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grub-check-signatures
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#!/bin/sh set -e . /usr/share/debconf/confmodule # Check if we are on an EFI system efivars=/sys/firmware/efi/efivars secureboot_var=SecureBoot-8be4df61-93ca-11d2-aa0d-00e098032b8c moksbstatert_var=MokSBStateRT-605dab50-e046-4300-abb6-3dd810dd8b23 tmpdir=$(mktemp -d) on_secure_boot() { # Validate any queued actions before we go try to do them. local moksbstatert=0 if ! [ -d $efivars ]; then return 1 fi if ! [ -f $efivars/$secureboot_var ] \ || [ "$(od -An -t u1 $efivars/$secureboot_var | awk '{ print $NF }')" -ne 1 ] then return 1 fi if [ -f /proc/sys/kernel/moksbstate_disabled ]; then moksbstatert=$(cat /proc/sys/kernel/moksbstate_disabled 2>/dev/null || echo 0) elif [ -f $efivars/$moksbstatert_var ]; then # MokSBStateRT set to 1 means validation is disabled moksbstatert=$(od -An -t u1 $efivars/$moksbstatert_var | \ awk '{ print $NF; }') fi if [ $moksbstatert -eq 1 ]; then return 1 fi return 0 } # Retrieve the keys we do trust from PK, DB, KEK, and MokList. extract_known_keys() { # Make the Canonical CA cert available for validation too; in case # MokListRT is empty due to a bug. cp /usr/share/grub/canonical-uefi-ca.crt $tmpdir # Extract known UEFI certs from firmware variables ( cd $tmpdir; \ mokutil --export --db >/dev/null 2>/dev/null; \ mokutil --export --mok >/dev/null 2>/dev/null; ) find $tmpdir -name "*.der" -exec openssl x509 -inform der -in {} -outform pem -out {}.crt \; } # Check if a given kernel image is signed is_signed() { kernel=$1 tmp=$(mktemp) kernel_tmp=$(mktemp) if zcat $kernel > $kernel_tmp 2>/dev/null; then kernel=$kernel_tmp fi sbattach --detach $tmp $kernel >/dev/null 2>/dev/null # that's ugly... test "$(wc -c < $tmp)" -ge 16 # Just _some_ minimum size result=$? if [ $result -eq 0 ]; then sig_subject=$(openssl pkcs7 -inform der -in $tmp -print_certs | openssl x509 -noout -text | grep Subject: ) fi rm $tmp if [ $result -eq 0 ]; then for crtfile in $tmpdir/*.crt; do sbverify --cert $crtfile $kernel >/dev/null 2>/dev/null result=$? if [ $result -eq 0 ]; then rm "$kernel_tmp" return $result; fi done echo "$1 is signed, but using an unknown key:" >&2 echo "$sig_subject" >&2 else echo "$1 is unsigned." >&2 fi rm "$kernel_tmp" return $result } # Check that our current kernel and every newer one is signed find_unsigned() { uname_r="$(uname -r)" for kernel in $(ls -1 /boot/vmlinuz-* | sort -V -r); do # no kernels :( if [ "$kernel" = "/boot/vmlinuz-*" ]; then break fi this_uname_r="$(echo "$kernel" | sed -r 's#^/boot/vmlinuz-(.*)#\1#; s#\.efi\.signed$##')" if dpkg --compare-versions "$this_uname_r" lt "$uname_r"; then continue fi if [ -e "$kernel.efi.signed" ]; then continue fi if ! is_signed $kernel; then echo "$this_uname_r" fi done } # Only reached from show_warning error() { echo "E: Your kernels are not signed with a key known to your firmware. This system will fail to boot in a Secure Boot environment." >&2 exit 1 } # Either shows a debconf note or prints an error with error() above if # that fails show_warning() { # kernels should be an indented list of one version per line escaped="$(printf "%s" "$unsigned" | sed "s#^# #" | debconf-escape -e )" db_capb escape db_settitle grub2/unsigned_kernels_title || error db_fset grub2/unsigned_kernels seen 0 || error db_subst grub2/unsigned_kernels unsigned_versions "$escaped" || error db_input critical grub2/unsigned_kernels || error db_go || error error } if on_secure_boot; then extract_known_keys unsigned="$(find_unsigned)" if [ -n "$unsigned" ]; then show_warning "$unsigned" fi rm -rf "$tmpdir" fi