Merge ~juliank/shim/+git/shim-signed:alternatives into ~ubuntu-core-dev/shim/+git/shim-signed:master

[Julian Andres Klode]

A way to ease the pain of key rotation using alternatives

[Julian Andres Klode (juliank)]

on_secure_boot and most of have_non_revoked_kernel are copied from grub-check-signatures (which would fail postinst with a debconf dialog, which is not actually meaningful as the files are unpacked and would be used). We should evaluate unifying things in the future, but this avoids both tying in a grub2 SRU (there is one in progress already) and our is-not-revoked helper can be used for build-time testing.

[Julian Andres Klode (juliank)]

I need to actually copy in the bugs closed to the changelog but the implementation is ready for reviews now.

be6be0f... by Julian Andres Klode on 2023-01-26

Release 1.52~ppa7

[Julian Andres Klode (juliank)]

Regarding the design decisions, please see the ubuntu-devel thread. I think most of the complexity is in actually checking if we are good to install, so this is not a lot more complex than aborting in preinst but means it works fine if kernels and shim are upgraded in the same upgrade run, like setup_alternatives + hooking it into the kernel postinst.d is less code than putting up a debconf dialog with an error message :)

In a month or so, when we're sure everyone has upgraded their kernel we could remove the alternatives again and abort in preinst so that people can find out more easily that they're actually using shim 15.7 and not the old version.

[Steve Langasek (vorlon)]

review: Needs Fixing

[Steve Langasek (vorlon)]

review: Approve

Unmerged commits

be6be0f... by Julian Andres Klode on 2023-01-26

Release 1.52~ppa7

diff --git a/Makefile b/Makefile
index 5c24871..aab638f 100644
--- a/Makefile
+++ b/Makefile
@@ -14,8 +14,9 @@ all:
 	sbattach --attach external-$(EFI_ARCH_LOWER).p7c $(SHIM_VERSION)/$(SHIM_BASE).signed
 
 	# Copy external & dualsigned shims
-	cp $(SHIM_VERSION)/$(SHIM_BASE) build/$(SHIM_BASE).signed
+	cp $(SHIM_VERSION)/$(SHIM_BASE) build/$(SHIM_BASE).signed.latest
 	cp $(SHIM_VERSION)/$(SHIM_BASE).signed build/$(SHIM_BASE).dualsigned
+	cp external-shim$(EFI_ARCH_LOWER).efi.previous build/$(SHIM_BASE).signed.previous
 
 	# Move archive signed fb*.efi & mm*.efi
 	mv $(SHIM_VERSION)/$(FB_BASE).signed build/$(FB_BASE)
@@ -26,13 +27,16 @@ all:
 
 check:
 	# Verify all signatures
-	sbverify --verbose --cert external.pem build/$(SHIM_BASE).signed
+	sbverify --verbose --cert external.pem build/$(SHIM_BASE).signed.latest
+	sbverify --verbose --cert external.pem build/$(SHIM_BASE).signed.previous
 	sbverify --verbose --cert external.pem build/$(SHIM_BASE).dualsigned
 	sbverify --verbose --cert $(SHIM_VERSION)/control/uefi.crt build/$(SHIM_BASE).dualsigned
 	sbverify --verbose --cert $(SHIM_VERSION)/control/uefi.crt build/$(FB_BASE)
 	sbverify --verbose --cert $(SHIM_VERSION)/control/uefi.crt build/$(MM_BASE)
 	# verify sbattach binary output matches the externally-signed binary
-	cmp external-shim$(EFI_ARCH_LOWER).efi build/$(SHIM_BASE).signed
+	cmp external-shim$(EFI_ARCH_LOWER).efi build/$(SHIM_BASE).signed.latest
+	# Check that we are not signed with revoked keys
+	./is-not-revoked  build/$(FB_BASE) build/$(MM_BASE) build/$(SHIM_BASE).dualsigned
 
