From 4dbf0d7281b6c9dfb130e4264d1e37c27124a599 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Micka=C3=ABl=20Sala=C3=BCn?= Date: Mon, 12 Jul 2021 19:03:10 +0200 Subject: [PATCH] certs: Check that builtin blacklist hashes are valid MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Add and use a check-blacklist-hashes.awk script to make sure that the builtin blacklist hashes set with CONFIG_SYSTEM_BLACKLIST_HASH_LIST will effectively be taken into account as blacklisted hashes. This is useful to debug invalid hash formats, and it make sure that previous hashes which could have been loaded in the kernel, but silently ignored, are now noticed and deal with by the user at kernel build time. This also prevent stricter blacklist key description checking (provided by following commits) to failed for builtin hashes. Update CONFIG_SYSTEM_BLACKLIST_HASH_LIST help to explain the content of a hash string and how to generate certificate ones. Cc: David Howells Cc: David Woodhouse Cc: Eric Snowberg Cc: Jarkko Sakkinen Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20210712170313.884724-3-mic@digikod.net Reviewed-by: Jarkko Sakkinen Signed-off-by: Jarkko Sakkinen --- MAINTAINERS | 1 + certs/.gitignore | 1 + certs/Kconfig | 7 ++++-- certs/Makefile | 14 ++++++++++- scripts/check-blacklist-hashes.awk | 37 ++++++++++++++++++++++++++++++ 5 files changed, 57 insertions(+), 3 deletions(-) create mode 100755 scripts/check-blacklist-hashes.awk diff --git a/MAINTAINERS b/MAINTAINERS index 4f2a63b0ec3bf..bf41a67635ec4 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -4575,6 +4575,7 @@ L: keyrings@vger.kernel.org S: Maintained F: Documentation/admin-guide/module-signing.rst F: certs/ +F: scripts/check-blacklist-hashes.awk F: scripts/sign-file.c F: tools/certs/ diff --git a/certs/.gitignore b/certs/.gitignore index 9e42fe3e02f56..56637aceaf81c 100644 --- a/certs/.gitignore +++ b/certs/.gitignore @@ -1,4 +1,5 @@ # SPDX-License-Identifier: GPL-2.0-only +/blacklist_hashes_checked /extract-cert /x509_certificate_list /x509_revocation_list diff --git a/certs/Kconfig b/certs/Kconfig index 73d1350c223a8..4bd385b250848 100644 --- a/certs/Kconfig +++ b/certs/Kconfig @@ -104,8 +104,11 @@ config SYSTEM_BLACKLIST_HASH_LIST help If set, this option should be the filename of a list of hashes in the form "", "", ... . This will be included into a C - wrapper to incorporate the list into the kernel. Each should - be a string of hex digits. + wrapper to incorporate the list into the kernel. Each must be a + string starting with a prefix ("tbs" or "bin"), then a colon (":"), and + finally an even number of hexadecimal lowercase characters (up to 128). + Certificate hashes can be generated with + tools/certs/print-cert-tbs-hash.sh . config SYSTEM_REVOCATION_LIST bool "Provide system-wide ring of revocation certificates" diff --git a/certs/Makefile b/certs/Makefile index d8443cfb1c401..1d26ae36af20d 100644 --- a/certs/Makefile +++ b/certs/Makefile @@ -7,6 +7,18 @@ obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o c obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist.o common.o obj-$(CONFIG_SYSTEM_REVOCATION_LIST) += revocation_certificates.o ifneq ($(CONFIG_SYSTEM_BLACKLIST_HASH_LIST),) +quiet_cmd_check_blacklist_hashes = CHECK $(patsubst "%",%,$(2)) + cmd_check_blacklist_hashes = $(AWK) -f $(srctree)/scripts/check-blacklist-hashes.awk $(2); touch $@ + +$(eval $(call config_filename,SYSTEM_BLACKLIST_HASH_LIST)) + +$(obj)/blacklist_hashes.o: $(obj)/blacklist_hashes_checked + +CFLAGS_blacklist_hashes.o += -I$(srctree) + +targets += blacklist_hashes_checked +$(obj)/blacklist_hashes_checked: $(SYSTEM_BLACKLIST_HASH_LIST_SRCPREFIX)$(SYSTEM_BLACKLIST_HASH_LIST_FILENAME) scripts/check-blacklist-hashes.awk FORCE + $(call if_changed,check_blacklist_hashes,$(SYSTEM_BLACKLIST_HASH_LIST_SRCPREFIX)$(CONFIG_SYSTEM_BLACKLIST_HASH_LIST)) obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist_hashes.o else obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist_nohashes.o @@ -21,7 +33,7 @@ $(obj)/system_certificates.o: $(obj)/x509_certificate_list $(obj)/x509_certificate_list: $(CONFIG_SYSTEM_TRUSTED_KEYS) $(obj)/extract-cert FORCE $(call if_changed,extract_certs) -targets += x509_certificate_list +targets += x509_certificate_list blacklist_hashes_checked # If module signing is requested, say by allyesconfig, but a key has not been # supplied, then one will need to be generated to make sure the build does not diff --git a/scripts/check-blacklist-hashes.awk b/scripts/check-blacklist-hashes.awk new file mode 100755 index 0000000000000..107c1d3204d47 --- /dev/null +++ b/scripts/check-blacklist-hashes.awk @@ -0,0 +1,37 @@ +#!/usr/bin/awk -f +# SPDX-License-Identifier: GPL-2.0 +# +# Copyright © 2020, Microsoft Corporation. All rights reserved. +# +# Author: Mickaël Salaün +# +# Check that a CONFIG_SYSTEM_BLACKLIST_HASH_LIST file contains a valid array of +# hash strings. Such string must start with a prefix ("tbs" or "bin"), then a +# colon (":"), and finally an even number of hexadecimal lowercase characters +# (up to 128). + +BEGIN { + RS = "," +} +{ + if (!match($0, "^[ \t\n\r]*\"([^\"]*)\"[ \t\n\r]*$", part1)) { + print "Not a string (item " NR "):", $0; + exit 1; + } + if (!match(part1[1], "^(tbs|bin):(.*)$", part2)) { + print "Unknown prefix (item " NR "):", part1[1]; + exit 1; + } + if (!match(part2[2], "^([0-9a-f]+)$", part3)) { + print "Not a lowercase hexadecimal string (item " NR "):", part2[2]; + exit 1; + } + if (length(part3[1]) > 128) { + print "Hash string too long (item " NR "):", part3[1]; + exit 1; + } + if (length(part3[1]) % 2 == 1) { + print "Not an even number of hexadecimal characters (item " NR "):", part3[1]; + exit 1; + } +} -- 2.39.5