XENVER_build_id/libxc: Provide ld-embedded build-id

If the hypervisor was built with build-ids we can expose the
build-id value to the toolstack (if it is not built with
it will just return -ENODATA). This is a priviligied operation
so only the controlling stack is able to request this.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

tools/flask/policy/policy/modules/xen/xen.te

@@ -82,6 +82,7 @@ allow dom0_t xen_t:xen2 {
 allow dom0_t xen_t:version {
     xen_extraversion xen_compile_info xen_capabilities
     xen_changeset xen_pagesize xen_guest_handle xen_commandline
+    xen_build_id
 };
 
 allow dom0_t xen_t:mmu memorymap;

tools/libxc/xc_private.c

@@ -495,6 +495,13 @@ int xc_version(xc_interface *xch, int cmd, void *arg)
     case XENVER_commandline:
         sz = sizeof(xen_commandline_t);
         break;
+    case XENVER_build_id:
+        {
+            xen_build_id_t *build_id = (xen_build_id_t *)arg;
+            sz = sizeof(*build_id) + build_id->len;
+            HYPERCALL_BOUNCE_SET_DIR(arg, XC_HYPERCALL_BUFFER_BOUNCE_BOTH);
+            break;
+        }
     default:
         ERROR("xc_version: unknown command %d\n", cmd);
         return -EINVAL;

tools/libxc/xc_private.h

@@ -196,6 +196,17 @@ enum {
  */
 #define HYPERCALL_BOUNCE_SET_SIZE(_buf, _sz) do { (HYPERCALL_BUFFER(_buf))->sz = _sz; } while (0)
 
+/*
+ * Change the direction.
+ *
+ * Can only be used if the bounce_pre/bounce_post commands have
+ * not been used.
+ */
+#define HYPERCALL_BOUNCE_SET_DIR(_buf, _dir) do { if ((HYPERCALL_BUFFER(_buf))->hbuf)         \
+                                                        assert(1);                            \
+                                                   (HYPERCALL_BUFFER(_buf))->dir = _dir;      \
+                                                } while (0)
+
 /*
  * Initialise and free hypercall safe memory. Takes care of any required
  * copying.

xen/common/kernel.c

@@ -376,6 +376,42 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
             return -EFAULT;
         return 0;
     }
+
+    case XENVER_build_id:
+    {
+        xen_build_id_t build_id;
+        unsigned int sz;
+        int rc;
+        const void *p;
+
+        if ( deny )
+            return -EPERM;
+
+        /* Only return size. */
+        if ( !guest_handle_is_null(arg) )
+        {
+            if ( copy_from_guest(&build_id, arg, 1) )
+                return -EFAULT;
+
+            if ( build_id.len == 0 )
+                return -EINVAL;
+        }
+
+        rc = xen_build_id(&p, &sz);
+        if ( rc )
+            return rc;
+
+        if ( guest_handle_is_null(arg) )
+            return sz;
+
+        if ( sz > build_id.len )
+            return -ENOBUFS;
+
+        if ( copy_to_guest_offset(arg, offsetof(xen_build_id_t, buf), p, sz) )
+            return -EFAULT;
+
+        return sz;
+    }
     }
 
     return -ENOSYS;

xen/include/public/version.h

@@ -30,7 +30,8 @@
 
 #include "xen.h"
 
-/* NB. All ops return zero on success, except XENVER_{version,pagesize} */
+/* NB. All ops return zero on success, except XENVER_{version,pagesize}
+ * XENVER_{version,pagesize,build_id} */
 
 /* arg == NULL; returns major:minor (16:16). */
 #define XENVER_version      0
@@ -87,6 +88,21 @@ typedef struct xen_feature_info xen_feature_info_t;
 #define XENVER_commandline 9
 typedef char xen_commandline_t[1024];
 
+/*
+ * Return value is the number of bytes written, or XEN_Exx on error.
+ * Calling with empty parameter returns the size of build_id.
+ */
+#define XENVER_build_id 10
+struct xen_build_id {
+        uint32_t        len; /* IN: size of buf[]. */
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
+        unsigned char   buf[];
+#elif defined(__GNUC__)
+        unsigned char   buf[1]; /* OUT: Variable length buffer with build_id. */
+#endif
+};
+typedef struct xen_build_id xen_build_id_t;
+
 #endif /* __XEN_PUBLIC_VERSION_H__ */
 
 /*

xen/xsm/flask/hooks.c

@@ -1663,6 +1663,9 @@ static int flask_xen_version (uint32_t op)
     case XENVER_commandline:
         return avc_has_perm(dsid, SECINITSID_XEN, SECCLASS_VERSION,
                             VERSION__XEN_COMMANDLINE, NULL);
+    case XENVER_build_id:
+        return avc_has_perm(dsid, SECINITSID_XEN, SECCLASS_VERSION,
+                            VERSION__XEN_BUILD_ID, NULL);
     default:
         return -EPERM;
     }

xen/xsm/flask/policy/access_vectors

@@ -525,4 +525,6 @@ class version
     xen_guest_handle
 # Xen command line.
     xen_commandline
+# Xen build id
+    xen_build_id
 }