 clean:
 	rm -rf build $(SHIM_VERSION) external-$(EFI_ARCH_LOWER).p7c
diff --git a/debian/changelog b/debian/changelog
index 1b31422..abed987 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,21 @@
+shim-signed (1.52~ppa7) kinetic; urgency=medium
+
+  * New upstream version 15.7 (LP: #1996503)
+    - SBAT level: shim,3
+    - SBAT policy bumped to for grub,2 in previous and grub,3 in latest:
+      SBAT policy: latest="shim,2\ngrub,3\n" previous="grub,2\n"
+  * SECURITY FIX: Buffer overflow when loading crafted EFI images.
+      - CVE-2022-28737
+  * debian/control: Depend on new grub versions (1.191 on lunar+, 1.187.2 elsewhere)
+  * Break fwupd-signed signed with old keys
+  * Check for revoked fb,mm binaries in build, grubs, fwupd in autopkgtest
+  * Install both previous and latest shim as alternatives. On secure boot
+    systems, if the current kernel or any newer one is revoked, the previous
+    shim will continue to be used until current kernel and all newer ones
+    are signed with a non-revoked key.
+
+ -- Julian Andres Klode <[e-mail]>  Thu, 26 Jan 2023 13:03:25 +0100
+
 shim-signed (1.51) impish; urgency=medium
 
   * Update to shim 15.4-0ubuntu9
diff --git a/debian/control b/debian/control
index 1ecec76..ae3c7b7 100644
--- a/debian/control
+++ b/debian/control
@@ -9,8 +9,8 @@ Vcs-Browser: https://git.launchpad.net/~ubuntu-core-dev/shim/+git/shim-signed
 
 Package: shim-signed
 Architecture: amd64 arm64
-Depends: ${misc:Depends}, grub-efi-amd64-signed | grub-efi-arm64-signed, grub2-common (>= 2.04-1ubuntu24), mokutil (>= 0.3.0+1538710437.fb6250f-0ubuntu2), sbsigntool
-Breaks: shim (<< 15.3)
+Depends: ${misc:Depends}, grub-efi-amd64-signed (>= 1.191~) | grub-efi-arm64-signed (>= 1.191~) | base-files (<< 12.3), grub-efi-amd64-signed (>= 1.187.2~) | grub-efi-arm64-signed (>= 1.187.2~), grub2-common (>= 2.04-1ubuntu24), mokutil (>= 0.3.0+1538710437.fb6250f-0ubuntu2), sbsigntool
+Breaks: shim (<< 15.3), fwupd-signed (<< 1.44.1~)
 Replaces: shim (<< 15.3)
 Recommends: secureboot-db
 Built-Using: shim (= ${shim:Version})
diff --git a/debian/kernel-postinst.d/zz-shim b/debian/kernel-postinst.d/zz-shim
new file mode 100755
index 0000000..93a41e6
--- /dev/null
+++ b/debian/kernel-postinst.d/zz-shim
@@ -0,0 +1,6 @@
+#!/bin/sh
+# Try to update shim alternative if pointing to previous shim
+if update-alternatives --query shimx64.efi.signed | grep "Best: /usr/lib/shim/shimx64.efi.signed.previous" -q; then
+	dpkg-trigger shim-kernel-check
+fi
+
diff --git a/debian/shim-signed.install b/debian/shim-signed.install
index 6037db5..c6179e9 100755
--- a/debian/shim-signed.install
+++ b/debian/shim-signed.install
@@ -4,8 +4,11 @@ build/${SHIM_BASE} /usr/lib/shim
 build/${FB_BASE} /usr/lib/shim
 build/${MM_BASE} /usr/lib/shim
 build/BOOT${EFI_ARCH}.CSV /usr/lib/shim
-build/${SHIM_BASE}.signed /usr/lib/shim
+build/${SHIM_BASE}.signed.latest /usr/lib/shim
+build/${SHIM_BASE}.signed.previous /usr/lib/shim
 build/${SHIM_BASE}.dualsigned /usr/lib/shim
 openssl.cnf /usr/lib/shim/mok
 debian/source_shim-signed.py /usr/share/apport/package-hooks/
+debian/kernel-postinst.d/zz-shim /etc/kernel/postinst.d/
 update-secureboot-policy /usr/sbin/
+is-not-revoked /usr/lib/shim
diff --git a/debian/shim-signed.postinst b/debian/shim-signed.postinst
old mode 100644
new mode 100755
index ebc0c42..497ba66
--- a/debian/shim-signed.postinst
+++ b/debian/shim-signed.postinst
@@ -4,6 +4,75 @@ set -e
 # Must load the confmodule for our template to be installed correctly.
 . /usr/share/debconf/confmodule
 
