linux-kernel - [PATCH v2] powerpc/ima: fix secure boot rules in ima arch policy

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Date:   Fri,  1 May 2020 10:16:52 -0400
From:   Nayna Jain <nayna@...ux.ibm.com>
To:     linux-integrity@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, Mimi Zohar <zohar@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nayna Jain <nayna@...ux.ibm.com>
Subject: [PATCH v2] powerpc/ima: fix secure boot rules in ima arch policy

To prevent verifying the kernel module appended signature twice
(finit_module), once by the module_sig_check() and again by IMA, powerpc
secure boot rules define an IMA architecture specific policy rule
only if CONFIG_MODULE_SIG_FORCE is not enabled. This, unfortunately, does
not take into account the ability of enabling "sig_enforce" on the boot
command line (module.sig_enforce=1).

Including the IMA module appraise rule results in failing the finit_module
syscall, unless the module signing public key is loaded onto the IMA
keyring.

This patch fixes secure boot policy rules to be based on CONFIG_MODULE_SIG
instead.

Fixes: 4238fad366a6 ("powerpc/ima: Add support to initialize ima policy rules")
Signed-off-by: Nayna Jain <nayna@...ux.ibm.com>
---
v2:
* Fixes the patch description to specify the problem more clearly as asked 
by Michael Ellerman.

 arch/powerpc/kernel/ima_arch.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/ima_arch.c b/arch/powerpc/kernel/ima_arch.c
index e34116255ced..957abd592075 100644
--- a/arch/powerpc/kernel/ima_arch.c
+++ b/arch/powerpc/kernel/ima_arch.c
@@ -19,12 +19,12 @@ bool arch_ima_get_secureboot(void)
  * to be stored as an xattr or as an appended signature.
  *
  * To avoid duplicate signature verification as much as possible, the IMA
- * policy rule for module appraisal is added only if CONFIG_MODULE_SIG_FORCE
+ * policy rule for module appraisal is added only if CONFIG_MODULE_SIG
  * is not enabled.
  */
 static const char *const secure_rules[] = {
 	"appraise func=KEXEC_KERNEL_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
-#ifndef CONFIG_MODULE_SIG_FORCE
+#ifndef CONFIG_MODULE_SIG
 	"appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
 #endif
 	NULL
@@ -50,7 +50,7 @@ static const char *const secure_and_trusted_rules[] = {
 	"measure func=KEXEC_KERNEL_CHECK template=ima-modsig",
 	"measure func=MODULE_CHECK template=ima-modsig",
 	"appraise func=KEXEC_KERNEL_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
-#ifndef CONFIG_MODULE_SIG_FORCE
+#ifndef CONFIG_MODULE_SIG
 	"appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
 #endif
 	NULL
-- 
2.18.1