Re: [gentoo-dev] [PATCH 2/2 v4] kernel-build.eclass: add USE="modules-sign"

[Andrew Ammerlaan <andrewammerlaan@gentoo.org>]

Version 4 (and that's the last one, I promise), makes this work with 
pkcs11 uri's as well. Tested with my Nitrokey, it is (unsurprisingly) 
incredibly slow but it works.



 From 70415544a4aea458039f1abbbf9c7e112de846f3 Mon Sep 17 00:00:00 2001
From: Andrew Ammerlaan <andrewammerlaan@gentoo.org>
Date: Thu, 15 Jun 2023 21:10:02 +0200
Subject: [PATCH] kernel-build.eclass: add IUSE="modules-sign"

- Enable module signing configure options if requested by the user.

- Define the user variables MODULES_SIGN_HASH and MODULES_SIGN_KEY.
For controlling the used hashing algorithm and allowing the use of
external keys. These variables are the same as in linux-mod-r1.eclass

- Warn the user if we are letting the kernel build system generate the 
signing
key. This key will end up binary packages. Plus external modules will 
have to
be resigned if gentoo-kernel is re-emerged (i.e. a new key was generated).

Bug: https://bugs.gentoo.org/814344
Bug: https://bugs.gentoo.org/881651
Signed-off-by: Andrew Ammerlaan <andrewammerlaan@gentoo.org>
---
  eclass/kernel-build.eclass | 90 +++++++++++++++++++++++++++++++++++++-
  1 file changed, 89 insertions(+), 1 deletion(-)

diff --git a/eclass/kernel-build.eclass b/eclass/kernel-build.eclass
index abfb01720817a..7d4e2133a04d2 100644
--- a/eclass/kernel-build.eclass
+++ b/eclass/kernel-build.eclass
@@ -43,6 +43,48 @@ BDEPEND="

  IUSE="+strip"

+# @ECLASS_VARIABLE: KERNEL_IUSE_MODULES_SIGN
+# @PRE_INHERIT
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# If set to a non-null value, adds IUSE=modules-sign and required
+# logic to manipulate the kernel config while respecting the
+# MODULES_SIGN_HASH and MODULES_SIGN_KEY user variables.
+
+# @ECLASS_VARIABLE: MODULES_SIGN_HASH
+# @USER_VARIABLE
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# Used with USE=modules-sign.  Can be set to hash algorithm to use
+# during signature generation (CONFIG_MODULE_SIG_SHA256).
+#
+# Valid values: sha512,sha384,sha256,sha224,sha1
+#
+# Default if unset: sha512
+
+# @ECLASS_VARIABLE: MODULES_SIGN_KEY
+# @USER_VARIABLE
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# Used with USE=modules-sign.  Can be set to the path of the private
+# key in PEM format to use, or a PKCS#11 URI (CONFIG_MODULE_SIG_KEY).
+#
+# If path is relative (e.g. "certs/name.pem"), it is assumed to be
+# relative to the kernel build directory being used.
+#
+# If the key requires a passphrase or PIN, the used kernel sign-file
+# utility recognizes the KBUILD_SIGN_PIN environment variable.  Be
+# warned that the package manager may store this value in binary
+# packages, database files, temporary files, and possibly logs.  This
+# eclass unsets the variable after use to mitigate the issue (notably
+# for shared binary packages), but use this with care.
+#
+# Default if unset: certs/signing_key.pem
+
+if [[ ${KERNEL_IUSE_MODULES_SIGN} ]]; then
+	IUSE+=" modules-sign"
+fi
+
  # @FUNCTION: kernel-build_src_configure
  # @DESCRIPTION:
  # Prepare the toolchain for building the kernel, get the default .config
@@ -259,6 +301,9 @@ kernel-build_src_install() {
  	dosym "../../../${kernel_dir}" "/lib/modules/${module_ver}/build"
  	dosym "../../../${kernel_dir}" "/lib/modules/${module_ver}/source"

+	# unset to at least be out of the environment file in, e.g. shared binpkgs
+	unset KBUILD_SIGN_PIN
+
  	save_config build/.config
  }

@@ -268,6 +313,26 @@ kernel-build_src_install() {
  kernel-build_pkg_postinst() {
  	kernel-install_pkg_postinst
  	savedconfig_pkg_postinst
+
+	if [[ ${KERNEL_IUSE_MODULES_SIGN} ]]; then
+		if use modules-sign && [[ -z ${MODULES_SIGN_KEY} ]]; then
+			ewarn
+			ewarn "MODULES_SIGN_KEY was not set, this means the kernel build system"
+			ewarn "automatically generated the signing key. This key was installed"
+			ewarn "in ${EROOT}/usr/src/linux-${PV}${KV_LOCALVERSION}/certs"
+			ewarn "and will also be included in any binary packages."
+			ewarn "Please take appropriate action to protect the key!"
+			ewarn
+			ewarn "Recompiling this package causes a new key to be generated. As"
+			ewarn "a result any external kernel modules will need to be resigned."
+			ewarn "Use emerge @module-rebuild, or manually sign the modules as"
+			ewarn "described on the wiki [1]"
+			ewarn
+			ewarn "Consider using the MODULES_SIGN_KEY variable to use an 
external key."
+			ewarn
+			ewarn "[1]: https://wiki.gentoo.org/wiki/Signed_kernel_module_support"
+		fi
+	fi
  }

  # @FUNCTION: kernel-build_merge_configs
@@ -290,16 +355,39 @@ kernel-build_merge_configs() {
  	local user_configs=( "${BROOT}"/etc/kernel/config.d/*.config )
  	shopt -u nullglob

+	local merge_configs=( "${@}" )
+
+	if [[ ${KERNEL_IUSE_MODULES_SIGN} ]]; then
+		if use modules-sign; then
+			: "${MODULES_SIGN_HASH:=sha512}"
+			cat <<-EOF > "${WORKDIR}/modules-sign.config" || die
+				## Enable module signing
+				CONFIG_MODULE_SIG=y
+				CONFIG_MODULE_SIG_ALL=y
+				CONFIG_MODULE_SIG_FORCE=y
+				CONFIG_MODULE_SIG_${MODULES_SIGN_HASH^^}=y
+			EOF
+			if [[ ${MODULES_SIGN_KEY} == pkcs11:* || -e ${MODULES_SIGN_KEY} ]]; then
+				echo "CONFIG_MODULE_SIG_KEY=\"${MODULES_SIGN_KEY}\"" \
+					>> "${WORKDIR}/modules-sign.config"
+			elif [[ -n ${MODULES_SIGN_KEY} ]]; then
+				die "MODULES_SIGN_KEY=${MODULES_SIGN_KEY} not found!"
+			fi
+			merge_configs+=( "${WORKDIR}/modules-sign.config" )
+		fi
+	fi
+
  	if [[ ${#user_configs[@]} -gt 0 ]]; then
  		elog "User config files are being applied:"
  		local x
  		for x in "${user_configs[@]}"; do
  			elog "- ${x}"
  		done
+		merge_configs+=( "${user_configs[@]}" )
  	fi

  	./scripts/kconfig/merge_config.sh -m -r \
-		.config "${@}" "${user_configs[@]}" || die
+		.config "${merge_configs[@]}"  || die
  }

  fi