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modsign: Extract signing cert from CONFIG_MODULE_SIG_KEY if needed

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Where an external PEM file or PKCS#11 URI is given, we can get the cert
from it for ourselves instead of making the user drop signing_key.x509
in place for us.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
David Woodhouse 2015-07-20 21:16:30 +01:00 committed by David Howells
parent 19e91b69d7
commit 1329e8cc69
5 changed files with 181 additions and 11 deletions
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11
Documentation/module-signing.txt
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@ -93,17 +93,16 @@ This has a number of options available:
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.
The string provided should identify a file containing both a private
key and its corresponding X.509 certificate in PEM form, or — on
systems where the OpenSSL ENGINE_pkcs11 is functional — a PKCS#11 URI
as defined by RFC7512. In the latter case, the PKCS#11 URI should
reference both a certificate and a private key.
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

8
init/Kconfig
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@ -1953,10 +1953,10 @@ config MODULE_SIG_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.
Provide the file name of a private key/certificate in PEM format,
or a PKCS#11 URI according to RFC7512. The file should contain, or
the URI should identify, both the certificate and its corresponding
private key.
If this option is unchanged from its default "signing_key.priv",
then the kernel will automatically generate the private key and

38
kernel/Makefile
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@ -210,5 +210,43 @@ x509.genkey:
@echo >>x509.genkey "keyUsage=digitalSignature"
@echo >>x509.genkey "subjectKeyIdentifier=hash"
@echo >>x509.genkey "authorityKeyIdentifier=keyid"
else
# For external (PKCS#11 or PEM) key, we need to obtain the certificate from
# CONFIG_MODULE_SIG_KEY automatically.
quiet_cmd_extract_der = CERT_DER $(2)
cmd_extract_der = scripts/extract-cert "$(2)" signing_key.x509
# CONFIG_MODULE_SIG_KEY is either a PKCS#11 URI or a filename. It is
# surrounded by quotes, and may contain spaces. To strip the quotes
# with $(patsubst) we need to turn the spaces into something else.
# And if it's a filename, those spaces need to be escaped as '\ ' in
# order to use it in dependencies or $(wildcard).
space :=
space +=
space_escape := %%%SPACE%%%
X509_SOURCE_temp := $(subst $(space),$(space_escape),$(CONFIG_MODULE_SIG_KEY))
# We need this to check for absolute paths or PKCS#11 URIs.
X509_SOURCE_ONEWORD := $(patsubst "%",%,$(X509_SOURCE_temp))
# This is the actual source filename/URI without the quotes
X509_SOURCE := $(subst $(space_escape),$(space),$(X509_SOURCE_ONEWORD))
# This\ version\ with\ spaces\ escaped\ for\ $(wildcard)\ and\ dependencies
X509_SOURCE_ESCAPED := $(subst $(space_escape),\$(space),$(X509_SOURCE_ONEWORD))
ifeq ($(patsubst pkcs11:%,%,$(X509_SOURCE_ONEWORD)),$(X509_SOURCE_ONEWORD))
# If it's a filename, depend on it.
X509_DEP := $(X509_SOURCE_ESCAPED)
ifeq ($(patsubst /%,%,$(X509_SOURCE_ONEWORD)),$(X509_SOURCE_ONEWORD))
ifeq ($(wildcard $(X509_SOURCE_ESCAPED)),)
ifneq ($(wildcard $(srctree)/$(X509_SOURCE_ESCAPED)),)
# Non-absolute filename, found in source tree and not build tree
X509_SOURCE := $(srctree)/$(X509_SOURCE)
X509_DEP := $(srctree)/$(X509_SOURCE_ESCAPED)
endif
endif
endif
endif
signing_key.x509: scripts/extract-cert include/config/module/sig/key.h $(X509_DEP)
$(call cmd,extract_der,$(X509_SOURCE))
endif
endif

