[Xen-devel] [PATCH v3 2/2] xsm: hide detailed Xen version from unprivileged guests

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

Hide the following information that can help identify the running Xen
binary version: XENVER_extraversion, XENVER_compile_info, XENVER_changeset.
This makes harder for malicious guests to fingerprint Xen to identify
exploitable systems.

Add explicit cases for XENVER_commandline and XENVER_build_id as well
for better code readability.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
v2 --> v3:
- Remove hvmloader filtering
- Add ASSERT_UNREACHABLE

v1 --> v2:
- Added xsm_filter_denied() to hvmloader instead of modifying xen_deny()
- Made behaviour the same for both Release and Debug builds
- XENVER_capabilities is no longer hided

CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Julien Grall <julien@xxxxxxx>
CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
CC: Doug Goldstein <cardoe@xxxxxxxxxx>
---
 xen/include/xsm/dummy.h | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index b8e185e6fa..c00186d7b6 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -750,16 +750,23 @@ static XSM_INLINE int xsm_xen_version (XSM_DEFAULT_ARG 
uint32_t op)
     case XENVER_get_features:
         /* These sub-ops ignore the permission checks and return data. */
         return 0;
-    case XENVER_extraversion:
-    case XENVER_compile_info:
+
     case XENVER_capabilities:
-    case XENVER_changeset:
     case XENVER_pagesize:
     case XENVER_guest_handle:
         /* These MUST always be accessible to any guest by default. */
         return xsm_default_action(XSM_HOOK, current->domain, NULL);
-    default:
+
+    case XENVER_extraversion:
+    case XENVER_compile_info:
+    case XENVER_changeset:
+    case XENVER_commandline:
+    case XENVER_build_id:
         return xsm_default_action(XSM_PRIV, current->domain, NULL);
+
+    default:
+        ASSERT_UNREACHABLE();
+        return -EPERM;
     }
 }
 
-- 
2.17.1


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