LUKS header change validation at both sealing and unsealing of TPM Disk Unlock Key.

Fixes linuxboot#1092.
Supersedes linuxboot#1093

- Cherry-picks ed1c23a (credit to @hardened-vault) thank you!)
- Addresses and correct self-review under linuxboot#1093 (@hardened-vault: you don't answer often here!)
  - kexec-unseal-key: Warn a user who attempts to default boot while his Disk Unlock Key passphrase fails to unseal because LUKS headers changed.
    (linuxboot#1093 (comment))
  - kexec-seal-key: Identical as in ed1c23a
  - kexec-add-key: Tell the user that the Headers did not change when changing TPM released Disk Unlock Key
    (Through changing default boot at Options->Boot Options -> Show OS boot options: select a new boot option
    and set a Disk Unlock Key in TPM, accept to modify disk and sign /boot options)
    - Here, we cancel the diff output shown on screen linuxboot#1093 (comment)
    - And we change the warning given to the user to past tense "Headers of LUKS containers to be unlocked via TPM Disk Unlock Key passphrase did not change."

Signed-off-by: Thierry Laurion <insurgo@riseup.net>

Author: tlaurion

initrd/bin/kexec-insert-key

@@ -57,6 +57,9 @@ tpmr extend -ix 4 -ic generic ||
 # Check to continue
 if [ "$unseal_failed" = "y" ]; then
 	confirm_boot="n"
+	if diff "$(dirname $INITRD)/kexec_lukshdr_hash.txt" /tmp/luksDump.txt > /dev/null 2>&1; then
+		echo "Headers of LUKS containers to be unlocked via TPM Disk Unlock Key passphrase did not change."
+	fi
 	read \
 		-n 1 \
 		-p "Do you wish to boot and use the LUKS Disk Recovery Key? [Y/n] " \

initrd/bin/kexec-unseal-key

@@ -40,6 +40,14 @@ for tries in 1 2 3; do
 
 	DEBUG $(pcrs)
 	warn "Unable to unseal disk encryption key"
+	if [ -e /boot/kexec_lukshdr_hash.txt -a -e /tmp/luksDump.txt ]; then
+		if ! diff /boot/kexec_lukshdr_hash.txt /tmp/luksDump.txt > /dev/null 2>&1; then
+			warn "Encrypted LUKS(es) container(s) headers changed since they were measured and sealed in TPM for Disk Unlock key. You might want to investigate."
+		fi
+	else
+		warn "No encrypted LUKS container(s) headers were found/comparable under /boot/kexec_lukshdr_hash.txt"
+		warn "You might need to setup a new boot default and Disk Unlock Key from Options->Boot Options->Show OS boot menu."
+	fi
 done
 
 die "Retry count exceeded..."