[Xen-devel] [PATCH 2/2] xen: introduce xsrestrict

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Introduce a new command line option "xenopts", with one boolean
suboption "xsrestrict".  When xsrestrict=on is passed, QEMU will
restrict the xenstore connection calling xs_restrict. Also it won't
initialize the pv backends as they require higher privileges.

It requires a toolstack change to allow it to read/write to
/local/domain/0/device-model/$DOMID.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 include/hw/xen/xen.h |    2 ++
 qemu-options.hx      |   15 +++++++++++++++
 vl.c                 |    8 ++++++++
 xen-common-stub.c    |    2 ++
 xen-hvm.c            |   37 +++++++++++++++++++++++++++++--------
 5 files changed, 56 insertions(+), 8 deletions(-)

diff --git a/include/hw/xen/xen.h b/include/hw/xen/xen.h
index d118b56..e91bea9 100644
--- a/include/hw/xen/xen.h
+++ b/include/hw/xen/xen.h
@@ -54,4 +54,6 @@ void xen_register_framebuffer(struct MemoryRegion *mr);
 #  define HVM_MAX_VCPUS 32
 #endif
 
+extern QemuOptsList qemu_xen_opts;
+
 #endif /* QEMU_HW_XEN_H */
diff --git a/qemu-options.hx b/qemu-options.hx
index 64af16d..104f138 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3057,6 +3057,21 @@ the guest clock runs ahead of the host clock. Typically 
this happens
 when the shift value is high (how high depends on the host machine).
 ETEXI
 
+DEF("xenopts", HAS_ARG, QEMU_OPTION_xenopts, \
+    "-xenopts [xsrestrict=on|off]\n" \
+    "                Xen Specific Options\n", QEMU_ARCH_ALL)
+STEXI
+@item -xenopts [xsrestrict=on|off]
+@findex -xenopts
+Options for the Xen hypervisor:
+
+@option{xsrestrict=on} will cause QEMU to restrict its xenstore
+connection to the privilege level of the guest it is serving. This will
+cause QEMU not to initialize the Xen PV backends, as they require an higher
+privilege level.
+ETEXI
+
+
 DEF("watchdog", HAS_ARG, QEMU_OPTION_watchdog, \
     "-watchdog i6300esb|ib700\n" \
     "                enable virtual hardware watchdog [default=none]\n",
diff --git a/vl.c b/vl.c
index 81d80ae..acd4eea 100644
--- a/vl.c
+++ b/vl.c
@@ -2815,6 +2815,7 @@ int main(int argc, char **argv, char **envp)
     qemu_add_opts(&qemu_name_opts);
     qemu_add_opts(&qemu_numa_opts);
     qemu_add_opts(&qemu_icount_opts);
+    qemu_add_opts(&qemu_xen_opts);
 
     runstate_init();
 
@@ -3666,6 +3667,13 @@ int main(int argc, char **argv, char **envp)
                     exit(1);
                 }
                 break;
+            case QEMU_OPTION_xenopts:
+                opts = qemu_opts_parse(qemu_find_opts("xenopts"),
+                                              optarg, 0);
+                if (!opts) {
+                    exit(1);
+                }
+                break;
             case QEMU_OPTION_incoming:
                 incoming = optarg;
                 runstate_set(RUN_STATE_INMIGRATE);
diff --git a/xen-common-stub.c b/xen-common-stub.c
index 6fcfc96..579b4ce 100644
--- a/xen-common-stub.c
+++ b/xen-common-stub.c
@@ -8,6 +8,8 @@
 #include "qemu-common.h"
 #include "hw/xen/xen.h"
 
+QemuOptsList qemu_xen_opts = { };
+
 void xenstore_store_pv_console_info(int i, CharDriverState *chr)
 {
 }
diff --git a/xen-hvm.c b/xen-hvm.c
index 1ea567d..ac985b6 100644
--- a/xen-hvm.c
+++ b/xen-hvm.c
@@ -36,6 +36,19 @@
     do { } while (0)
 #endif
 
+QemuOptsList qemu_xen_opts = {
+    .name = "xenopts",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_xen_opts.head),
+    .merge_lists = true,
+    .desc = {
+        {
+            .name = "xsrestrict",
+            .type = QEMU_OPT_BOOL,
+        },
+        { /* end of list */ }
+    },
+};
+
 static MemoryRegion ram_memory, ram_640k, ram_lo, ram_hi;
 static MemoryRegion *framebuffer;
 static bool xen_in_migration;
@@ -1186,6 +1199,7 @@ int xen_hvm_init(ram_addr_t *below_4g_mem_size, 
ram_addr_t *above_4g_mem_size,
     xen_pfn_t bufioreq_pfn;
     evtchn_port_t bufioreq_evtchn;
     XenIOState *state;
+    QemuOpts *opts;
 
     state = g_malloc0(sizeof (XenIOState));
 
@@ -1304,16 +1318,23 @@ int xen_hvm_init(ram_addr_t *below_4g_mem_size, 
ram_addr_t *above_4g_mem_size,
     state->device_listener = xen_device_listener;
     device_listener_register(&state->device_listener);
 
-    /* Initialize backend core & drivers */
-    if (xen_be_init() != 0) {
-        fprintf(stderr, "%s: xen backend core setup failed\n", __FUNCTION__);
-        return -1;
-    }
-    xen_be_register("console", &xen_console_ops);
-    xen_be_register("vkbd", &xen_kbdmouse_ops);
-    xen_be_register("qdisk", &xen_blkdev_ops);
     xen_read_physmap(state);
 
+    opts = QTAILQ_FIRST(&qemu_xen_opts.head);
+    if (qemu_opt_get_bool(opts, "xsrestrict", false)) {
+        xs_restrict(state->xenstore, xen_domid);
+    } else {
+        /* Initialize backend core & drivers */
+        if (xen_be_init() != 0) {
+            fprintf(stderr, "%s: xen backend core setup failed\n", 
__FUNCTION__);
+            return -1;
+        }
+
+        xen_be_register("console", &xen_console_ops);
+        xen_be_register("vkbd", &xen_kbdmouse_ops);
+        xen_be_register("qdisk", &xen_blkdev_ops);
+    }
+
     return 0;
 }
 
-- 
1.7.10.4


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