Arm

This commit implements the `XEN_DOMCTL_shadow_op` support in Xen
for Arm. The p2m pages pool size for xl guests is supposed to be
determined by `XEN_DOMCTL_shadow_op`. Hence, this commit:

- Introduces a function `p2m_domctl` and implements the subops
`XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION` and
`XEN_DOMCTL_SHADOW_OP_GET_ALLOCATION` of `XEN_DOMCTL_shadow_op`.

- Adds the `XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION` support in libxl.

Therefore enabling the setting of shadow memory pool size
when creating a guest from xl and getting shadow memory pool size
from Xen.

Note that the `XEN_DOMCTL_shadow_op` added in this commit is only
a dummy op, and the functionality of setting/getting p2m memory pool
size for xl guests will be added in following commits.

This is part of CVE-2022-33747 / XSA-409.

Signed-off-by: Henry Wang <Henry.Wang@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

tools/libs/light/libxl_arm.c

@@ -209,6 +209,18 @@ int libxl__arch_domain_create(libxl__gc *gc,
                               libxl__domain_build_state *state,
                               uint32_t domid)
 {
+    libxl_ctx *ctx = libxl__gc_owner(gc);
+    unsigned int shadow_mb = DIV_ROUNDUP(d_config->b_info.shadow_memkb, 1024);
+
+    int r = xc_shadow_control(ctx->xch, domid,
+                              XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION,
+                              &shadow_mb, 0);
+    if (r) {
+        LOGED(ERROR, domid,
+              "Failed to set %u MiB shadow allocation", shadow_mb);
+        return ERROR_FAIL;
+    }
+
     return 0;
 }
 

xen/arch/arm/domctl.c

@@ -47,11 +47,43 @@ static int handle_vuart_init(struct domain *d,
     return rc;
 }
 
+static long p2m_domctl(struct domain *d, struct xen_domctl_shadow_op *sc,
+                       XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
+{
+    if ( unlikely(d == current->domain) )
+    {
+        printk(XENLOG_ERR "Tried to do a p2m domctl op on itself.\n");
+        return -EINVAL;
+    }
+
+    if ( unlikely(d->is_dying) )
+    {
+        printk(XENLOG_ERR "Tried to do a p2m domctl op on dying domain %u\n",
+               d->domain_id);
+        return -EINVAL;
+    }
+
+    switch ( sc->op )
+    {
+    case XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION:
+        return 0;
+    case XEN_DOMCTL_SHADOW_OP_GET_ALLOCATION:
+        return 0;
+    default:
+    {
+        printk(XENLOG_ERR "Bad p2m domctl op %u\n", sc->op);
+        return -EINVAL;
+    }
+    }
+}
+
 long arch_do_domctl(struct xen_domctl *domctl, struct domain *d,
                     XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
 {
     switch ( domctl->cmd )
     {
+    case XEN_DOMCTL_shadow_op:
+        return p2m_domctl(d, &domctl->u.shadow_op, u_domctl);
     case XEN_DOMCTL_cacheflush:
     {
         gfn_t s = _gfn(domctl->u.cacheflush.start_pfn);