On Sun, Sep 12, 2021 at 10:59:25PM +0200, Roland Hieber wrote: > Signed-off-by: Roland Hieber <[email protected]> > --- > PATCH v3: > - adapt to cs_get_uri_impl from previous patch. cs_get_uri_unchecked > didn't really need to check for pkg_name anyway as it's only called > by cs_append_ca_from_uri in the code provider setup path, and the > code provider should always be able to get its own URI, so we can use > cs_get_uri_impl here too. > - cs_check_whitelist: handle the case correctly when the code signing > provider is not set up yet (i.e. when the BSP is built from scratch) > - small doc fixes > - use fixed whitelist filename, remove CODE_SIGNING_WHITELIST_FILENAME > (feedback by Michael Olbrich) > - remove superfluous backslash-newline escapes in multi-line defines > (feedback by Michael Olbrich) > - add early error handling for openssl | spki-hash in cs_append_ca_* > (feedback by Michael Olbrich) > - remove factually untrue comment in cs_append_ca_from_uri (feedback by > Michael Olbrich) > - use $(error) instead of $(ptx/error) (feedback by Michael Olbrich) > > PATCH v2: > https://lore.ptxdist.org/ptxdist/[email protected] > - cs_check_whitelisted: make "needle" a local variable (feedback by > Michael Olbrich) > - cs_check_whitelisted: error out with ERROR_KEY_NOT_WHITELISTED also > if whitelist does not exist yet (Michael Olbrich) > - rename cs_get_uri to cs_get_uri_unchecked and let cs_get_uri wrap it > instead of setting cs_no_whitelist_check=1 (Michael Olbrich) > - docs: simplify introductory example (Michael Olbrich) > - docs: add short paragraph on how to determine fingerprints of certs > > PATCH v1: > https://lore.ptxdist.org/ptxdist/[email protected] > --- > doc/daily_work.inc | 1 + > doc/dev_code_signing.rst | 77 +++++++++++++++++++++++ > platforms/code-signing.in | 10 +++ > rules/pre/030-code-signing-consumers.make | 6 ++ > scripts/lib/ptxd_lib_code_signing.sh | 56 ++++++++++++++++- > 5 files changed, 149 insertions(+), 1 deletion(-) > > diff --git a/doc/daily_work.inc b/doc/daily_work.inc > index 37bb9bc48180..a5b32dc5461c 100644 > --- a/doc/daily_work.inc > +++ b/doc/daily_work.inc > @@ -180,6 +180,7 @@ options during the `kernel.compile` and `kernel.install` > stages: > PTXdist supplies the URI from the ``kernel-modules`` role of the configured > code signing provider. > (The code signing provider should use :ref:`cs_set_uri` to set the URI.) > + The value of this kconfig option from your kernel config file is > overridden. > > However, additional settings must also be enabled in the kernel config: > > diff --git a/doc/dev_code_signing.rst b/doc/dev_code_signing.rst > index 413f694980eb..b0b8c9b4a3b8 100644 > --- a/doc/dev_code_signing.rst > +++ b/doc/dev_code_signing.rst > @@ -172,3 +172,80 @@ also via an environment variable. > (``=``, not ``:=``). > Otherwise the variable is expanded before a code signing provider can > perform > its setup. > + > +Key Whitelisting > +~~~~~~~~~~~~~~~~ > + > +In some use cases, it may be feasible to do additional checks to make sure > that > +a package uses the correct key material. > +For example, suppose you have a "release" code signing provider which you use > +to sign bootloaders for production, > +and a "development" code signing provider which you use to sign bootloaders > +with an extended feature set, e.g. to allow booting arbitrary kernels and > +userlands for debugging purposes. > +Your production boards are locked down in hardware so the ROM code only > +executes bootloaders signed with the "release" key. > +Now you don't want any bootloader with debugging features to be signed with a > +release key, otherwise someone could boot them on a locked-down production > +device, and use the additional debugging features to get extended access to > the > +production device. > +In this case, key whitelisting can help to prevent