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Message-ID: <b1b92581-56f2-b684-573f-50a66ca9fbf2@linux.vnet.ibm.com>
Date:   Mon, 31 Jul 2023 13:04:38 -0400
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Subject: Re: [PATCH v4] integrity: Always reference the blacklist keyring with
 appraisal
To:     Eric Snowberg <eric.snowberg@oracle.com>, zohar@linux.ibm.com
Cc:     dmitry.kasatkin@gmail.com, paul@paul-moore.com, jmorris@namei.org,
        serge@hallyn.com, roberto.sassu@huawei.com,
        kanth.ghatraju@oracle.com, konrad.wilk@oracle.com,
        linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org
References: <20230726211725.393056-1-eric.snowberg@oracle.com>
Content-Language: en-US
From:   Nayna <nayna@linux.vnet.ibm.com>
In-Reply-To: <20230726211725.393056-1-eric.snowberg@oracle.com>
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On 7/26/23 17:17, Eric Snowberg wrote:
> Commit 273df864cf746 ("ima: Check against blacklisted hashes for files with
> modsig") introduced an appraise_flag option for referencing the blacklist
> keyring.  Any matching binary found on this keyring fails signature
> validation. This flag only works with module appended signatures.
>
> An important part of a PKI infrastructure is to have the ability to do
> revocation at a later time should a vulnerability be found.  Expand the
> revocation flag usage to all appraisal functions. The flag is now
> enabled by default. Setting the flag with an IMA policy has been
> deprecated. Without a revocation capability like this in place, only
> authenticity can be maintained. With this change, integrity can now be
> achieved with digital signature based IMA appraisal.
>
> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
> ---
> v4 changes:
>    Fixed typo
>    Also did some performance testing with this patch. With the associative array
>    implementation used within the keyring code, there doesn't seem to be much of a
>    difference between doing  an appraisal with an empty blacklist keyring and one
>    containing 1500 entries.  At this time it is unknown how many entries a user
>    would place in this keyring, but this seemed like a bigger number than most use
>    cases.  With the 1500 entries, there were only 7 lookups to get through the
>    entire list for a file not contained within it.  For something that was
>    on the list, there was an average of 4 lookups and a single string compare.
>    Based on this testing, IMHO, there could be a lot more entries added to the
>    blacklist keyring without any real performance issues.

Nice to see the performance test results.