+efivars=/sys/firmware/efi/efivars
+secureboot_var=SecureBoot-8be4df61-93ca-11d2-aa0d-00e098032b8c
+moksbstatert_var=MokSBStateRT-605dab50-e046-4300-abb6-3dd810dd8b23
+
+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 [ $moksbstatert -eq 1 ]; then
+		return 1
+	fi
+
+	return 0
+}
+
+# Check that our current kernel and every newer one has not been revoked
+find_revoked() {
+	uname_r="$(uname -r)"
+	exit=1
+	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 ! /usr/lib/shim/is-not-revoked "$kernel"; then
+			exit=0
+		fi
+	done
+	return $exit
+}
+
+setup_alternatives() {
+	for efi_arch in x64 aa64; do
+		test -e /usr/lib/shim/shim${efi_arch}.efi.signed.latest || continue
+		if ! on_secure_boot || ! find_revoked; then
+			update-alternatives --install /usr/lib/shim/shim${efi_arch}.efi.signed shimx64.efi.signed /usr/lib/shim/shim${efi_arch}.efi.signed.latest 100
+			update-alternatives --install /usr/lib/shim/shim${efi_arch}.efi.signed shimx64.efi.signed /usr/lib/shim/shim${efi_arch}.efi.signed.previous 50
+		else
+			update-alternatives --install /usr/lib/shim/shim${efi_arch}.efi.signed shimx64.efi.signed /usr/lib/shim/shim${efi_arch}.efi.signed.latest 50
+			update-alternatives --install /usr/lib/shim/shim${efi_arch}.efi.signed shimx64.efi.signed /usr/lib/shim/shim${efi_arch}.efi.signed.previous 100
+		fi
+	done
+}
+
 config_item ()
 {
     if [ -f /etc/default/grub ]; then
@@ -54,13 +123,32 @@ case $(dpkg --print-architecture) in
 	grubarch=arm64-efi
 	;;
 esac
-case $1 in
-    triggered)
+case "$1:$2" in
+    triggered:shim-secureboot-policy)
 	if [ -e /var/lib/shim-signed/mok/MOK.priv ]; then
 	    SHIM_NOTRIGGER=y update-secureboot-policy --enroll-key
 	fi
 	;;
-    configure)
+    triggered:shim-kernel-check)
+	setup_alternatives
+	# If we did not switch to the latest shim, do not reinstall shim and grub.
+	if update-alternatives --query shimx64.efi.signed | grep "Best: /usr/lib/shim/shimx64.efi.signed.previous" -q; then
+		exit 0
+	fi
+	bootloader_id="$(config_item GRUB_DISTRIBUTOR | tr A-Z a-z | \
+			 cut -d' ' -f1)"
+	case $bootloader_id in
+	    kubuntu) bootloader_id=ubuntu ;;
+	esac
+	# Check /boot/grub to see if we previously installed to an ESP. We don't
+	# want to trigger the install code just by installing the package,
+	# normally the installer installs grub itself first.
+	if [ -e /boot/grub/${grubarch}/core.efi ]; then
+	    /usr/lib/grub/grub-multi-install --target=${grubarch} --auto-nvram
+	fi
+    ;;
+    configure:*)
+	setup_alternatives
 	bootloader_id="$(config_item GRUB_DISTRIBUTOR | tr A-Z a-z | \
 			 cut -d' ' -f1)"
 	case $bootloader_id in
diff --git a/debian/shim-signed.triggers b/debian/shim-signed.triggers
index 2b33128..e3c63ad 100644
--- a/debian/shim-signed.triggers
+++ b/debian/shim-signed.triggers
@@ -1 +1,2 @@
 interest-noawait shim-secureboot-policy
+interest-noawait shim-kernel-check
diff --git a/debian/tests/control b/debian/tests/control
new file mode 100644
index 0000000..b3525ab
--- /dev/null
+++ b/debian/tests/control
@@ -0,0 +1,3 @@
+Tests: test-is-not-revoked
+Restrictions: allow-stderr, needs-root
