modsign: Allow external signing key to be specified

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 26 insertions, 5 deletions

diff --git a/Documentation/module-signing.txt b/Documentation/module-signing.txt
index faaa6ea002f7..84597c7ea175 100644
--- a/Documentation/module-signing.txt
+++ b/Documentation/module-signing.txt
@@ -88,6 +88,22 @@ This has a number of options available:
      than being a module) so that modules signed with that algorithm can have
      their signatures checked without causing a dependency loop.
 
+ (4) "File name or PKCS#11 URI of module signing key" (CONFIG_MODULE_SIG_KEY)
+
+     Setting this option to something other than its default of
+     "signing_key.priv" will disable the autogeneration of signing keys and
+     allow the kernel modules to be signed with a key of your choosing.
+     The string provided should identify a file containing a private key
+     in PEM form, or — on systems where the OpenSSL ENGINE_pkcs11 is
+     appropriately installed — a PKCS#11 URI as defined by RFC7512.
+
+     If the PEM file containing the private key is encrypted, or if the
+     PKCS#11 token requries a PIN, this can be provided at build time by
+     means of the KBUILD_SIGN_PIN variable.
+
+     The corresponding X.509 certificate in DER form should still be placed
+     in a file named signing_key.x509 in the top-level build directory.
+
 
 =======================
 GENERATING SIGNING KEYS
@@ -100,8 +116,9 @@ it can be deleted or stored securely.  The public key gets built into the
 kernel so that it can be used to check the signatures as the modules are
 loaded.
 
-Under normal conditions, the kernel build will automatically generate a new
-keypair using openssl if one does not exist in the files:
+Under normal conditions, when CONFIG_MODULE_SIG_KEY is unchanged from its
+default of "signing_key.priv", the kernel build will automatically generate
+a new keypair using openssl if one does not exist in the files:
 
 	signing_key.priv
 	signing_key.x509
@@ -135,8 +152,12 @@ kernel sources tree and the openssl command.  The following is an example to
 generate the public/private key files:
 
 	openssl req -new -nodes -utf8 -sha256 -days 36500 -batch -x509 \
-	   -config x509.genkey -outform DER -out signing_key.x509 \
-	   -keyout signing_key.priv
+	   -config x509.genkey -outform PEM -out kernel_key.pem \
+	   -keyout kernel_key.pem
+
+The full pathname for the resulting kernel_key.pem file can then be specified
+in the CONFIG_MODULE_SIG_KEY option, and the certificate and key therein will
+be used instead of an autogenerated keypair.
 
 
 =========================
@@ -181,7 +202,7 @@ To manually sign a module, use the scripts/sign-file tool available in
 the Linux kernel source tree.  The script requires 4 arguments:
 
 	1.  The hash algorithm (e.g., sha256)
-	2.  The private key filename
+	2.  The private key filename or PKCS#11 URI
 	3.  The public key filename
 	4.  The kernel module to be signed