linux-kernel - [PATCH v6] ima: move APPRAISE_BOOTPARAM dependency on ARCH

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Date:   Mon, 13 Jul 2020 13:48:30 -0300
From:   Bruno Meneguele <bmeneg@...hat.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-integrity@...r.kernel.org
Cc:     zohar@...ux.ibm.com, erichte@...ux.ibm.com, nayna@...ux.ibm.com,
        stable@...r.kernel.org, Bruno Meneguele <bmeneg@...hat.com>
Subject: [PATCH v6] ima: move APPRAISE_BOOTPARAM dependency on ARCH_POLICY to runtime

The IMA_APPRAISE_BOOTPARAM config allows enabling different "ima_appraise="
modes - log, fix, enforce - at run time, but not when IMA architecture
specific policies are enabled.  This prevents properly labeling the
filesystem on systems where secure boot is supported, but not enabled on the
platform.  Only when secure boot is actually enabled should these IMA
appraise modes be disabled.

This patch removes the compile time dependency and makes it a runtime
decision, based on the secure boot state of that platform.

Test results as follows:

-> x86-64 with secure boot enabled

[    0.015637] Kernel command line: <...> ima_policy=appraise_tcb ima_appraise=fix
[    0.015668] ima: Secure boot enabled: ignoring ima_appraise=fix boot parameter option

-> powerpc with secure boot disabled

[    0.000000] Kernel command line: <...> ima_policy=appraise_tcb ima_appraise=fix
[    0.000000] Secure boot mode disabled

-> Running the system without secure boot and with both options set:

CONFIG_IMA_APPRAISE_BOOTPARAM=y
CONFIG_IMA_ARCH_POLICY=y

Audit prompts "missing-hash" but still allow execution and, consequently,
filesystem labeling:

type=INTEGRITY_DATA msg=audit(07/09/2020 12:30:27.778:1691) : pid=4976
uid=root auid=root ses=2
subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 op=appraise_data
cause=missing-hash comm=bash name=/usr/bin/evmctl dev="dm-0" ino=493150
res=no

Cc: stable@...r.kernel.org
Fixes: d958083a8f64 ("x86/ima: define arch_get_ima_policy() for x86")
Signed-off-by: Bruno Meneguele <bmeneg@...hat.com>
---
v6:
  - explictly print the bootparam being ignored to the user (Mimi)
v5:
  - add pr_info() to inform user the ima_appraise= boot param is being
	ignored due to secure boot enabled (Nayna)
  - add some testing results to commit log
v4:
  - instead of change arch_policy loading code, check secure boot state at
	"ima_appraise=" parameter handler (Mimi)
v3:
  - extend secure boot arch checker to also consider trusted boot
  - enforce IMA appraisal when secure boot is effectively enabled (Nayna)
  - fix ima_appraise flag assignment by or'ing it (Mimi)
v2:
  - pr_info() message prefix correction
 security/integrity/ima/Kconfig        | 2 +-
 security/integrity/ima/ima_appraise.c | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index edde88dbe576..62dc11a5af01 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -232,7 +232,7 @@ config IMA_APPRAISE_REQUIRE_POLICY_SIGS
 
 config IMA_APPRAISE_BOOTPARAM
 	bool "ima_appraise boot parameter"
-	depends on IMA_APPRAISE && !IMA_ARCH_POLICY
+	depends on IMA_APPRAISE
 	default y
 	help
 	  This option enables the different "ima_appraise=" modes
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index a9649b04b9f1..28a59508c6bd 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -19,6 +19,12 @@
 static int __init default_appraise_setup(char *str)
 {
 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
+	if (arch_ima_get_secureboot()) {
+		pr_info("Secure boot enabled: ignoring ima_appraise=%s boot parameter option",
+			str);
+		return 1;
+	}
+
 	if (strncmp(str, "off", 3) == 0)
 		ima_appraise = 0;
 	else if (strncmp(str, "log", 3) == 0)
-- 
2.26.2