xsm: add a default policy to .init.data

This adds a Kconfig option and support for including the XSM policy from
tools/flask/policy in the hypervisor so that the bootloader does not
need to provide a policy to get sane behavior from an XSM-enabled
hypervisor.  The policy provided by the bootloader, if present, will
override the built-in policy.

The XSM policy is not moved out of tools because that remains the
primary location for installing and configuring the policy.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

Config.mk

@@ -147,6 +147,12 @@ export XEN_HAS_BUILD_ID=y
 build_id_linker := --build-id=sha1
 endif
 
+ifndef XEN_HAS_CHECKPOLICY
+    CHECKPOLICY ?= checkpolicy
+    XEN_HAS_CHECKPOLICY := $(shell $(CHECKPOLICY) -h 2>&1 | grep -q xen && echo y || echo n)
+    export XEN_HAS_CHECKPOLICY
+endif
+
 # as-insn: Check whether assembler supports an instruction.
 # Usage: cflags-y += $(call as-insn "insn",option-yes,option-no)
 as-insn = $(if $(shell echo 'void _(void) { asm volatile ( $(2) ); }' \

INSTALL

@@ -269,10 +269,16 @@ Building the python tools may fail unless certain options are passed to
 setup.py. Config.mk contains additional info how to use this variable.
 PYTHON_PREFIX_ARG=
 
-The hypervisor may be build with XSM/Flask support, which can be changed
+The hypervisor may be built with XSM/Flask support, which can be changed
 by running:
 make -C xen menuconfig
-and enabling XSM/Flask in the 'Common Features' menu.
+and enabling XSM/Flask in the 'Common Features' menu.  A security policy
+is required to use XSM/Flask; if the SELinux policy compiler is
+available, the policy from tools can be included in the hypervisor.
+This option is enabled by default if XSM is enabled and the compiler
+(checkpolicy) is found.  The location of this executable can be set
+using the environment variable.
+CHECKPOLICY=
 
 Do a build for coverage.
 coverage=y

docs/misc/xen-command-line.markdown

@@ -712,13 +712,15 @@ enabled by running either:
   with untrusted guests.  If a policy is provided by the bootloader, it will be
   loaded; errors will be reported to the ring buffer but will not prevent
   booting.  The policy can be changed to enforcing mode using "xl setenforce".
-* `enforcing`: This requires a security policy to be provided by the bootloader
-  and will enter enforcing mode prior to the creation of domain 0.  If a valid
-  policy is not provided, the hypervisor will not continue booting.
-* `late`: This disables loading of the security policy from the bootloader.
-  FLASK will be enabled but will not enforce access controls until a policy is
-  loaded by a domain using "xl loadpolicy".  Once a policy is loaded, FLASK will
-  run in enforcing mode unless "xl setenforce" has changed that setting.
+* `enforcing`: This will cause the security server to enter enforcing mode prior
+  to the creation of domain 0.  If an valid policy is not provided by the
+  bootloader and no built-in policy is present, the hypervisor will not continue
+  booting.
+* `late`: This disables loading of the built-in security policy or the policy
+  provided by the bootloader.  FLASK will be enabled but will not enforce access
+  controls until a policy is loaded by a domain using "xl loadpolicy".  Once a
+  policy is loaded, FLASK will run in enforcing mode unless "xl setenforce" has
+  changed that setting.
 * `disabled`: This causes the XSM framework to revert to the dummy module.  The
   dummy module provides the same security policy as is used when compiling the
   hypervisor without support for XSM.  The xsm\_op hypercall can also be used to

docs/misc/xsm-flask.txt

@@ -141,21 +141,21 @@ only type enforcement is used and the user and role are set to system_u and
 system_r for all domains.
 
 The FLASK security framework is mostly configured using a security policy file.
-This policy file is not normally generated during the Xen build process because
-it relies on the SELinux compiler "checkpolicy"; run
+It relies on the SELinux compiler "checkpolicy"; if this is available, the
+policy will be compiled as part of the tools build.  If hypervisor support for a
+built-in policy is enabled ("Compile Xen with a built-in security policy"), the
+policy will be built during the hypervisor build.
 
-	make -C tools/flask/policy
+The policy is generated from definition files in tools/flask/policy.  Most
+changes to security policy will involve creating or modifying modules found in
+tools/flask/policy/modules/.  The modules.conf file there defines what modules
+are enabled and has short descriptions of each module.
 
