[Xen-devel] [PATCH v8 14/14] xen/common: do not implicitly permit access to mapped I/O memory

[Arianna Avanzini <avanzini.arianna@xxxxxxxxx>]

Currently, the XEN_DOMCTL_memory_mapping hypercall implicitly grants
to a domain access permission to the I/O memory areas mapped in its
guest address space. This conflicts with the presence of a specific
hypercall (XEN_DOMCTL_iomem_permission) used to grant such a permission
to a domain.
This commit separates the functions of the two hypercalls by having only
the latter be able to permit I/O memory access to a domain, and the former
just performing the mapping after a permissions check on both the granting
and the grantee domains.

Signed-off-by: Arianna Avanzini <avanzini.arianna@xxxxxxxxx>
Cc: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Cc: Paolo Valente <paolo.valente@xxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxxxxx>
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Eric Trudeau <etrudeau@xxxxxxxxxxxx>
Cc: Viktor Kleinik <viktor.kleinik@xxxxxxxxxxxxxxx>

---

    v8:
        - Drop iomem_permission-related changes.
        - Conservatively check both the granting and the grantee domains'
          permissions in the memory_mapping DOMCTL.
        - Remove tentative phrases from commit description.

    v7:
        - Let iomem_permission check if the calling domain is allowed to access
          memory ranges to be mapped to a domain. Remove such a check from the
          memory_mapping hypercall.

---
 xen/common/domctl.c | 36 ++++++++++--------------------------
 1 file changed, 10 insertions(+), 26 deletions(-)

diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 1b246d1..bf38242 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -839,7 +839,8 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
u_domctl)
             break;
 
         ret = -EPERM;
-        if ( !iomem_access_permitted(current->domain, mfn, mfn_end) )
+        if ( !iomem_access_permitted(current->domain, mfn, mfn_end) ||
+             !iomem_access_permitted(d, mfn, mfn_end) )
             break;
 
         ret = xsm_iomem_mapping(XSM_HOOK, d, mfn, mfn_end, add);
@@ -852,40 +853,23 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
u_domctl)
                    "memory_map:add: dom%d gfn=%lx mfn=%lx nr=%lx\n",
                    d->domain_id, gfn, mfn, nr_mfns);
 
-            ret = iomem_permit_access(d, mfn, mfn_end);
-            if ( !ret )
-            {
-                ret = map_mmio_regions(d, gfn, nr_mfns, _mfn(mfn));
-                if ( ret )
-                {
-                    printk(XENLOG_G_WARNING
-                           "memory_map:fail: dom%d gfn=%lx mfn=%lx ret:%ld\n",
-                           d->domain_id, gfn, mfn, ret);
-                    if ( iomem_deny_access(d, mfn, mfn_end) &&
-                         is_hardware_domain(current->domain) )
-                        printk(XENLOG_ERR
-                               "memory_map: failed to deny dom%d access to 
[%lx,%lx]\n",
-                               d->domain_id, mfn, mfn_end);
-                }
-            }
+            ret = map_mmio_regions(d, gfn, nr_mfns, _mfn(mfn));
+            if ( ret )
+                printk(XENLOG_G_WARNING
+                       "memory_map:fail: dom%d gfn=%lx mfn=%lx ret:%ld\n",
+                       d->domain_id, gfn, mfn, ret);
         }
         else
         {
-            int rc = 0;
-
             printk(XENLOG_G_INFO
                    "memory_map:remove: dom%d gfn=%lx mfn=%lx nr=%lx\n",
                    d->domain_id, gfn, mfn, nr_mfns);
 
-            rc = unmap_mmio_regions(d, gfn, nr_mfns, _mfn(mfn));
-            ret = iomem_deny_access(d, mfn, mfn_end);
-            if ( !ret )
-                ret = rc;
+            ret = unmap_mmio_regions(d, gfn, nr_mfns, _mfn(mfn));
             if ( ret && is_hardware_domain(current->domain) )
                 printk(XENLOG_ERR
-                       "memory_map: error %ld %s dom%d access to [%lx,%lx]\n",
-                       ret, rc ? "removing" : "denying", d->domain_id,
-                       mfn, mfn_end);
+                       "memory_map: error %ld removing dom%d access to 
[%lx,%lx]\n",
+                       ret, d->domain_id, mfn, mfn_end);
         }
         /* Do this unconditionally to cover errors on above failure paths. */
         memory_type_changed(d);
-- 
1.9.2


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