Merge ~ubuntu-core-dev/grub/+git/ubuntu:check-known-sigs into ~ubuntu-core-dev/grub/+git/ubuntu:ubuntu

[Mathieu Trudel-Lapierre]

grub-check-signatures: check kernel signatures against known certs from firmware

Check kernel signatures against the certs we can export from firmware, and against the Canonical cert we can ship on disk (to guard against an empty MokListRT, despite the cert really being known by our shim).

I think the low risk of false positives (saying we trust the Canonical signature when people use their own shim, etc.) is low enough, and it's an unlikely setup already, that people can deal with it on their own.

[Steve Langasek (vorlon)]

review: Needs Fixing

diff --git a/debian/canonical-uefi-ca.crt b/debian/canonical-uefi-ca.crt
new file mode 100644
index 0000000..55c06d5
--- /dev/null
+++ b/debian/canonical-uefi-ca.crt
@@ -0,0 +1,25 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
diff --git a/debian/grub-check-signatures b/debian/grub-check-signatures
index 1c486a1..1daf589 100755
--- a/debian/grub-check-signatures
+++ b/debian/grub-check-signatures
@@ -8,6 +8,7 @@ set -e
 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.
@@ -38,13 +39,44 @@ on_secure_boot() {
 	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; \
+		mokutil --export --mok >/dev/null 2>/dev/null; \
+		for derfile in *.der; do \
+			openssl x509 -inform der -in $derfile -outform pem -out $derfile.crt; \
+		done )
+}
+
 # Check if a given kernel image is signed
 is_signed() {
 	tmp=$(mktemp)
-	sbattach --detach $tmp $1 >/dev/null  	# that's ugly...
+	sbattach --detach $tmp $1 >/dev/null 2>/dev/null 	# that's ugly...
 	test "$(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 $1 >/dev/null 2>/dev/null
+			result=$?
+			if [ $result -eq 0 ]; then
+				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
 	return $result
 }
 
@@ -71,7 +103,7 @@ find_unsigned() {
 
 # Only reached from show_warning
 error() {
-	echo "E: Your kernels are unsigned. This system will fail to boot in a secure boot environment." >&2
+	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
 }
 
@@ -90,8 +122,10 @@ show_warning() {
 }
 
 if on_secure_boot; then
+	extract_known_keys
 	unsigned="$(find_unsigned)"
 	if [ -n "$unsigned" ]; then
 		show_warning "$unsigned"
 	fi
+	rm -rf "$tmpdir"
 fi
diff --git a/debian/grub-common.install.in b/debian/grub-common.install.in
index 0a562a6..8e31573 100644
--- a/debian/grub-common.install.in
+++ b/debian/grub-common.install.in
@@ -1,6 +1,7 @@
 ../../debian/apport/source_grub2.py	usr/share/apport/package-hooks/
 ../../debian/grub.d			etc
 ../../debian/grub-check-signatures usr/share/grub/
+../../debian/canonical-uefi-ca.crt usr/share/grub/
 
 etc/bash_completion.d
 etc/grub.d