-to compile the example policy included with Xen. The policy is generated from
-definition files under this directory. Most changes to security policy will
-involve creating or modifying modules found in tools/flask/policy/modules/.  The
-modules.conf file there defines what modules are enabled and has short
-descriptions of each module.
-
-The XSM policy file needs to be copied to /boot and loaded as a module by grub.
-The exact position of the module does not matter as long as it is after the Xen
-kernel; it is normally placed either just above the dom0 kernel or at the end.
-Once dom0 is running, the policy can be reloaded using "xl loadpolicy".
+If not using the built-in policy, the XSM policy file needs to be copied to
+/boot and loaded as a module by grub.  The exact position and filename of the
+module does not matter as long as it is after the Xen kernel; it is normally
+placed either just above the dom0 kernel or at the end.  Once dom0 is running,
+the policy can be reloaded using "xl loadpolicy".
 
 The example policy included with Xen demonstrates most of the features of FLASK
 that can be used without dom0 disaggregation. The main types for domUs are:

xen/common/Kconfig

@@ -46,6 +46,10 @@ config HAS_BUILD_ID
 	string
 	option env="XEN_HAS_BUILD_ID"
 
+config HAS_CHECKPOLICY
+	string
+	option env="XEN_HAS_CHECKPOLICY"
+
 # Enable/Disable kexec support
 config KEXEC
 	bool "kexec support"
@@ -143,6 +147,22 @@ config FLASK_AVC_STATS
 
 	  If unsure, say Y.
 
+config XSM_POLICY
+	bool "Compile Xen with a built-in security policy"
+	default y if HAS_CHECKPOLICY = "y"
+	depends on XSM
+	---help---
+	  This includes a default XSM policy in the hypervisor so that the
+	  bootloader does not need to load a policy to get sane behavior from an
+	  XSM-enabled hypervisor.  If this is disabled, a policy must be
+	  provided by the bootloader or by Domain 0.  Even if this is enabled, a
+	  policy provided by the bootloader will override it.
+
+	  This requires that the SELinux policy compiler (checkpolicy) be
+	  available when compiling the hypervisor.
+
+	  If unsure, say Y.
+
 # Enable schedulers
 menu "Schedulers"
 	visible if EXPERT = "y"

xen/include/xsm/xsm.h

@@ -761,6 +761,11 @@ static inline void flask_init(const void *policy_buffer, size_t policy_size)
 }
 #endif
 
+#ifdef CONFIG_XSM_POLICY
+extern const unsigned char xsm_init_policy[];
+extern const unsigned int xsm_init_policy_size;
+#endif
+
 #else /* CONFIG_XSM */
 
 #include <xsm/dummy.h>

xen/xsm/flask/.gitignore

@@ -0,0 +1 @@
+/policy.c

xen/xsm/flask/Makefile

@@ -27,6 +27,17 @@ $(FLASK_H_FILES): $(FLASK_H_DEPEND)
 $(AV_H_FILES): $(AV_H_DEPEND)
 	$(CONFIG_SHELL) policy/mkaccess_vector.sh $(AWK) $(AV_H_DEPEND)
 
+obj-$(CONFIG_XSM_POLICY) += policy.o
+
+POLICY_SRC := $(XEN_ROOT)/tools/flask/policy/xenpolicy-$(XEN_FULLVERSION)
+
+policy.bin: FORCE
+	$(MAKE) -C $(XEN_ROOT)/tools/flask/policy
+	cmp -s $(POLICY_SRC) $@ || cp $(POLICY_SRC) $@
+
+policy.c: policy.bin gen-policy.py
+	$(PYTHON) gen-policy.py < $< > $@
+
 .PHONY: clean
 clean::
-	rm -f $(ALL_H_FILES) *.o $(DEPS)
+	rm -f $(ALL_H_FILES) *.o $(DEPS) policy.c policy.bin

xen/xsm/flask/gen-policy.py

@@ -0,0 +1,23 @@
+#!/usr/bin/env python
+import sys
+
+policy_size = 0
+
+sys.stdout.write("""
+/* This file is autogenerated by gen_policy.py */
+#include <xen/init.h>
+#include <xsm/xsm.h>
+
+const unsigned char xsm_init_policy[] __initconst = {
+""")
+
+for char in sys.stdin.read():
+    sys.stdout.write(" 0x%02x," % ord(char))
+    policy_size = policy_size + 1
+    if policy_size % 13 == 0:
+        sys.stdout.write("\n")
+
+sys.stdout.write("""
+};
+const unsigned int __initconst xsm_init_policy_size = %d;
+""" % policy_size)

xen/xsm/xsm_core.c

@@ -38,6 +38,14 @@ static inline int verify(struct xsm_operations *ops)
 
 static int __init xsm_core_init(const void *policy_buffer, size_t policy_size)
 {
+#ifdef CONFIG_XSM_POLICY
+    if ( policy_size == 0 )
+    {
+        policy_buffer = xsm_init_policy;
+        policy_size = xsm_init_policy_size;
+    }
+#endif
+
     if ( verify(&dummy_xsm_ops) )
     {
         printk("%s could not verify "