Reviewed-by: Nayna Jain <nayna@linux.ibm.com>

Thanks & Regards,

      - Nayna

>
> v3 changes:
>    No longer display appraise_flag=check_blacklist in the policy
>
> v2 changes:
>    Update the "case Opt_apprase_flag"
>    Removed "appraise_flag=" in the powerpc arch specific policy rules
> ---
>   Documentation/ABI/testing/ima_policy  |  6 +++---
>   arch/powerpc/kernel/ima_arch.c        |  8 ++++----
>   security/integrity/ima/ima_appraise.c | 12 +++++++-----
>   security/integrity/ima/ima_policy.c   | 17 +++++------------
>   4 files changed, 19 insertions(+), 24 deletions(-)
>
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index 49db0ff288e5..c2385183826c 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -57,9 +57,9 @@ Description:
>   				stored in security.ima xattr. Requires
>   				specifying "digest_type=verity" first.)
>
> -			appraise_flag:= [check_blacklist]
> -			Currently, blacklist check is only for files signed with appended
> -			signature.
> +			appraise_flag:= [check_blacklist] (deprecated)
> +			Setting the check_blacklist flag is no longer necessary.
> +			All appraisal functions set it by default.
>   			digest_type:= verity
>   			    Require fs-verity's file digest instead of the
>   			    regular IMA file hash.
> diff --git a/arch/powerpc/kernel/ima_arch.c b/arch/powerpc/kernel/ima_arch.c
> index 957abd592075..b7029beed847 100644
> --- a/arch/powerpc/kernel/ima_arch.c
> +++ b/arch/powerpc/kernel/ima_arch.c
> @@ -23,9 +23,9 @@ bool arch_ima_get_secureboot(void)
>    * is not enabled.
>    */
>   static const char *const secure_rules[] = {
> -	"appraise func=KEXEC_KERNEL_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
> +	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
>   #ifndef CONFIG_MODULE_SIG
> -	"appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
> +	"appraise func=MODULE_CHECK appraise_type=imasig|modsig",
>   #endif
>   	NULL
>   };
> @@ -49,9 +49,9 @@ static const char *const trusted_rules[] = {
>   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",
> +	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
>   #ifndef CONFIG_MODULE_SIG
> -	"appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
> +	"appraise func=MODULE_CHECK appraise_type=imasig|modsig",
>   #endif
>   	NULL
>   };
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 491c1aca0b1c..870dde67707b 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -458,11 +458,13 @@ int ima_check_blacklist(struct integrity_iint_cache *iint,
>   		ima_get_modsig_digest(modsig, &hash_algo, &digest, &digestsize);
>
>   		rc = is_binary_blacklisted(digest, digestsize);
> -		if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
> -			process_buffer_measurement(&nop_mnt_idmap, NULL, digest, digestsize,
> -						   "blacklisted-hash", NONE,
> -						   pcr, NULL, false, NULL, 0);
> -	}
> +	} else if (iint->flags & IMA_DIGSIG_REQUIRED && iint->ima_hash)
> +		rc = is_binary_blacklisted(iint->ima_hash->digest, iint->ima_hash->length);
> +
> +	if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
> +		process_buffer_measurement(&nop_mnt_idmap, NULL, digest, digestsize,
> +					   "blacklisted-hash", NONE,
> +					   pcr, NULL, false, NULL, 0);
>
>   	return rc;
>   }
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index c9b3bd8f1bb9..69452b79686b 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -1280,7 +1280,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
>   				     IMA_FSNAME | IMA_GID | IMA_EGID |
>   				     IMA_FGROUP | IMA_DIGSIG_REQUIRED |
>   				     IMA_PERMIT_DIRECTIO | IMA_VALIDATE_ALGOS |
> -				     IMA_VERITY_REQUIRED))
> +				     IMA_CHECK_BLACKLIST | IMA_VERITY_REQUIRED))
>   			return false;
>
>   		break;
> @@ -1355,7 +1355,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
>
>   	/* Ensure that combinations of flags are compatible with each other */
>   	if (entry->flags & IMA_CHECK_BLACKLIST &&
> -	    !(entry->flags & IMA_MODSIG_ALLOWED))
> +	    !(entry->flags & IMA_DIGSIG_REQUIRED))
>   		return false;
>
>   	/*
> @@ -1803,11 +1803,11 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>   				if (entry->flags & IMA_VERITY_REQUIRED)
>   					result = -EINVAL;
>   				else
> -					entry->flags |= IMA_DIGSIG_REQUIRED;
> +					entry->flags |= IMA_DIGSIG_REQUIRED | IMA_CHECK_BLACKLIST;
>   			} else if (strcmp(args[0].from, "sigv3") == 0) {
>   				/* Only fsverity supports sigv3 for now */
>   				if (entry->flags & IMA_VERITY_REQUIRED)
> -					entry->flags |= IMA_DIGSIG_REQUIRED;
> +					entry->flags |= IMA_DIGSIG_REQUIRED | IMA_CHECK_BLACKLIST;
>   				else
>   					result = -EINVAL;
>   			} else if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
> @@ -1816,18 +1816,13 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>   					result = -EINVAL;
>   				else
>   					entry->flags |= IMA_DIGSIG_REQUIRED |
> -						IMA_MODSIG_ALLOWED;
> +						IMA_MODSIG_ALLOWED | IMA_CHECK_BLACKLIST;
>   			} else {
>   				result = -EINVAL;
>   			}
>   			break;
>   		case Opt_appraise_flag:
>   			ima_log_string(ab, "appraise_flag", args[0].from);
> -			if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
> -			    strstr(args[0].from, "blacklist"))
> -				entry->flags |= IMA_CHECK_BLACKLIST;
> -			else
> -				result = -EINVAL;
>   			break;
>   		case Opt_appraise_algos:
>   			ima_log_string(ab, "appraise_algos", args[0].from);
> @@ -2271,8 +2266,6 @@ int ima_policy_show(struct seq_file *m, void *v)
>   	}
>   	if (entry->flags & IMA_VERITY_REQUIRED)
>   		seq_puts(m, "digest_type=verity ");
> -	if (entry->flags & IMA_CHECK_BLACKLIST)
> -		seq_puts(m, "appraise_flag=check_blacklist ");
>   	if (entry->flags & IMA_PERMIT_DIRECTIO)
>   		seq_puts(m, "permit_directio ");
>   	rcu_read_unlock();