[Xen-devel] [PATCH 19/23] arch/x86: check remote MMIO remap permissions

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

When a domain is mapping pages from a different pg_owner domain, the
iomem_access checks are currently only applied to the pg_owner domain,
potentially allowing the current domain to bypass its more restrictive
iomem_access policy using another domain that it has access to.

Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
---
 xen/arch/x86/mm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 5c6ea2d..c0c2bf3 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -754,6 +754,18 @@ get_page_from_l1e(
             return -EINVAL;
         }
 
+        if ( pg_owner != curr->domain &&
+             !iomem_access_permitted(curr->domain, mfn, mfn) )
+        {
+            if ( mfn != (PADDR_MASK >> PAGE_SHIFT) ) /* INVALID_MFN? */
+            {
+                MEM_LOG("Domain %u attempted to map I/O space %08lx in domain 
%u",
+                        curr->domain->domain_id, mfn, pg_owner->domain_id);
+                return -EPERM;
+            }
+            return -EINVAL;
+        }
+
         if ( !(l1f & _PAGE_RW) ||
              !rangeset_contains_singleton(mmio_ro_ranges, mfn) )
             return 0;
-- 
1.7.11.4


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