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David Woodhousedhowells
David Woodhouse
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dhowells
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modsign: Extract signing cert from CONFIG_MODULE_SIG_KEY if needed
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>
1 parent 19e91b6 commit 1329e8c

5 files changed

Lines changed: 181 additions & 11 deletions

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‎Documentation/module-signing.txt‎

Lines changed: 5 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -93,17 +93,16 @@ This has a number of options available:
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Setting this option to something other than its default of
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"signing_key.priv" will disable the autogeneration of signing keys and
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allow the kernel modules to be signed with a key of your choosing.
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The string provided should identify a file containing a private key
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in PEM form, or — on systems where the OpenSSL ENGINE_pkcs11 is
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appropriately installed — a PKCS#11 URI as defined by RFC7512.
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The string provided should identify a file containing both a private
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key and its corresponding X.509 certificate in PEM form, or — on
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systems where the OpenSSL ENGINE_pkcs11 is functional — a PKCS#11 URI
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as defined by RFC7512. In the latter case, the PKCS#11 URI should
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reference both a certificate and a private key.
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If the PEM file containing the private key is encrypted, or if the
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PKCS#11 token requries a PIN, this can be provided at build time by
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means of the KBUILD_SIGN_PIN variable.
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The corresponding X.509 certificate in DER form should still be placed
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in a file named signing_key.x509 in the top-level build directory.
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=======================
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GENERATING SIGNING KEYS

‎init/Kconfig‎

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1953,10 +1953,10 @@ config MODULE_SIG_KEY
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default "signing_key.priv"
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depends on MODULE_SIG
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help
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Provide the file name of a private key in PKCS#8 PEM format, or
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a PKCS#11 URI according to RFC7512. The corresponding X.509
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certificate in DER form should be present in signing_key.x509
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in the top-level build directory.
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Provide the file name of a private key/certificate in PEM format,
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or a PKCS#11 URI according to RFC7512. The file should contain, or
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the URI should identify, both the certificate and its corresponding
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private key.
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If this option is unchanged from its default "signing_key.priv",
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then the kernel will automatically generate the private key and

‎kernel/Makefile‎

Lines changed: 38 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -210,5 +210,43 @@ x509.genkey:
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@echo >>x509.genkey "keyUsage=digitalSignature"
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@echo >>x509.genkey "subjectKeyIdentifier=hash"
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@echo >>x509.genkey "authorityKeyIdentifier=keyid"
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else
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# For external (PKCS#11 or PEM) key, we need to obtain the certificate from
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# CONFIG_MODULE_SIG_KEY automatically.
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quiet_cmd_extract_der = CERT_DER $(2)
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cmd_extract_der = scripts/extract-cert "$(2)" signing_key.x509
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# CONFIG_MODULE_SIG_KEY is either a PKCS#11 URI or a filename. It is
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# surrounded by quotes, and may contain spaces. To strip the quotes
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# with $(patsubst) we need to turn the spaces into something else.
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# And if it's a filename, those spaces need to be escaped as '\ ' in
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# order to use it in dependencies or $(wildcard).
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space :=
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space +=
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space_escape := %%%SPACE%%%
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X509_SOURCE_temp := $(subst $(space),$(space_escape),$(CONFIG_MODULE_SIG_KEY))
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# We need this to check for absolute paths or PKCS#11 URIs.
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X509_SOURCE_ONEWORD := $(patsubst "%",%,$(X509_SOURCE_temp))
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# This is the actual source filename/URI without the quotes
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X509_SOURCE := $(subst $(space_escape),$(space),$(X509_SOURCE_ONEWORD))
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# This\ version\ with\ spaces\ escaped\ for\ $(wildcard)\ and\ dependencies
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X509_SOURCE_ESCAPED := $(subst $(space_escape),\$(space),$(X509_SOURCE_ONEWORD))
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ifeq ($(patsubst pkcs11:%,%,$(X509_SOURCE_ONEWORD)),$(X509_SOURCE_ONEWORD))
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# If it's a filename, depend on it.
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X509_DEP := $(X509_SOURCE_ESCAPED)
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ifeq ($(patsubst /%,%,$(X509_SOURCE_ONEWORD)),$(X509_SOURCE_ONEWORD))
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ifeq ($(wildcard $(X509_SOURCE_ESCAPED)),)
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ifneq ($(wildcard $(srctree)/$(X509_SOURCE_ESCAPED)),)
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# Non-absolute filename, found in source tree and not build tree
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X509_SOURCE := $(srctree)/$(X509_SOURCE)
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X509_DEP := $(srctree)/$(X509_SOURCE_ESCAPED)
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endif
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endif
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endif
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endif
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signing_key.x509: scripts/extract-cert include/config/module/sig/key.h $(X509_DEP)
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$(call cmd,extract_der,$(X509_SOURCE))
213251
endif
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endif

