MODSIGN: Sign modules during the build process

If CONFIG_MODULE_SIG is set, then this patch will cause all modules files to
to have signatures added.  The following steps will occur:

 (1) The module will be linked to foo.ko.unsigned instead of foo.ko

 (2) The module will be stripped using both "strip -x -g" and "eu-strip" to
     ensure minimal size for inclusion in an initramfs.

 (3) The signature will be generated on the stripped module.

 (4) The signature will be appended to the module, along with some information
     about the signature and a magic string that indicates the presence of the
     signature.

Step (3) requires private and public keys to be available.  By default these
are expected to be found in files:

	signing_key.priv
	signing_key.x509

in the base directory of the build.  The first is the private key in PEM form
and the second is the X.509 certificate in DER form as can be generated from
openssl:

	openssl req \
		-new -x509 -outform PEM -out signing_key.x509 \
		-keyout signing_key.priv -nodes \
		-subj "/CN=H2G2/O=Magrathea/CN=Slartibartfast"

If the secret key is not found then signing will be skipped and the unsigned
module from (1) will just be copied to foo.ko.

If signing occurs, lines like the following will be seen:

	LD [M]  fs/foo/foo.ko.unsigned
	STRIP [M] fs/foo/foo.ko.stripped
	SIGN [M] fs/foo/foo.ko

will appear in the build log.  If the signature step will be skipped and the
following will be seen:

	LD [M]  fs/foo/foo.ko.unsigned
	STRIP [M] fs/foo/foo.ko.stripped
	NO SIGN [M] fs/foo/foo.ko

NOTE!  After the signature step, the signed module _must_not_ be passed through
strip.  The unstripped, unsigned module is still available at the name on the
LD [M] line.  This restriction may affect packaging tools (such as rpmbuild)
and initramfs composition tools.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

2 files changed, 191 insertions, 1 deletions

diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 08dce14..2a4d1a1 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -14,7 +14,8 @@
 # 3)  create one <module>.mod.c file pr. module
 # 4)  create one Module.symvers file with CRC for all exported symbols
 # 5) compile all <module>.mod.c files
-# 6) final link of the module to a <module.ko> file
+# 6) final link of the module to a <module.ko> (or <module.unsigned>) file
+# 7) signs the modules to a <module.ko> file
 
 # Step 3 is used to place certain information in the module's ELF
 # section, including information such as:
@@ -32,6 +33,8 @@
 # Step 4 is solely used to allow module versioning in external modules,
 # where the CRC of each module is retrieved from the Module.symvers file.
 
+# Step 7 is dependent on CONFIG_MODULE_SIG being enabled.
+
 # KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined
 # symbols in the final module linking stage
 # KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
@@ -116,6 +119,7 @@ $(modules:.ko=.mod.o): %.mod.o: %.mod.c FORCE
 targets += $(modules:.ko=.mod.o)
 
 # Step 6), final link of the modules
+ifneq ($(CONFIG_MODULE_SIG),y)
 quiet_cmd_ld_ko_o = LD [M]  $@
       cmd_ld_ko_o = $(LD) -r $(LDFLAGS)                                 \
                              $(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \
@@ -125,7 +129,78 @@ $(modules): %.ko :%.o %.mod.o FORCE
 	$(call if_changed,ld_ko_o)
 
 targets += $(modules)
+else
+quiet_cmd_ld_ko_unsigned_o = LD [M]  $@
+      cmd_ld_ko_unsigned_o =						\
+		$(LD) -r $(LDFLAGS)					\
+			 $(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE)	\
+			 -o $@ $(filter-out FORCE,$^)			\
+		$(if $(AFTER_LINK),; $(AFTER_LINK))
+
+$(modules:.ko=.ko.unsigned): %.ko.unsigned :%.o %.mod.o FORCE
+	$(call if_changed,ld_ko_unsigned_o)
+
+targets += $(modules:.ko=.ko.unsigned)
+
+# Step 7), sign the modules
+MODSECKEY = ./signing_key.priv
+MODPUBKEY = ./signing_key.x509
+
+ifeq ($(wildcard $(MODSECKEY))+$(wildcard $(MODPUBKEY)),$(MODSECKEY)+$(MODPUBKEY))
+ifeq ($(KBUILD_SRC),)
+	# no O= is being used
+	SCRIPTS_DIR := scripts
+else
+	SCRIPTS_DIR := $(KBUILD_SRC)/scripts
+endif
+SIGN_MODULES := 1
+else
+SIGN_MODULES := 0
+endif
+
+# only sign if it's an in-tree module
+ifneq ($(KBUILD_EXTMOD),)
+SIGN_MODULES := 0
+endif
 
