Commit 80d65e58 authored by David Howells's avatar David Howells Committed by Rusty Russell

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: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 85ecac79
...@@ -14,7 +14,8 @@ ...@@ -14,7 +14,8 @@
# 3) create one <module>.mod.c file pr. module # 3) create one <module>.mod.c file pr. module
# 4) create one Module.symvers file with CRC for all exported symbols # 4) create one Module.symvers file with CRC for all exported symbols
# 5) compile all <module>.mod.c files # 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 # Step 3 is used to place certain information in the module's ELF
# section, including information such as: # section, including information such as:
...@@ -32,6 +33,8 @@ ...@@ -32,6 +33,8 @@
# Step 4 is solely used to allow module versioning in external modules, # 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. # 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 # KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined
# symbols in the final module linking stage # symbols in the final module linking stage
# KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules. # 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 ...@@ -116,6 +119,7 @@ $(modules:.ko=.mod.o): %.mod.o: %.mod.c FORCE
targets += $(modules:.ko=.mod.o) targets += $(modules:.ko=.mod.o)
# Step 6), final link of the modules # Step 6), final link of the modules
ifneq ($(CONFIG_MODULE_SIG),y)
quiet_cmd_ld_ko_o = LD [M] $@ quiet_cmd_ld_ko_o = LD [M] $@
cmd_ld_ko_o = $(LD) -r $(LDFLAGS) \ cmd_ld_ko_o = $(LD) -r $(LDFLAGS) \
$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \ $(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \
...@@ -125,7 +129,78 @@ $(modules): %.ko :%.o %.mod.o FORCE ...@@ -125,7 +129,78 @@ $(modules): %.ko :%.o %.mod.o FORCE
$(call if_changed,ld_ko_o) $(call if_changed,ld_ko_o)
targets += $(modules) 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. # Add FORCE to the prequisites of a target to force it to be always rebuilt.
# --------------------------------------------------------------------------- # ---------------------------------------------------------------------------
......
#!/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 $?
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