[Xen-devel] [PATCH 2/2] xen/xsm: Add new SILO mode for XSM

[Xin Li <talons.lee@xxxxxxxxx>]

When SILO is enabled, there would be no page-sharing or event notifications
between unprivileged VMs (no grant tables or event channels).

Signed-off-by: Xin Li <xin.li@xxxxxxxxxx>

---
CC: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Ming Lu <ming.lu@xxxxxxxxxx>

v2
To further discuss:
1) is the new Kconfig option XSM_SILO necessary?
we can handle SILO similar as DUMMY, using exsting CONFIG_XSM.

2) explain "unmediated communication channel"

3) is it OK to use the indirect call dummy_xsm_ops.evtchn_unbound?

---
 docs/misc/xen-command-line.markdown |   5 +-
 xen/common/Kconfig                  |  12 ++++
 xen/include/xsm/xsm.h               |   6 ++
 xen/xsm/Makefile                    |   1 +
 xen/xsm/silo.c                      | 102 ++++++++++++++++++++++++++++
 xen/xsm/xsm_core.c                  |   9 +++
 6 files changed, 134 insertions(+), 1 deletion(-)
 create mode 100644 xen/xsm/silo.c

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index 7ca34aa273..6bbd67b436 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -866,7 +866,7 @@ Note that specifying zero as domU value means zero, while 
for dom0 it means
 to use the default.
 
 ### xsm
-> `= dummy | flask`
+> `= dummy | flask | silo`
 
 > Default: `dummy`
 
@@ -877,6 +877,9 @@ the hypervisor was compiled with XSM support.
   it's also used when XSM is compiled out.
 * `flask`: this is the policy based access control.  To choose this, the
   separated option in kconfig must also be enabled.
+* `silo`: this will deny any unmediated communication channels between
+  unprivileged VMs.  To choose this, the separated option in kconfig must also
+  be enabled.
 
 ### flask
 > `= permissive | enforcing | late | disabled`
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 068c3206a1..1f36dfcc5f 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -143,6 +143,18 @@ config XSM_FLASK_POLICY
 
          If unsure, say Y.
 
+config XSM_SILO
+       def_bool y
+       prompt "SILO support"
+       depends on XSM
+       ---help---
+         Enables SILO as the access control mechanism used by the XSM 
framework.
+         This is not the default module, add boot parameter xsm=silo to choose
+         it. This will deny any unmediated communication channels (grant tables
+         and event channels) between unprivileged VMs.
+
+         If unsure, say Y.
+
 config LATE_HWDOM
        bool "Dedicated hardware domain"
        default n
diff --git a/xen/include/xsm/xsm.h b/xen/include/xsm/xsm.h
index 70e7a6849f..11518e5bd6 100644
--- a/xen/include/xsm/xsm.h
+++ b/xen/include/xsm/xsm.h
@@ -733,6 +733,12 @@ extern const unsigned char xsm_init_flask_policy[];
 extern const unsigned int xsm_init_flask_policy_size;
 #endif
 
+#ifdef CONFIG_XSM_SILO
+extern void silo_init(void);
+#else
+static inline void silo_init(void) {}
+#endif
+
 #else /* CONFIG_XSM */
 
 #include <xsm/dummy.h>
diff --git a/xen/xsm/Makefile b/xen/xsm/Makefile
index 8bb4a24f09..e4d581e065 100644
--- a/xen/xsm/Makefile
+++ b/xen/xsm/Makefile
@@ -1,5 +1,6 @@
 obj-y += xsm_core.o
 obj-$(CONFIG_XSM) += xsm_policy.o
 obj-$(CONFIG_XSM) += dummy.o
+obj-$(CONFIG_XSM_SILO) += silo.o
 
