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Date: Thu, 27 Sep 2018 09:27:49 -0400
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Nayna Jain <nayna@...ux.vnet.ibm.com>,
linux-integrity@...r.kernel.org
Cc: linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org,
linux-kernel@...r.kernel.org, dhowells@...hat.com,
jforbes@...hat.com
Subject: Re: [PATCH v4 4/6] ima: add support for arch specific policies
On Wed, 2018-09-26 at 17:52 +0530, Nayna Jain wrote:
> Builtin IMA policies can be enabled on the boot command line, and replaced
> with a custom policy, normally during early boot in the initramfs. Build
> time IMA policy rules were recently added. These rules are automatically
> enabled on boot and persist after loading a custom policy.
>
> There is a need for yet another type of policy, an architecture specific
> policy, which is derived at runtime during kernel boot, based on the
> runtime secure boot flags. Like the build time policy rules, these rules
> persist after loading a custom policy.
>
> This patch adds support for loading an architecture specific IMA policy.
Thanks! Just a couple of minor comments/changes.
>
> Signed-off-by: Nayna Jain <nayna@...ux.vnet.ibm.com>
> - Defined function to convert the arch policy strings to an array of
> ima_entry_rules. The memory can then be freed after loading a custom
> policy.
> - Rename ima_get_arch_policy to arch_get_ima_policy.
> Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
> - Modified ima_init_arch_policy() and ima_init_policy() to use add_rules()
> from previous patch.
> Signed-off-by: Nayna Jain <nayna@...ux.vnet.ibm.com>
> ---
> include/linux/ima.h | 5 +++
> security/integrity/ima/ima_policy.c | 70 +++++++++++++++++++++++++++++++++++--
> 2 files changed, 73 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 4852255aa4f4..350fa957f8a6 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -39,6 +39,11 @@ static inline bool arch_ima_get_secureboot(void)
> }
> #endif
>
> +static inline const char * const *arch_get_ima_policy(void)
> +{
> + return NULL;
> +}
> +
> #else
> static inline int ima_bprm_check(struct linux_binprm *bprm)
> {
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index d5b327320d3a..5fb4b0c123a3 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -20,6 +20,7 @@
> #include <linux/rculist.h>
> #include <linux/genhd.h>
> #include <linux/seq_file.h>
> +#include <linux/ima.h>
>
> #include "ima.h"
>
> @@ -195,6 +196,9 @@ static struct ima_rule_entry secure_boot_rules[] __ro_after_init = {
> .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
> };
>
> +/* An array of architecture specific rules */
> +struct ima_rule_entry *arch_policy_entry __ro_after_init;
> +
> static LIST_HEAD(ima_default_rules);
> static LIST_HEAD(ima_policy_rules);
> static LIST_HEAD(ima_temp_rules);
> @@ -492,7 +496,6 @@ static void add_rules(struct ima_rule_entry *entries, int count,
> if (!entry)
> continue;
>
> - INIT_LIST_HEAD(&entry->list);
> list_add_tail(&entry->list, &ima_policy_rules);
Assuming that INIT_LIST_HEAD isn't needed, removing it belongs in
"[PATCH v4 3/6] ima: refactor ima_init_policy()".
> }
> if (entries[i].action == APPRAISE)
> @@ -502,6 +505,48 @@ static void add_rules(struct ima_rule_entry *entries, int count,
> }
> }
>
> +static int ima_parse_rule(char *rule, struct ima_rule_entry *entry);
> +
> +static int __init ima_init_arch_policy(void)
> +{
> + const char * const *arch_rules;
> + const char * const *rules;
> + int arch_entries = 0;
> + int i = 0;
> +
> + arch_rules = arch_get_ima_policy();
> + if (!arch_rules)
> + return arch_entries;
> +
> + /* Get number of rules */
> + for (rules = arch_rules; *rules != NULL; rules++)
> + arch_entries++;
> +
> + arch_policy_entry = kcalloc(arch_entries + 1,
> + sizeof(*arch_policy_entry), GFP_KERNEL);
> + if (!arch_policy_entry)
> + return 0;
> +
> + /* Convert each policy string rules to struct ima_rule_entry format */
> + for (rules = arch_rules, i = 0; *rules != NULL; rules++) {
> + char rule[255];
> + int result;
> +
> + result = strlcpy(rule, *rules, sizeof(rule));
> +
> + INIT_LIST_HEAD(&arch_policy_entry[i].list);
> + result = ima_parse_rule(rule, &arch_policy_entry[i]);
> + if (result) {
> + pr_warn("Skipping unknown architecture policy rule: %s\n", rule);
> + memset(&arch_policy_entry[i], 0,
> + sizeof(*arch_policy_entry));
> + continue;
> + }
> + i++;
> + }
> + return i;
> +}
> +
> /**
> * ima_init_policy - initialize the default measure rules.
> *
> @@ -510,7 +555,7 @@ static void add_rules(struct ima_rule_entry *entries, int count,
> */
> void __init ima_init_policy(void)
> {
> - int build_appraise_entries;
> + int build_appraise_entries, arch_entries;
>
> /* if !ima_policy, we load NO default rules */
> if (ima_policy)
> @@ -532,6 +577,19 @@ void __init ima_init_policy(void)
> }
>
> /*
> + * Based on runtime secure boot flags, insert arch specific measurement
> + * and appraise rules requiring file signatures for both the initial
> + * and custom policies, prior to other appraise rules.
> + * (Highest priority)
> + */
> + arch_entries = ima_init_arch_policy();
> + if (!arch_entries)
> + pr_info("No architecture policies found\n");
> + else
> + add_rules(arch_policy_entry, arch_entries,
> + IMA_DEFAULT_POLICY | IMA_CUSTOM_POLICY);
> +
> + /*
> * Insert the builtin "secure_boot" policy rules requiring file
> * signatures, prior to any other appraise rules.
> */
The architecture specific policy is higher priority, please remove
"any" in the above sentence.
> @@ -592,6 +650,14 @@ void ima_update_policy(void)
> if (ima_rules != policy) {
> ima_policy_flag = 0;
> ima_rules = policy;
> +
> + /*
> + * IMA architecture specific policy rules are specified
> + * as strings and converted to an array of ima_entry_rules
> + * on boot. After loading a custom policy, free the
> + * architecture specific rules stored as an array.
> + */
> + kfree(arch_policy_entry);
> }
> ima_update_policy_flag();
> }
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