signing bootloader > packages > +with the wrong key. > + > +If the ``CODE_SIGNING_REQUIRE_WHITELIST`` kconfig symbol is enabled, > +the consumer functions :ref:`ptx/cs-get-ca` and :ref:`ptx/cs-get-uri` > +look up the triplet of package name, role name, and the pubkey's SHA256 > +fingerprint in ``configs/platform-<name>/code-signing-whitelist``. > +If a key or a CA is not whitelisted for the package in which it is to be > used, > +the functions will exit with an error message on the terminal:: > + > + $ ptxdist -v print KERNEL_MAKE_OPT > + ptxdist: error: SPKI whitelist record 'kernel kernel-modules > + 69C9BBB8BB4DFAE74AB21D06DFB5F2C67066373AE545453276847340822CDF04' not > found in > + distrokit/configs/platform-v7a/code-signing-whitelist > + > + …/ptxdist/rules/kernel.make:196: *** cs-get-uri: whitelist check failed, > see errors above. Stop. > + > +If ``CODE_SIGNING_REQUIRE_WHITELIST`` is disabled (the default), > +all keys and CAs are provided to all packages without further checks. > + > +The format of the code signing whitelist consists of one triplet per line, in > +which the elements of the triplet are separated by whitespace. > +If a CA is to be checked, the role name is prefixed with a literal ``ca:``, > +and the fingerprint refers to the public key of the certificate. > +All other unmatched lines in the file are ignored, but we suggest to use > ``#`` > +to start a line comment so as not to add a whitelist record accidentally. > + > +For example, here is a whitelist for use with the *devel* code provider which > +allows all provided keys to be used by their respective consumers:: > + > + # format: package-name role-name sha256-pubkey-fingerprint > + kernel kernel-modules > 69C9BBB8BB4DFAE74AB21D06DFB5F2C67066373AE545453276847340822CDF04 > + image-rauc update > 0034F8FE5ADC3B0DFE642407275D144DE2398C68CC9A86DD6703D7151116B44E > + image-rauc ca:update > 0034F8FE5ADC3B0DFE642407275D144DE2398C68CC9A86DD6703D7151116B44E > + rauc ca:update > 0034F8FE5ADC3B0DFE642407275D144DE2398C68CC9A86DD6703D7151116B44E > + > +.. note:: The match is case-sensitive, and the fingerprints are expected > + in uppercase. > + > + If a CA consists of more than one certificate, all of their fingerprints > + must be whitelisted. > + > +You can determine the key fingerprints by copying it from the error message, > +or with the `spki-hash`__ tool from the ``host-extract-cert`` package, > +or with openssl:: > + > + $ openssl pkey -in keyfile.pem -pubout -outform der \ > + | openssl sha256 \ > + | tr 'a-z' 'A-Z' > + (STDIN)= 69C9BBB8BB4DFAE74AB21D06DFB5F2C67066373AE545453276847340822CDF04 > + > +or, in the case of certificates:: > + > + $ openssl x509 -noout -in cert.pem -pubkey \ > + | openssl pkey -pubin -inform pem -pubout -outform der \ > + | openssl sha256 \ > + | tr 'a-z' 'A-Z' > + (STDIN)= 0034F8FE5ADC3B0DFE642407275D144DE2398C68CC9A86DD6703D7151116B44E > + > +__ https://git.pengutronix.de/cgit/extract-cert/tree/spki-hash.c > diff --git a/platforms/code-signing.in b/platforms/code-signing.in > index 81f9ef6f3c9e..7fa46e644df7 100644 > --- a/platforms/code-signing.in > +++ b/platforms/code-signing.in > @@ -20,4 +20,14 @@ source "generated/code_signing_provider.in" > > endchoice > > +config CODE_SIGNING_REQUIRE_WHITELISTED_KEYS > + bool > + prompt "require whitelisted keys" > + help > + Every time a key from the code provider is used, check if the consumer > + is allowed to use it. > + > + Code signing consumers can depend on this option if they want to force > + the key whitelist check.
