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    Subject[PATCH v7 2/5] certs: Check that builtin blacklist hashes are valid
    Date
    From: Mickaël Salaün <mic@linux.microsoft.com>

    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 <dhowells@redhat.com>
    Cc: David Woodhouse <dwmw2@infradead.org>
    Cc: Eric Snowberg <eric.snowberg@oracle.com>
    Cc: Jarkko Sakkinen <jarkko@kernel.org>
    Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
    Link: https://lore.kernel.org/r/20210312171232.2681989-3-mic@digikod.net
    ---

    Changes since v5:
    * Rebase on keys-next and fix conflict as previously done by David
    Howells.
    * Enable to use a file path relative to the kernel source directory.
    This align with the handling of CONFIG_SYSTEM_TRUSTED_KEYS,
    CONFIG_MODULE_SIG_KEY and CONFIG_SYSTEM_REVOCATION_KEYS.

    Changes since v3:
    * Improve commit description.
    * Update CONFIG_SYSTEM_BLACKLIST_HASH_LIST help.
    * Remove Acked-by Jarkko Sakkinen because of the above changes.

    Changes since v2:
    * Add Jarkko's Acked-by.

    Changes since v1:
    * Prefix script path with $(scrtree)/ (suggested by David Howells).
    * Fix hexadecimal number check.
    ---
    MAINTAINERS | 1 +
    certs/.gitignore | 1 +
    certs/Kconfig | 7 ++++--
    certs/Makefile | 17 +++++++++++++-
    scripts/check-blacklist-hashes.awk | 37 ++++++++++++++++++++++++++++++
    5 files changed, 60 insertions(+), 3 deletions(-)
    create mode 100755 scripts/check-blacklist-hashes.awk

    diff --git a/MAINTAINERS b/MAINTAINERS
    index 773a362e807f..a18fd3d283c6 100644
    --- a/MAINTAINERS
    +++ b/MAINTAINERS
    @@ -4118,6 +4118,7 @@ L: keyrings@vger.kernel.org
    S: Maintained
    F: Documentation/admin-guide/module-signing.rst
    F: certs/
    +F: scripts/check-blacklist-hashes.awk
    F: scripts/extract-cert.c
    F: scripts/sign-file.c
    F: tools/certs/
    diff --git a/certs/.gitignore b/certs/.gitignore
    index 2a2483990686..42cc2ac24b93 100644
    --- a/certs/.gitignore
    +++ b/certs/.gitignore
    @@ -1,2 +1,3 @@
    # SPDX-License-Identifier: GPL-2.0-only
    +blacklist_hashes_checked
    x509_certificate_list
    diff --git a/certs/Kconfig b/certs/Kconfig
    index ab88d2a7f3c7..cf3740c1b22b 100644
    --- a/certs/Kconfig
    +++ b/certs/Kconfig
    @@ -80,8 +80,11 @@ config SYSTEM_BLACKLIST_HASH_LIST
    help
    If set, this option should be the filename of a list of hashes in the
    form "<hash>", "<hash>", ... . This will be included into a C
    - wrapper to incorporate the list into the kernel. Each <hash> should
    - be a string of hex digits.
    + wrapper to incorporate the list into the kernel. Each <hash> 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 b6db52ebf0be..61e82b8eacd2 100644
    --- a/certs/Makefile
    +++ b/certs/Makefile
    @@ -7,7 +7,22 @@ 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
    endif
    @@ -30,7 +45,7 @@ $(obj)/x509_certificate_list: scripts/extract-cert $(SYSTEM_TRUSTED_KEYS_SRCPREF
    $(call if_changed,extract_certs,$(SYSTEM_TRUSTED_KEYS_SRCPREFIX)$(CONFIG_SYSTEM_TRUSTED_KEYS))
    endif # CONFIG_SYSTEM_TRUSTED_KEYRING

    -clean-files := x509_certificate_list .x509.list x509_revocation_list
    +clean-files := x509_certificate_list .x509.list x509_revocation_list blacklist_hashes_checked

    ifeq ($(CONFIG_MODULE_SIG),y)
    ###############################################################################
    diff --git a/scripts/check-blacklist-hashes.awk b/scripts/check-blacklist-hashes.awk
    new file mode 100755
    index 000000000000..107c1d3204d4
    --- /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 <mic@linux.microsoft.com>
    +#
    +# 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;
    + }
    +}
    --
    2.30.2
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