+# We strip the module as best we can - note that using both strip and eu-strip
+# results in a smaller module than using either alone.
+EU_STRIP = $(shell which eu-strip || echo true)
+
+quiet_cmd_sign_ko_stripped_ko_unsigned = STRIP [M] $@
+      cmd_sign_ko_stripped_ko_unsigned = \
+		cp $< $@ && \
+		strip -x -g $@ && \
+		$(EU_STRIP) $@
+
+ifeq ($(SIGN_MODULES),1)
+
+quiet_cmd_genkeyid = GENKEYID $@
+      cmd_genkeyid = \
+		perl $(SCRIPTS_DIR)/x509keyid $< $<.signer $<.keyid
+
+%.signer %.keyid: %
+	$(call if_changed,genkeyid)
+
+KEYRING_DEP := $(MODSECKEY) $(MODPUBKEY) $(MODPUBKEY).signer $(MODPUBKEY).keyid
+quiet_cmd_sign_ko_ko_stripped = SIGN [M] $@
+      cmd_sign_ko_ko_stripped = \
+		sh $(SCRIPTS_DIR)/sign-file $(MODSECKEY) $(MODPUBKEY) $< $@
+else
+KEYRING_DEP :=
+quiet_cmd_sign_ko_ko_unsigned = NO SIGN [M] $@
+      cmd_sign_ko_ko_unsigned = \
+		cp $< $@
+endif
+
+$(modules): %.ko :%.ko.stripped $(KEYRING_DEP) FORCE
+	$(call if_changed,sign_ko_ko_stripped)
+
+$(patsubst %.ko,%.ko.stripped,$(modules)): %.ko.stripped :%.ko.unsigned FORCE
+	$(call if_changed,sign_ko_stripped_ko_unsigned)
+
+targets += $(modules)
+endif
 
 # Add FORCE to the prequisites of a target to force it to be always rebuilt.
 # ---------------------------------------------------------------------------
diff --git a/scripts/sign-file b/scripts/sign-file
new file mode 100644
index 0000000..e58e34e
--- /dev/null
+++ b/scripts/sign-file
@@ -0,0 +1,115 @@
+#!/bin/sh
+#
+# Sign a module file using the given key.
+#
+# Format: sign-file <key> <x509> <src-file> <dst-file>
+#
+
+scripts=`dirname $0`
+
+CONFIG_MODULE_SIG_SHA512=y
+if [ -r .config ]
+then
+    . ./.config
+fi
+
+key="$1"
+x509="$2"
+src="$3"
+dst="$4"
+
+if [ ! -r "$key" ]
+then
+    echo "Can't read private key" >&2
+    exit 2
+fi
+
+if [ ! -r "$x509" ]
+then
+    echo "Can't read X.509 certificate" >&2
+    exit 2
+fi
+if [ ! -r "$x509.signer" ]
+then
+    echo "Can't read Signer name" >&2
+    exit 2;
+fi
+if [ ! -r "$x509.keyid" ]
+then
+    echo "Can't read Key identifier" >&2
+    exit 2;
+fi
+
+#
+# Signature parameters
+#
+algo=1		# Public-key crypto algorithm: RSA
+hash=		# Digest algorithm
+id_type=1	# Identifier type: X.509
+
+#
+# Digest the data
+#
+dgst=
+if [ "$CONFIG_MODULE_SIG_SHA1" = "y" ]
+then
+    prologue="0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2B, 0x0E, 0x03, 0x02, 0x1A, 0x05, 0x00, 0x04, 0x14"
+    dgst=-sha1
+    hash=2
+elif [ "$CONFIG_MODULE_SIG_SHA224" = "y" ]
+then
+    prologue="0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04, 0x05, 0x00, 0x04, 0x1C"
+    dgst=-sha224
+    hash=7
+elif [ "$CONFIG_MODULE_SIG_SHA256" = "y" ]
+then
+    prologue="0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20"
+    dgst=-sha256
+    hash=4
+elif [ "$CONFIG_MODULE_SIG_SHA384" = "y" ]
+then
+    prologue="0x30, 0x41, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02, 0x05, 0x00, 0x04, 0x30"
+    dgst=-sha384
+    hash=5
+elif [ "$CONFIG_MODULE_SIG_SHA512" = "y" ]
+then
+    prologue="0x30, 0x51, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, 0x05, 0x00, 0x04, 0x40"
+    dgst=-sha512
+    hash=6
+else
+    echo "$0: Can't determine hash algorithm" >&2
+    exit 2
+fi
+
+(
+perl -e "binmode STDOUT; print pack(\"C*\", $prologue)" || exit $?
+openssl dgst $dgst -binary $src || exit $?
+) >$src.dig || exit $?
+
+#
+# Generate the binary signature, which will be just the integer that comprises
+# the signature with no metadata attached.
+#
+openssl rsautl -sign -inkey $key -keyform PEM -in $src.dig -out $src.sig || exit $?
+signerlen=`stat -c %s $x509.signer`
+keyidlen=`stat -c %s $x509.keyid`
+siglen=`stat -c %s $src.sig`
+
+#
+# Build the signed binary
+#
+(
+    cat $src || exit $?
+    echo '~Module signature appended~' || exit $?
+    cat $x509.signer $x509.keyid || exit $?
+
+    # Preface each signature integer with a 2-byte BE length
+    perl -e "binmode STDOUT; print pack(\"n\", $siglen)" || exit $?
+    cat $src.sig || exit $?
+
+    # Generate the information block
+    perl -e "binmode STDOUT; print pack(\"CCCCCxxxN\", $algo, $hash, $id_type, $signerlen, $keyidlen, $siglen + 2)" || exit $?
+) >$dst~ || exit $?
+
+# Permit in-place signing
+mv $dst~ $dst || exit $?