ima: define a canonical binary_runtime_measurements list format

The IMA binary_runtime_measurements list is currently in platform native
format.

To allow restoring a measurement list carried across kexec with a
different endianness than the targeted kernel, this patch defines
little-endian as the canonical format.  For big endian systems wanting
to save/restore the measurement list from a system with a different
endianness, a new boot command line parameter named "ima_canonical_fmt"
is defined.

Considerations: use of the "ima_canonical_fmt" boot command line option
will break existing userspace applications on big endian systems
expecting the binary_runtime_measurements list to be in platform native
format.

Link: http://lkml.kernel.org/r/1480554346-29071-10-git-send-email-zohar@linux.vnet.ibm.com
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Acked-by: Dmitry Kasatkin <dmitry.kasatkin@gmail.com>
Cc: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andreas Steffen <andreas.steffen@strongswan.org>
Cc: Josh Sklar <sklar@linux.vnet.ibm.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Stewart Smith <stewart@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

security/integrity/ima/ima.h

@@ -122,6 +122,12 @@ void ima_load_kexec_buffer(void);
 static inline void ima_load_kexec_buffer(void) {}
 #endif /* CONFIG_HAVE_IMA_KEXEC */
 
+/*
+ * The default binary_runtime_measurements list format is defined as the
+ * platform native format.  The canonical format is defined as little-endian.
+ */
+extern bool ima_canonical_fmt;
+
 /* Internal IMA function definitions */
 int ima_init(void);
 int ima_fs_init(void);