linux-kernel - [PATCH v1] sefltest/ima: support appended signatures (modsig)

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Message-Id: <1567005240-12912-1-git-send-email-zohar@linux.ibm.com>
Date:   Wed, 28 Aug 2019 11:14:00 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     linux-integrity@...r.kernel.org
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Petr Vorel <pvorel@...e.cz>, Jessica Yu <jeyu@...nel.org>,
        Dave Young <dyoung@...hat.com>, shuah <shuah@...nel.org>,
        linux-kselftest@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v1] sefltest/ima: support appended signatures (modsig)

In addition to the PE/COFF and IMA xattr signatures, the kexec kernel
image can be signed with an appended signature, using the same
scripts/sign-file tool that is used to sign kernel modules.

This patch adds support for detecting a kernel image signed with an
appended signature and updates the existing test messages
appropriately.

Reviewed-by: Petr Vorel <pvorel@...e.cz>
Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
---
 .../selftests/kexec/test_kexec_file_load.sh        | 38 +++++++++++++++++++---
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/kexec/test_kexec_file_load.sh b/tools/testing/selftests/kexec/test_kexec_file_load.sh
index fa7c24e8eefb..2ff600388c30 100755
--- a/tools/testing/selftests/kexec/test_kexec_file_load.sh
+++ b/tools/testing/selftests/kexec/test_kexec_file_load.sh
@@ -37,11 +37,20 @@ is_ima_sig_required()
 	# sequentially.  As a result, a policy rule may be defined, but
 	# might not necessarily be used.  This test assumes if a policy
 	# rule is specified, that is the intent.
+
+	# First check for appended signature (modsig), then xattr
 	if [ $ima_read_policy -eq 1 ]; then
 		check_ima_policy "appraise" "func=KEXEC_KERNEL_CHECK" \
-			"appraise_type=imasig"
+			"appraise_type=imasig|modsig"
 		ret=$?
-		[ $ret -eq 1 ] && log_info "IMA signature required";
+		if [ $ret -eq 1 ]; then
+			log_info "IMA or appended(modsig) signature required"
+		else
+			check_ima_policy "appraise" "func=KEXEC_KERNEL_CHECK" \
+				"appraise_type=imasig"
+			ret=$?
+			[ $ret -eq 1 ] && log_info "IMA signature required";
+		fi
 	fi
 	return $ret
 }
@@ -84,6 +93,22 @@ check_for_imasig()
 	return $ret
 }
 
+# Return 1 for appended signature (modsig) found and 0 for not found.
+check_for_modsig()
+{
+	local module_sig_string="~Module signature appended~"
+	local sig="$(tail --bytes $((${#module_sig_string} + 1)) $KERNEL_IMAGE)"
+	local ret=0
+
+	if [ "$sig" == "$module_sig_string" ]; then
+		ret=1
+		log_info "kexec kernel image modsig signed"
+	else
+		log_info "kexec kernel image not modsig signed"
+	fi
+	return $ret
+}
+
 kexec_file_load_test()
 {
 	local succeed_msg="kexec_file_load succeeded"
@@ -98,7 +123,8 @@ kexec_file_load_test()
 		# In secureboot mode with an architecture  specific
 		# policy, make sure either an IMA or PE signature exists.
 		if [ $secureboot -eq 1 ] && [ $arch_policy -eq 1 ] && \
-			[ $ima_signed -eq 0 ] && [ $pe_signed -eq 0 ]; then
+			[ $ima_signed -eq 0 ] && [ $pe_signed -eq 0 ] \
+			  && [ $ima_modsig -eq 0 ]; then
 			log_fail "$succeed_msg (missing sig)"
 		fi
 
@@ -107,7 +133,8 @@ kexec_file_load_test()
 			log_fail "$succeed_msg (missing PE sig)"
 		fi
 
-		if [ $ima_sig_required -eq 1 ] && [ $ima_signed -eq 0 ]; then
+		if [ $ima_sig_required -eq 1 ] && [ $ima_signed -eq 0 ] \
+		     && [ $ima_modsig -eq 0 ]; then
 			log_fail "$succeed_msg (missing IMA sig)"
 		fi
 
@@ -204,5 +231,8 @@ pe_signed=$?
 check_for_imasig
 ima_signed=$?
 
+check_for_modsig
+ima_modsig=$?
+
 # Test loading the kernel image via kexec_file_load syscall
 kexec_file_load_test
-- 
2.7.5