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Message-ID: <20150717161719.2578.22073.stgit@warthog.procyon.org.uk>
Date: Fri, 17 Jul 2015 17:17:19 +0100
From: David Howells <dhowells@...hat.com>
To: mcgrof@...il.com
Cc: mjg59@...f.ucam.org, keyrings@...ux-nfs.org,
gregkh@...uxfoundation.org, kyle@...nel.org,
linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
seth.forshee@...onical.com, linux-security-module@...r.kernel.org,
zohar@...ux.vnet.ibm.com, dwmw2@...radead.org
Subject: [PATCH 12/27] modsign: Allow external signing key to be specified
From: David Woodhouse <David.Woodhouse@...el.com>
Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>
Signed-off-by: David Howells <dhowells@...hat.com>
---
Documentation/module-signing.txt | 31 ++++++++++++++++++++++++++-----
Makefile | 2 +-
init/Kconfig | 14 ++++++++++++++
kernel/Makefile | 5 +++++
4 files changed, 46 insertions(+), 6 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
diff --git a/Makefile b/Makefile
index 95bb0ff83634..e1195798a00f 100644
--- a/Makefile
+++ b/Makefile
@@ -869,7 +869,7 @@ INITRD_COMPRESS-$(CONFIG_RD_LZ4) := lz4
# export INITRD_COMPRESS := $(INITRD_COMPRESS-y)
ifdef CONFIG_MODULE_SIG_ALL
-MODSECKEY = ./signing_key.priv
+MODSECKEY = $(CONFIG_MODULE_SIG_KEY)
MODPUBKEY = ./signing_key.x509
export MODPUBKEY
mod_sign_cmd = scripts/sign-file $(CONFIG_MODULE_SIG_HASH) $(MODSECKEY) $(MODPUBKEY)
diff --git a/init/Kconfig b/init/Kconfig
index 14b3d8422502..1b1148e9181b 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1948,6 +1948,20 @@ config MODULE_SIG_HASH
default "sha384" if MODULE_SIG_SHA384
default "sha512" if MODULE_SIG_SHA512
+config MODULE_SIG_KEY
+ string "File name or PKCS#11 URI of module signing key"
+ default "signing_key.priv"
+ depends on MODULE_SIG
+ help
+ Provide the file name of a private key in PKCS#8 PEM format, or
+ a PKCS#11 URI according to RFC7512. The corresponding X.509
+ certificate in DER form should be present in signing_key.x509
+ in the top-level build directory.
+
+ If this option is unchanged from its default "signing_key.priv",
+ then the kernel will automatically generate the private key and
+ certificate as described in Documentation/module-signing.txt
+
config MODULE_COMPRESS
bool "Compress modules on installation"
depends on MODULES
diff --git a/kernel/Makefile b/kernel/Makefile
index 43c4c920f30a..2c937ace292e 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -170,6 +170,10 @@ ifndef CONFIG_MODULE_SIG_HASH
$(error Could not determine digest type to use from kernel config)
endif
+# We do it this way rather than having a boolean option for enabling an
+# external private key, because 'make randconfig' might enable such a
+# boolean option and we unfortunately can't make it depend on !RANDCONFIG.
+ifeq ($(CONFIG_MODULE_SIG_KEY),"signing_key.priv")
signing_key.priv signing_key.x509: x509.genkey
@echo "###"
@echo "### Now generating an X.509 key pair to be used for signing modules."
@@ -207,3 +211,4 @@ x509.genkey:
@echo >>x509.genkey "subjectKeyIdentifier=hash"
@echo >>x509.genkey "authorityKeyIdentifier=keyid"
endif
+endif
--
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