‎scripts/Makefile‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -16,11 +16,12 @@ hostprogs-$(CONFIG_VT) += conmakehash
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hostprogs-$(BUILD_C_RECORDMCOUNT) += recordmcount
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hostprogs-$(CONFIG_BUILDTIME_EXTABLE_SORT) += sortextable
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hostprogs-$(CONFIG_ASN1) += asn1_compiler
19-
hostprogs-$(CONFIG_MODULE_SIG) += sign-file
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hostprogs-$(CONFIG_MODULE_SIG) += sign-file extract-cert
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HOSTCFLAGS_sortextable.o = -I$(srctree)/tools/include
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HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include
2323
HOSTLOADLIBES_sign-file = -lcrypto
24+
HOSTLOADLIBES_extract-cert = -lcrypto
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2526
always := $(hostprogs-y) $(hostprogs-m)
2627

‎scripts/extract-cert.c‎

Lines changed: 132 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,132 @@
1+
/* Extract X.509 certificate in DER form from PKCS#11 or PEM.
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*
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* Copyright © 2014 Red Hat, Inc. All Rights Reserved.
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* Copyright © 2015 Intel Corporation.
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*
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* Authors: David Howells <dhowells@redhat.com>
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* David Woodhouse <dwmw2@infradead.org>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#define _GNU_SOURCE
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <stdbool.h>
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#include <string.h>
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#include <getopt.h>
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#include <err.h>
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#include <arpa/inet.h>
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#include <openssl/bio.h>
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#include <openssl/evp.h>
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#include <openssl/pem.h>
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#include <openssl/pkcs7.h>
27+
#include <openssl/err.h>
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#include <openssl/engine.h>
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30+
#define PKEY_ID_PKCS7 2
31+
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static __attribute__((noreturn))
33+
void format(void)
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{
35+
fprintf(stderr,
36+
"Usage: scripts/extract-cert <source> <dest>\n");
37+
exit(2);
38+
}
39+
40+
static void display_openssl_errors(int l)
41+
{
42+
const char *file;
43+
char buf[120];
44+
int e, line;
45+
46+
if (ERR_peek_error() == 0)
47+
return;
48+
fprintf(stderr, "At main.c:%d:\n", l);
49+
50+
while ((e = ERR_get_error_line(&file, &line))) {
51+
ERR_error_string(e, buf);
52+
fprintf(stderr, "- SSL %s: %s:%d\n", buf, file, line);
53+
}
54+
}
55+
56+
static void drain_openssl_errors(void)
57+
{
58+
const char *file;
59+
int line;
60+
61+
if (ERR_peek_error() == 0)
62+
return;
63+
while (ERR_get_error_line(&file, &line)) {}
64+
}
65+
66+
#define ERR(cond, fmt, ...) \
67+
do { \
68+
bool __cond = (cond); \
69+
display_openssl_errors(__LINE__); \
70+
if (__cond) { \
71+
err(1, fmt, ## __VA_ARGS__); \
72+
} \
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} while(0)
74+
75+
static const char *key_pass;
76+
77+
int main(int argc, char **argv)
78+
{
79+
char *cert_src, *cert_dst;
80+
X509 *x509;
81+
BIO *b;
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83+
OpenSSL_add_all_algorithms();
84+
ERR_load_crypto_strings();
85+
ERR_clear_error();
86+
87+
key_pass = getenv("KBUILD_SIGN_PIN");
88+
89+
if (argc != 3)
90+
format();
91+
92+
cert_src = argv[1];
93+
cert_dst = argv[2];
94+
95+
if (!strncmp(cert_src, "pkcs11:", 7)) {
96+
ENGINE *e;
97+
struct {
98+
const char *cert_id;
99+
X509 *cert;
100+
} parms;
101+
102+
parms.cert_id = cert_src;
103+
parms.cert = NULL;
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105+
ENGINE_load_builtin_engines();
106+
drain_openssl_errors();
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e = ENGINE_by_id("pkcs11");
108+
ERR(!e, "Load PKCS#11 ENGINE");
109+
if (ENGINE_init(e))
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drain_openssl_errors();
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else
112+
ERR(1, "ENGINE_init");
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if (key_pass)
114+
ERR(!ENGINE_ctrl_cmd_string(e, "PIN", key_pass, 0), "Set PKCS#11 PIN");
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ENGINE_ctrl_cmd(e, "LOAD_CERT_CTRL", 0, &parms, NULL, 1);
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ERR(!parms.cert, "Get X.509 from PKCS#11");
117+
x509 = parms.cert;
118+
} else {
119+
b = BIO_new_file(cert_src, "rb");
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ERR(!b, "%s", cert_src);
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x509 = PEM_read_bio_X509(b, NULL, NULL, NULL);
122+
ERR(!x509, "%s", cert_src);
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BIO_free(b);
124+
}
125+
126+
b = BIO_new_file(cert_dst, "wb");
127+
ERR(!b, "%s", cert_dst);
128+
ERR(!i2d_X509_bio(b, x509), cert_dst);
129+
BIO_free(b);
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return 0;
132+
}

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