Re: [PATCH] MODSIGN: Change default key details [ver #2]

[Michal Marek <mmarek@suse.cz>]

On 2015-05-07 13:00, David Howells wrote:
> Michal Marek <mmarek@suse.cz> wrote:
> 
>> are you fine with these two patches?
>>
>>   https://lkml.org/lkml/2015/2/20/546
>>   https://lkml.org/lkml/2015/5/4/614
> 
> Yeah, I think so.  Your reasoning on the first one is sound - but is it
> possible for $(objtree) to != $(srctree) even when they're coincident.

This part is fine. $(objtee) is always '.', the variable is only used as
an annotation. You can of course do 'make O=/symlink/to/current/dir',
but this will fail with

  /your/current/dir is not clean, please run 'make mrproper'


> I like
> Linus's use of the filechk macro on the second - but we shouldn't overwrite
> keys someone has manually placed in the tree if the key generation template
> changes due to git pull altering kernel/Makefile.

That's the problem with allowing a file to be either user-supplied or
generated. We can use separate files for the user-supplied/generated
cases like below and solve this for good. Not signed off yet, because it
is only lightly tested and the clean rules and .gitignore need to be
updated.

Michal

>From aa68988b9b669f2c7d17466ba39e84d7e6617c34 Mon Sep 17 00:00:00 2001
From: Michal Marek <mmarek@suse.cz>
Date: Thu, 7 May 2015 13:38:23 +0200
Subject: [PATCH] MODSIGN: Split user-supplied and autogenerated signing key

Allow the users to place signing_key.{x509,priv} and x509.genkey in the
source tree. If any of these files is missing, generate the file in the
build tree with an .auto suffix. This avoids problems with overwriting
user-supplied files.
---
 Makefile        |  4 ++--
 kernel/Makefile | 46 +++++++++++++++++++++++-----------------------
 2 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/Makefile b/Makefile
index 19e256a..b4b8ef5 100644
--- a/Makefile
+++ b/Makefile
@@ -873,8 +873,8 @@ INITRD_COMPRESS-$(CONFIG_RD_LZ4)   := lz4
 # export INITRD_COMPRESS := $(INITRD_COMPRESS-y)
 
 ifdef CONFIG_MODULE_SIG_ALL
-MODSECKEY = ./signing_key.priv
-MODPUBKEY = ./signing_key.x509
+MODSECKEY = $(firstword $(wildcard $(srctree)/signing_key.priv),./signing_key.priv.auto)
+MODPUBKEY = $(firstword $(wildcard $(srctree)/signing_key.x509),./signing_key.x509.auto)
 export MODPUBKEY
 mod_sign_cmd = perl $(srctree)/scripts/sign-file $(CONFIG_MODULE_SIG_HASH) $(MODSECKEY) $(MODPUBKEY)
 else
diff --git a/kernel/Makefile b/kernel/Makefile
index e072239..4bcf20e 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -124,7 +124,7 @@ $(obj)/config_data.h: $(obj)/config_data.gz FORCE
 ###############################################################################
 ifeq ($(CONFIG_SYSTEM_TRUSTED_KEYRING),y)
 X509_CERTIFICATES-y := $(wildcard *.x509)
-X509_CERTIFICATES-$(CONFIG_MODULE_SIG) += signing_key.x509
+X509_CERTIFICATES-$(CONFIG_MODULE_SIG) += $(if $(wildcard $(srctree)/signing_key.x509),,signing_key.x509.auto)
 X509_CERTIFICATES := $(sort $(X509_CERTIFICATES-y))
 ifneq ($(objtree),$(srctree))
 X509_CERTIFICATES += $(sort $(wildcard $(srctree)/*.x509))
@@ -165,7 +165,7 @@ ifndef CONFIG_MODULE_SIG_HASH
 $(error Could not determine digest type to use from kernel config)
 endif
 
-signing_key.priv signing_key.x509: x509.genkey
+signing_key.priv.auto signing_key.x509.auto: $(firstword $(wildcard $(srctree)/x509.genkey) x509.genkey.auto)
 	@echo "###"
 	@echo "### Now generating an X.509 key pair to be used for signing modules."
 	@echo "###"
@@ -175,30 +175,30 @@ signing_key.priv signing_key.x509: x509.genkey
 	@echo "### number generator if one is available."
 	@echo "###"
 	openssl req -new -nodes -utf8 -$(CONFIG_MODULE_SIG_HASH) -days 36500 \
-		-batch -x509 -config x509.genkey \
-		-outform DER -out signing_key.x509 \
-		-keyout signing_key.priv 2>&1
+		-batch -x509 -config $< \
+		-outform DER -out signing_key.x509.auto \
+		-keyout signing_key.priv.auto 2>&1
 	@echo "###"
 	@echo "### Key pair generated."
 	@echo "###"
 
-x509.genkey:
+x509.genkey.auto:
 	@echo Generating X.509 key generation config
-	@echo  >x509.genkey "[ req ]"
-	@echo >>x509.genkey "default_bits = 4096"
-	@echo >>x509.genkey "distinguished_name = req_distinguished_name"
-	@echo >>x509.genkey "prompt = no"
-	@echo >>x509.genkey "string_mask = utf8only"
-	@echo >>x509.genkey "x509_extensions = myexts"
-	@echo >>x509.genkey
-	@echo >>x509.genkey "[ req_distinguished_name ]"
-	@echo >>x509.genkey "O = Magrathea"
-	@echo >>x509.genkey "CN = Glacier signing key"
-	@echo >>x509.genkey "emailAddress = slartibartfast@magrathea.h2g2"
-	@echo >>x509.genkey
-	@echo >>x509.genkey "[ myexts ]"
-	@echo >>x509.genkey "basicConstraints=critical,CA:FALSE"
-	@echo >>x509.genkey "keyUsage=digitalSignature"
-	@echo >>x509.genkey "subjectKeyIdentifier=hash"
-	@echo >>x509.genkey "authorityKeyIdentifier=keyid"
+	@echo  >$@ "[ req ]"
+	@echo >>$@ "default_bits = 4096"
+	@echo >>$@ "distinguished_name = req_distinguished_name"
+	@echo >>$@ "prompt = no"
+	@echo >>$@ "string_mask = utf8only"
+	@echo >>$@ "x509_extensions = myexts"
+	@echo >>$@
+	@echo >>$@ "[ req_distinguished_name ]"
+	@echo >>$@ "O = Magrathea"
+	@echo >>$@ "CN = Glacier signing key"
+	@echo >>$@ "emailAddress = slartibartfast@magrathea.h2g2"
+	@echo >>$@
+	@echo >>$@ "[ myexts ]"
+	@echo >>$@ "basicConstraints=critical,CA:FALSE"
+	@echo >>$@ "keyUsage=digitalSignature"
+	@echo >>$@ "subjectKeyIdentifier=hash"
+	@echo >>$@ "authorityKeyIdentifier=keyid"
 endif
-- 
2.1.4