Re: [PATCH v5] ima: move APPRAISE_BOOTPARAM dependency on ARCH_POLICY to runtime

On Fri, Jul 10, 2020 at 02:54:48PM -0400, Mimi Zohar wrote:

On Fri, 2020-07-10 at 15:34 -0300, Bruno Meneguele wrote:

quoted

On Fri, Jul 10, 2020 at 03:03:38PM -0300, Bruno Meneguele wrote:

quoted

On Fri, Jul 10, 2020 at 01:23:24PM -0400, Mimi Zohar wrote:

quoted

On Thu, 2020-07-09 at 13:46 -0300, Bruno Meneguele wrote:

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APPRAISE_BOOTPARAM has been marked as dependent on !ARCH_POLICY in compile
time, enforcing the appraisal whenever the kernel had the arch policy option
enabled.

quoted

However it breaks systems where the option is set but the system didn't
boot in a "secure boot" platform. In this scenario, anytime an appraisal
policy (i.e. ima_policy=appraisal_tcb) is used it will be forced, without
giving the user the opportunity to label the filesystem, before enforcing
integrity.

Considering the ARCH_POLICY is only effective when secure boot is actually
enabled this patch remove the compile time dependency and move it to a
runtime decision, based on the secure boot state of that platform.

Perhaps we could simplify this patch description a bit?

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
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.

Sounds good to me.

quoted

<snip>

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diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index a9649b04b9f1..884de471b38a 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c

@@ -19,6 +19,11 @@
 static int __init default_appraise_setup(c

quoted

har *str)
 {
 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
+	if (arch_ima_get_secureboot()) {
+		pr_info("appraise boot param ignored: secure boot enabled");

Instead of a generic statement, is it possible to include the actual
option being denied?  Perhaps something like: "Secure boot enabled,
ignoring %s boot command line option"

Mimi

Yes, sure.

Btw, would it make sense to first make sure we have a valid "str"
option and not something random to print?
 

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index a9649b04b9f1..1f1175531d3e 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c

@@ -25,6 +25,16 @@ static int __init default_appraise_setup(char *str)
                ima_appraise = IMA_APPRAISE_LOG;
        else if (strncmp(str, "fix", 3) == 0)
                ima_appraise = IMA_APPRAISE_FIX;
+       else
+               pr_info("invalid \"%s\" appraise option");
+
+       if (arch_ima_get_secureboot()) {
+               if (!is_ima_appraise_enabled()) {
+                       pr_info("Secure boot enabled: ignoring ima_appraise=%s boot parameter option",
+                               str);
+                       ima_appraise = IMA_APPRAISE_ENFORCE;
+               }
+       }

Providing feedback is probably a good idea.  However, the
"arch_ima_get_secureboot" test can't come after setting
"ima_appraise."

Sorry, but I'm not sure if I got the reason to why it can't be done
after: would it be basically to prevent any further processing about
ima_appraise as a matter of security principle? Or maybe to keep the
dependency between secureboot and bootparam truly strict? 

Or are there something else I'm missing?

Mimi

quoted

 #endif
        return 1;
 }


The "else" there I think would make sense as well, at least to give the
user some feedback about a possible mispelling of him (as a separate
patch).

And "if(!is_ima_appraise_enabled())" would avoid to print anything about
"ignoring the option" to the user in case he explicitly set "enforce",
which we know there isn't any real effect but is allowed and shown in
kernel-parameters.txt.

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Thanks!

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+		return 1;
+	}
+
 	if (strncmp(str, "off", 3) == 0)
 		ima_appraise = 0;
 	else if (strncmp(str, "log", 3) == 0)

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