tools/libxl: env variable to signal whether disk/nic backend is trusted

Introduce support in libxl for fetching the default backend trusted
option for disk and nic devices.

Users can set LIBXL_{DISK,NIC}_BACKEND_UNTRUSTED environment variable
to notify libxl of whether the backends for disk and nic devices
should be trusted.  Such information is passed into the frontend so it
can take the appropriate measures.

This is part of XSA-403.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>

diff --git a/docs/man/xl.1.pod.in b/docs/man/xl.1.pod.in
index e2176bd696cbb6246015cbc2832fb85b4ac8986b..45e1430aeb7446999ea25cde8b99c1c3fb980c99 100644 (file)
--- a/docs/man/xl.1.pod.in
+++ b/docs/man/xl.1.pod.in
@@ -1946,6 +1946,24 @@ shows the decimal value. For non-linear mode, it shows hexadecimal value.
 
 =back
 
+=head1 ENVIRONMENT
+
+=over 4
+
+=item B<LIBXL_DISK_BACKEND_UNTRUSTED>
+
+Set this environment variable to "1" to suggest to the guest that the disk
+backend shouldn't be trusted. If the variable is absent or set to "0", the
+backend will be trusted.
+
+=item B<LIBXL_NIC_BACKEND_UNTRUSTED>
+
+Set this environment variable to "1" to suggest to the guest that the network
+backend shouldn't be trusted. If the variable is absent or set to "0", the
+backend will be trusted.
+
+=back
+
 =head1 IGNORED FOR COMPATIBILITY WITH XM
 
 xl is mostly command-line compatible with the old xm utility used with

diff --git a/tools/libs/light/libxl_disk.c b/tools/libs/light/libxl_disk.c
index 93936d0dd0f8ac9d284661bf863c2250b4a8f2d3..67d1cc18578fc738072265e15cc2c615d4892206 100644 (file)
--- a/tools/libs/light/libxl_disk.c
+++ b/tools/libs/light/libxl_disk.c
@@ -246,6 +246,7 @@ static void device_disk_add(libxl__egc *egc, uint32_t domid,
     libxl_domain_config d_config;
     libxl_device_disk disk_saved;
     libxl__flock *lock = NULL;
+    const char *envvar;
 
     libxl_domain_config_init(&d_config);
     libxl_device_disk_init(&disk_saved);
@@ -395,6 +396,10 @@ static void device_disk_add(libxl__egc *egc, uint32_t domid,
         flexarray_append(front, GCSPRINTF("%d", device->devid));
         flexarray_append(front, "device-type");
         flexarray_append(front, disk->is_cdrom ? "cdrom" : "disk");
+        flexarray_append(front, "trusted");
+        envvar = getenv("LIBXL_DISK_BACKEND_UNTRUSTED");
+        /* Set "trusted=1" if envvar missing or is "0". */
+        flexarray_append(front, !envvar || !strcmp("0", envvar) ? "1" : "0");
 
         /*
          * Old PV kernel disk frontends before 2.6.26 rely on tool stack to

diff --git a/tools/libs/light/libxl_nic.c b/tools/libs/light/libxl_nic.c
index 0b9e70c9d13da0c8f0c7974b441ed9f4d659b2a5..f87890d1d65f3cb004b57de1602748840e9a3998 100644 (file)
--- a/tools/libs/light/libxl_nic.c
+++ b/tools/libs/light/libxl_nic.c
@@ -132,6 +132,8 @@ static int libxl__set_xenstore_nic(libxl__gc *gc, uint32_t domid,
                                    flexarray_t *back, flexarray_t *front,
                                    flexarray_t *ro_front)
 {
+    const char *envvar;
+
     flexarray_grow(back, 2);
 
     if (nic->script)
@@ -255,6 +257,11 @@ static int libxl__set_xenstore_nic(libxl__gc *gc, uint32_t domid,
     flexarray_append(back, "hotplug-status");
     flexarray_append(back, "");
 
+    flexarray_append(front, "trusted");
+    envvar = getenv("LIBXL_NIC_BACKEND_UNTRUSTED");
+    /* Set "trusted=1" if envvar missing or is "0". */
+    flexarray_append(front, !envvar || !strcmp("0", envvar) ? "1" : "0");
+
     return 0;
 }