3
scripts/Makefile
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@ -16,11 +16,12 @@ hostprogs-$(CONFIG_VT) += conmakehash
hostprogs-$(BUILD_C_RECORDMCOUNT) += recordmcount
hostprogs-$(CONFIG_BUILDTIME_EXTABLE_SORT) += sortextable
hostprogs-$(CONFIG_ASN1) += asn1_compiler
hostprogs-$(CONFIG_MODULE_SIG) += sign-file
hostprogs-$(CONFIG_MODULE_SIG) += sign-file extract-cert
HOSTCFLAGS_sortextable.o = -I$(srctree)/tools/include
HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include
HOSTLOADLIBES_sign-file = -lcrypto
HOSTLOADLIBES_extract-cert = -lcrypto
always := $(hostprogs-y) $(hostprogs-m)

132
scripts/extract-cert.c Normal file
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@ -0,0 +1,132 @@
/* Extract X.509 certificate in DER form from PKCS#11 or PEM.
*
* Copyright © 2014 Red Hat, Inc. All Rights Reserved.
* Copyright © 2015 Intel Corporation.
*
* Authors: David Howells <dhowells@redhat.com>
* David Woodhouse <dwmw2@infradead.org>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <getopt.h>
#include <err.h>
#include <arpa/inet.h>
#include <openssl/bio.h>
#include <openssl/evp.h>
#include <openssl/pem.h>
#include <openssl/pkcs7.h>
#include <openssl/err.h>
#include <openssl/engine.h>
#define PKEY_ID_PKCS7 2
static __attribute__((noreturn))
void format(void)
{
fprintf(stderr,
"Usage: scripts/extract-cert <source> <dest>\n");
exit(2);
}
static void display_openssl_errors(int l)
{
const char *file;
char buf[120];
int e, line;
if (ERR_peek_error() == 0)
return;
fprintf(stderr, "At main.c:%d:\n", l);
while ((e = ERR_get_error_line(&file, &line))) {
ERR_error_string(e, buf);
fprintf(stderr, "- SSL %s: %s:%d\n", buf, file, line);
}
}
static void drain_openssl_errors(void)
{
const char *file;
int line;
if (ERR_peek_error() == 0)
return;
while (ERR_get_error_line(&file, &line)) {}
}
#define ERR(cond, fmt, ...) \
do { \
bool __cond = (cond); \
display_openssl_errors(__LINE__); \
if (__cond) { \
err(1, fmt, ## __VA_ARGS__); \
} \
} while(0)
static const char *key_pass;
int main(int argc, char **argv)
{
char *cert_src, *cert_dst;
X509 *x509;
BIO *b;
OpenSSL_add_all_algorithms();
ERR_load_crypto_strings();
ERR_clear_error();
key_pass = getenv("KBUILD_SIGN_PIN");
if (argc != 3)
format();
cert_src = argv[1];
cert_dst = argv[2];
if (!strncmp(cert_src, "pkcs11:", 7)) {
ENGINE *e;
struct {
const char *cert_id;
X509 *cert;
} parms;
parms.cert_id = cert_src;
parms.cert = NULL;
ENGINE_load_builtin_engines();
drain_openssl_errors();
e = ENGINE_by_id("pkcs11");
ERR(!e, "Load PKCS#11 ENGINE");
if (ENGINE_init(e))
drain_openssl_errors();
else
ERR(1, "ENGINE_init");
if (key_pass)
ERR(!ENGINE_ctrl_cmd_string(e, "PIN", key_pass, 0), "Set PKCS#11 PIN");
ENGINE_ctrl_cmd(e, "LOAD_CERT_CTRL", 0, &parms, NULL, 1);
ERR(!parms.cert, "Get X.509 from PKCS#11");
x509 = parms.cert;
} else {
b = BIO_new_file(cert_src, "rb");
ERR(!b, "%s", cert_src);
x509 = PEM_read_bio_X509(b, NULL, NULL, NULL);
ERR(!x509, "%s", cert_src);
BIO_free(b);
}
b = BIO_new_file(cert_dst, "wb");
ERR(!b, "%s", cert_dst);
ERR(!i2d_X509_bio(b, x509), cert_dst);
BIO_free(b);
return 0;
}