 subdir-$(CONFIG_XSM_FLASK) += flask
diff --git a/xen/xsm/silo.c b/xen/xsm/silo.c
new file mode 100644
index 0000000000..d4416f3a95
--- /dev/null
+++ b/xen/xsm/silo.c
@@ -0,0 +1,102 @@
+/******************************************************************************
+ * xsm/silo.c
+ *
+ * SILO module for XSM(Xen Security Modules)
+ *
+ * Copyright (c) 2018 Citrix Systems Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <xen/sched.h>
+#include <xsm/xsm.h>
+
+struct xsm_operations silo_xsm_ops;
+
+/*
+ * Check if inter-domain communication is allowed.
+ * Return true when pass check.
+ */
+static bool silo_mode_dom_check(struct domain *ldom, struct domain *rdom)
+{
+    struct domain *cur_dom = current->domain;
+
+    return (is_control_domain(cur_dom) || is_control_domain(ldom) ||
+            is_control_domain(rdom) || ldom == rdom);
+}
+
+static int silo_evtchn_unbound(struct domain *d1, struct evtchn *chn,
+                               domid_t id2)
+{
+    int rc = -EPERM;
+    struct domain *d2 = rcu_lock_domain_by_id(id2);
+    if ( d2 != NULL && silo_mode_dom_check(d1, d2) )
+        rc = dummy_xsm_ops.evtchn_unbound(d1, chn, id2);
+    rcu_unlock_domain(d2);
+    return rc;
+}
+
+static int silo_evtchn_interdomain(struct domain *d1, struct evtchn *chan1,
+                                   struct domain *d2, struct evtchn *chan2)
+{
+    if ( silo_mode_dom_check(d1, d2) )
+        return dummy_xsm_ops.evtchn_interdomain(d1, chan1, d2, chan2);
+    return -EPERM;
+}
+
+static int silo_grant_mapref(struct domain *d1, struct domain *d2,
+                             uint32_t flags)
+{
+    if ( silo_mode_dom_check(d1, d2) )
+        return dummy_xsm_ops.grant_mapref(d1, d2, flags);
+    return -EPERM;
+}
+
+static int silo_grant_transfer(struct domain *d1, struct domain *d2)
+{
+    if ( silo_mode_dom_check(d1, d2) )
+        return dummy_xsm_ops.grant_transfer(d1, d2);
+    return -EPERM;
+}
+
+static int silo_grant_copy(struct domain *d1, struct domain *d2)
+{
+    if ( silo_mode_dom_check(d1, d2) )
+        return dummy_xsm_ops.grant_copy(d1, d2);
+    return -EPERM;
+}
+
+void __init silo_init(void)
+{
+    printk("Initialising XSM SILO mode\n");
+
+    silo_xsm_ops = dummy_xsm_ops;
+
+    silo_xsm_ops.evtchn_unbound = silo_evtchn_unbound;
+    silo_xsm_ops.evtchn_interdomain = silo_evtchn_interdomain;
+    silo_xsm_ops.grant_mapref = silo_grant_mapref;
+    silo_xsm_ops.grant_transfer = silo_grant_transfer;
+    silo_xsm_ops.grant_copy = silo_grant_copy;
+
+    xsm_ops = &silo_xsm_ops;
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/xsm/xsm_core.c b/xen/xsm/xsm_core.c
index d4668edad7..89d5fd3b2e 100644
--- a/xen/xsm/xsm_core.c
+++ b/xen/xsm/xsm_core.c
@@ -34,6 +34,7 @@ struct xsm_operations *xsm_ops;
 enum xsm_bootparam {
     XSM_BOOTPARAM_DUMMY,
     XSM_BOOTPARAM_FLASK,
+    XSM_BOOTPARAM_SILO,
 };
 
 static enum xsm_bootparam __initdata xsm_bootparam = XSM_BOOTPARAM_DUMMY;
@@ -46,6 +47,10 @@ static int __init parse_xsm_param(const char *s)
 #ifdef CONFIG_XSM_FLASK
     else if ( !strcmp(s, "flask") )
         xsm_bootparam = XSM_BOOTPARAM_FLASK;
+#endif
+#ifdef CONFIG_XSM_SILO
+    else if ( !strcmp(s, "silo") )
+        xsm_bootparam = XSM_BOOTPARAM_SILO;
 #endif
     else
         rc = -EINVAL;
@@ -91,6 +96,10 @@ static int __init xsm_core_init(const void *policy_buffer, 
size_t policy_size)
         flask_init(policy_buffer, policy_size);
         break;
 
+    case XSM_BOOTPARAM_SILO:
+        silo_init();
+        break;
+
     default:
         printk("XSM: Invalid value for xsm= boot parameter.\n");
         break;
-- 
2.18.0


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