+Depends: shim-signed, grub-efi-amd64-signed | grub-efi-arm64-signed, fwupd-signed, sbsigntool
diff --git a/debian/tests/test-is-not-revoked b/debian/tests/test-is-not-revoked
new file mode 100755
index 0000000..2ab4e63
--- /dev/null
+++ b/debian/tests/test-is-not-revoked
@@ -0,0 +1,6 @@
+#!/bin/sh
+exec /usr/lib/shim/is-not-revoked \
+    /usr/lib/grub/*-signed/*.signed \
+    /usr/libexec/fwupd/efi/*.efi.signed \
+    /usr/lib/shim/fb*.efi \
+    /usr/lib/shim/mm*.efi
diff --git a/external-shimaa64.efi.previous b/external-shimaa64.efi.previous
new file mode 120000
index 0000000..d1dae88
--- /dev/null
+++ b/external-shimaa64.efi.previous
@@ -0,0 +1 @@
+microsoft-shimaa64.efi.previous
\ No newline at end of file
diff --git a/external-shimx64.efi.previous b/external-shimx64.efi.previous
new file mode 120000
index 0000000..3b6f052
--- /dev/null
+++ b/external-shimx64.efi.previous
@@ -0,0 +1 @@
+microsoft-shimx64.efi.previous
\ No newline at end of file
diff --git a/is-not-revoked b/is-not-revoked
new file mode 100755
index 0000000..1ed1423
--- /dev/null
+++ b/is-not-revoked
@@ -0,0 +1,50 @@
+#!/bin/bash
+set -e
+# we need to set lastpipe so we can read the signers into the signers array below
+shopt -s lastpipe
+
+exit=0
+
+quiet=""
+if [ "$1" = "-q" ]; then
+	quiet=true
+	shift
+fi
+
+for signed_binary in "$@"; do
+	if [ ! -e "$signed_binary" ]; then
+		echo "E: $signed_binary: file not found">&2
+		exit=1
+		continue
+	fi
+
+	sbverify --list "$signed_binary" | grep subject: | grep -E -o "CN=([^/]|\\/)*" | readarray -t signers
+	if [ -z "$signers" ]; then
+		echo "E: $signed_binary: Could not finder signing subject, sbverify output follows:">&2
+		sbverify --list "$signed_binary" >&2
+		exit=1
+		continue
+	fi
+
+	for signer in "${signers[@]}"; do
+		revoked=$(grep -xF "$signer" << EOF
+CN=Canonical Ltd. Secure Boot Signing
+CN=Canonical Ltd. Secure Boot Signing (2017)
+CN=Canonical Ltd. Secure Boot Signing (ESM 2018)
+CN=Canonical Ltd. Secure Boot Signing (2019)
+CN=Canonical Ltd. Secure Boot Signing (Ubuntu Core 2019)
+CN=Canonical Ltd. Secure Boot Signing (2021 v1)
+CN=Canonical Ltd. Secure Boot Signing (2021 v2)
+CN=Canonical Ltd. Secure Boot Signing (2021 v3)
+EOF
+	) || true
+
+		if [ "$revoked" ]; then
+			if [ -z "$quiet" ]; then
+				echo "E: $signed_binary: revoked key $revoked used">&2
+			fi
+			exit=1
+		fi
+    done
+done
+exit $exit
diff --git a/microsoft-shimaa64.efi b/microsoft-shimaa64.efi
index c1650a2..ca2da42 100644
Binary files a/microsoft-shimaa64.efi and b/microsoft-shimaa64.efi differ
diff --git a/microsoft-shimaa64.efi.previous b/microsoft-shimaa64.efi.previous
new file mode 100644
index 0000000..c1650a2
Binary files /dev/null and b/microsoft-shimaa64.efi.previous differ
diff --git a/microsoft-shimx64.efi b/microsoft-shimx64.efi
index e75c6cc..e18de43 100644
Binary files a/microsoft-shimx64.efi and b/microsoft-shimx64.efi differ
diff --git a/microsoft-shimx64.efi.previous b/microsoft-shimx64.efi.previous
new file mode 100644
index 0000000..e75c6cc
Binary files /dev/null and b/microsoft-shimx64.efi.previous differ