I think, where the whitelist is expected should be mentioned here as well. Michael > + > endif > diff --git a/rules/pre/030-code-signing-consumers.make > b/rules/pre/030-code-signing-consumers.make > index e2c6c868e0ee..24bfa1c9c815 100644 > --- a/rules/pre/030-code-signing-consumers.make > +++ b/rules/pre/030-code-signing-consumers.make > @@ -21,6 +21,9 @@ $(strip > $(call ptx/cs-consumer-env, $(1)) > cs_get_uri '$(strip $(2))' > ) > + $(if $(filter-out 0,$(.SHELLSTATUS)), > + $(error cs-get-uri: whitelist check failed – see errors above) > + ) > ) > endef > > @@ -33,5 +36,8 @@ $(strip > $(call ptx/cs-consumer-env, $(1)) > cs_get_ca '$(strip $(2))' > ) > + $(if $(filter-out 0,$(.SHELLSTATUS)), > + $(error cs-get-ca: whitelist check failed – see errors above) > + ) > ) > endef > diff --git a/scripts/lib/ptxd_lib_code_signing.sh > b/scripts/lib/ptxd_lib_code_signing.sh > index 8f35c276855f..fe819bcb07ae 100644 > --- a/scripts/lib/ptxd_lib_code_signing.sh > +++ b/scripts/lib/ptxd_lib_code_signing.sh > @@ -1,6 +1,7 @@ > #!/bin/bash > # > # Copyright (C) 2019 Sascha Hauer <[email protected]> > +# Copyright (C) 2020 Jan Luebbe <[email protected]> > # Copyright (C) 2021 Roland Hieber, Pengutronix <[email protected]> > # > # For further information about the PTXdist project and license conditions > @@ -145,6 +146,47 @@ cs_group_get_roles() { > } > export -f cs_group_get_roles > > +# > +# cs_check_whitelisted <role> <uri/pem or fingerprint prefixed with > "sha256:"> > +# > +# Checks if the SPKI (Subject Public Key Info) Hash is in the whitelist > +# > +cs_check_whitelisted() { > + local role="${1:-ERROR_ROLE_IS_EMPTY}" > + local src="${2}" > + cs_init_variables > + > + if [ "${src}" = "ERROR_URI_NOT_YET_SET" ]; then > + # skip check until the code signing provider has been set up > + return; > + fi > + > + if [ "$(ptxd_get_ptxconf PTXCONF_CODE_SIGNING_REQUIRE_WHITELISTED_KEYS)" > != "y" ]; then > + return > + fi > + > + if ! ptxd_in_path PTXDIST_PATH_PLATFORMCONFIGDIR > "code-signing-whitelist"; then > + echo ERROR_KEY_NOT_WHITELISTED > + ptxd_bailout "${pkg_name}: SPKI hash whitelist check for role '${role}' > (${src}) is required, but configs/<platform>/code-signing-whitelist is > missing." > + fi > + local whitelist_path="${ptxd_reply}" > + > + local hash > + if [ "${src#sha256:}" != "${src}" ]; then > + hash="${src#sha256:}" > + else > + hash=$(ptxd_exec_silent_stderr spki-hash "${src}") > + fi > + hash=${hash:-ERROR_HASH_IS_EMPTY} > + local needle="${pkg_name}\s\+${role}\s\+${hash}" > + > + if ! grep -q --line-regexp "${needle}" "${whitelist_path}"; then > + echo ERROR_KEY_NOT_WHITELISTED > + ptxd_bailout "SPKI whitelist record '${pkg_name} ${role} ${hash}' not > found in $(ptxd_print_path "${whitelist_path}")" > + fi > +} > +export -f cs_check_whitelisted > + > # > # cs_set_uri <role> <uri> > # > @@ -191,7 +233,12 @@ cs_get_uri() { > 'Use $(call ptx/cs-get-uri, <PKG>, <role>) instead.' > fi > > - cs_get_uri_impl "$@" > + local role="${1}" > + local uri=$(cs_get_uri_impl "${role}") > + > + if cs_check_whitelisted "${role}" "${uri}"; then > + echo "${uri}" > + fi > } > export -f cs_get_uri > > @@ -318,6 +365,9 @@ cs_get_ca() { > fi > > if [ -e "${ca}" ]; then > + while read fp; do > + cs_check_whitelisted "ca:${role}" "sha256:${fp}" > + done < "${keydir}/${role}/ca.fingerprints" > echo "${ca}" > fi > } > @@ -333,6 +383,10 @@ cs_append_ca_from_pem() { > local pem="${2}" > cs_init_variables > > + openssl x509 -in "${pem}" -inform pem -noout -pubkey | \ > + spki-hash /dev/stdin >> "${keydir}/${role}/ca.fingerprints" > + check_pipe_status || ptxd_bailout "Extracting SPKI hash from CA '${pem}' > failed" > + > cat "${pem}" >> "${keydir}/${role}/ca.pem" > # add new line in case ${pem} does not end with an EOL > echo >> "${keydir}/${role}/ca.pem" > -- > 2.30.2 > > > _______________________________________________ > ptxdist mailing list > [email protected] > To unsubscribe, send a mail with subject "unsubscribe" to > [email protected] -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ ptxdist mailing list [email protected] To unsubscribe, send a mail with subject "unsubscribe" to [email protected]
