> On Mar 12, 2021, at 10:12 AM, Mickaël Salaün <mic@xxxxxxxxxxx> wrote: > > From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> > > Add a new helper print-cert-tbs-hash.sh to generate a TBSCertificate > hash from a given certificate. This is useful to generate a blacklist > key description used to forbid loading a specific certificate in a > keyring, or to invalidate a certificate provided by a PKCS#7 file. > > This kind of hash formatting is required to populate the file pointed > out by CONFIG_SYSTEM_BLACKLIST_HASH_LIST, but only the kernel code was > available to understand how to effectively create such hash. > > Cc: David Howells <dhowells@xxxxxxxxxx> > Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx> > Cc: Eric Snowberg <eric.snowberg@xxxxxxxxxx> > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> > Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx> > Link: https://lore.kernel.org/r/20210312171232.2681989-2-mic@xxxxxxxxxxx Tested-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx> > --- > > Changes since v5: > * Add Reviewed-by Jarkko. > > Changes since v3: > * Explain in the commit message that this kind of formating is not new > but it wasn't documented. > > Changes since v1: > * Fix typo. > * Use "if" block instead of "||" . > --- > MAINTAINERS | 1 + > tools/certs/print-cert-tbs-hash.sh | 91 ++++++++++++++++++++++++++++++ > 2 files changed, 92 insertions(+) > create mode 100755 tools/certs/print-cert-tbs-hash.sh > > diff --git a/MAINTAINERS b/MAINTAINERS > index 00836f6452f0..773a362e807f 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -4120,6 +4120,7 @@ F: Documentation/admin-guide/module-signing.rst > F: certs/ > F: scripts/extract-cert.c > F: scripts/sign-file.c > +F: tools/certs/ > > CFAG12864B LCD DRIVER > M: Miguel Ojeda Sandonis <miguel.ojeda.sandonis@xxxxxxxxx> > diff --git a/tools/certs/print-cert-tbs-hash.sh b/tools/certs/print-cert-tbs-hash.sh > new file mode 100755 > index 000000000000..c93df5387ec9 > --- /dev/null > +++ b/tools/certs/print-cert-tbs-hash.sh > @@ -0,0 +1,91 @@ > +#!/bin/bash > +# SPDX-License-Identifier: GPL-2.0 > +# > +# Copyright © 2020, Microsoft Corporation. All rights reserved. > +# > +# Author: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> > +# > +# Compute and print the To Be Signed (TBS) hash of a certificate. This is used > +# as description of keys in the blacklist keyring to identify certificates. > +# This output should be redirected, without newline, in a file (hash0.txt) and > +# signed to create a PKCS#7 file (hash0.p7s). Both of these files can then be > +# loaded in the kernel with. > +# > +# Exemple on a workstation: > +# ./print-cert-tbs-hash.sh certificate-to-invalidate.pem > hash0.txt > +# openssl smime -sign -in hash0.txt -inkey builtin-private-key.pem \ > +# -signer builtin-certificate.pem -certfile certificate-chain.pem \ > +# -noattr -binary -outform DER -out hash0.p7s > +# > +# Exemple on a managed system: > +# keyctl padd blacklist "$(< hash0.txt)" %:.blacklist < hash0.p7s > + > +set -u -e -o pipefail > + > +CERT="${1:-}" > +BASENAME="$(basename -- "${BASH_SOURCE[0]}")" > + > +if [ $# -ne 1 ] || [ ! -f "${CERT}" ]; then > + echo "usage: ${BASENAME} <certificate>" >&2 > + exit 1 > +fi > + > +# Checks that it is indeed a certificate (PEM or DER encoded) and exclude the > +# optional PEM text header. > +if ! PEM="$(openssl x509 -inform DER -in "${CERT}" 2>/dev/null || openssl x509 -in "${CERT}")"; then > + echo "ERROR: Failed to parse certificate" >&2 > + exit 1 > +fi > + > +# TBSCertificate starts at the second entry. > +# Cf. https://tools.ietf.org/html/rfc3280#section-4.1 > +# > +# Exemple of first lines printed by openssl asn1parse: > +# 0:d=0 hl=4 l= 763 cons: SEQUENCE > +# 4:d=1 hl=4 l= 483 cons: SEQUENCE > +# 8:d=2 hl=2 l= 3 cons: cont [ 0 ] > +# 10:d=3 hl=2 l= 1 prim: INTEGER :02 > +# 13:d=2 hl=2 l= 20 prim: INTEGER :3CEB2CB8818D968AC00EEFE195F0DF9665328B7B > +# 35:d=2 hl=2 l= 13 cons: SEQUENCE > +# 37:d=3 hl=2 l= 9 prim: OBJECT :sha256WithRSAEncryption > +RANGE_AND_DIGEST_RE=' > +2s/^\s*\([0-9]\+\):d=\s*[0-9]\+\s\+hl=\s*[0-9]\+\s\+l=\s*\([0-9]\+\)\s\+cons:\s*SEQUENCE\s*$/\1 \2/p; > +7s/^\s*[0-9]\+:d=\s*[0-9]\+\s\+hl=\s*[0-9]\+\s\+l=\s*[0-9]\+\s\+prim:\s*OBJECT\s*:\(.*\)$/\1/p; > +' > + > +RANGE_AND_DIGEST=($(echo "${PEM}" | \ > + openssl asn1parse -in - | \ > + sed -n -e "${RANGE_AND_DIGEST_RE}")) > + > +if [ "${#RANGE_AND_DIGEST[@]}" != 3 ]; then > + echo "ERROR: Failed to parse TBSCertificate." >&2 > + exit 1 > +fi > + > +OFFSET="${RANGE_AND_DIGEST[0]}" > +END="$(( OFFSET + RANGE_AND_DIGEST[1] ))" > +DIGEST="${RANGE_AND_DIGEST[2]}" > + > +# The signature hash algorithm is used by Linux to blacklist certificates. > +# Cf. crypto/asymmetric_keys/x509_cert_parser.c:x509_note_pkey_algo() > +DIGEST_MATCH="" > +while read -r DIGEST_ITEM; do > + if [ -z "${DIGEST_ITEM}" ]; then > + break > + fi > + if echo "${DIGEST}" | grep -qiF "${DIGEST_ITEM}"; then > + DIGEST_MATCH="${DIGEST_ITEM}" > + break > + fi > +done < <(openssl list -digest-commands | tr ' ' '\n' | sort -ur) > + > +if [ -z "${DIGEST_MATCH}" ]; then > + echo "ERROR: Unknown digest algorithm: ${DIGEST}" >&2 > + exit 1 > +fi > + > +echo "${PEM}" | \ > + openssl x509 -in - -outform DER | \ > + dd "bs=1" "skip=${OFFSET}" "count=${END}" "status=none" | \ > + openssl dgst "-${DIGEST_MATCH}" - | \ > + awk '{printf "tbs:" $2}' > -- > 2.30.2 >
