KEYS: Reserve an extra certificate symbol for inserting without recompiling

Place a system_extra_cert buffer of configurable size, right after the
system_certificate_list, so that inserted keys can be readily processed by
the existing mechanism. Added script takes a key file and a kernel image
and inserts its contents to the reserved area. The
system_certificate_list_size is also adjusted accordingly.

Call the script as:

    scripts/insert-sys-cert -b <vmlinux> -c <certfile>

If vmlinux has no symbol table, supply System.map file with -s flag.
Subsequent runs replace the previously inserted key, instead of appending
the new one.

Signed-off-by: Mehmet Kayaalp <mkayaalp@linux.vnet.ibm.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

certs/Kconfig

@@ -39,4 +39,20 @@ config SYSTEM_TRUSTED_KEYS
 	  form of DER-encoded *.x509 files in the top-level build directory,
 	  those are no longer used. You will need to set this option instead.
 
+config SYSTEM_EXTRA_CERTIFICATE
+	bool "Reserve area for inserting a certificate without recompiling"
+	depends on SYSTEM_TRUSTED_KEYRING
+	help
+	  If set, space for an extra certificate will be reserved in the kernel
+	  image. This allows introducing a trusted certificate to the default
+	  system keyring without recompiling the kernel.
+
+config SYSTEM_EXTRA_CERTIFICATE_SIZE
+	int "Number of bytes to reserve for the extra certificate"
+	depends on SYSTEM_EXTRA_CERTIFICATE
+	default 4096
+	help
+	  This is the number of bytes reserved in the kernel image for a
+	  certificate to be inserted.
+
 endmenu