From: Thiago Jung Bauermann Subject: [PATCH v6 09/12] ima: Add modsig appraise_type option for module-style appended signatures Date: Fri, 16 Mar 2018 17:38:34 -0300 Message-ID: <20180316203837.10174-10-bauerman@linux.vnet.ibm.com> References: <20180316203837.10174-1-bauerman@linux.vnet.ibm.com> Cc: linux-security-module@vger.kernel.org, keyrings@vger.kernel.org, linux-crypto@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Mimi Zohar , Dmitry Kasatkin , James Morris , "Serge E. Hallyn" , David Howells , David Woodhouse , Jessica Yu , Herbert Xu , "David S. Miller" , "AKASHI, Takahiro" , Thiago Jung Bauermann To: linux-integrity@vger.kernel.org Return-path: In-Reply-To: <20180316203837.10174-1-bauerman@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org This patch introduces the modsig keyword to the IMA policy syntax to specify that a given hook should expect the file to have the IMA signature appended to it. Here is how it can be used in a rule: appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig With this rule, IMA will accept either a signature stored in the extended attribute or an appended signature. For now, the rule above will behave exactly the same as if appraise_type=imasig was specified because the actual modsig implementation will be introduced in a separate patch. Suggested-by: Mimi Zohar Signed-off-by: Thiago Jung Bauermann --- Documentation/ABI/testing/ima_policy | 6 +++++- security/integrity/ima/Kconfig | 10 ++++++++++ security/integrity/ima/Makefile | 1 + security/integrity/ima/ima.h | 9 +++++++++ security/integrity/ima/ima_modsig.c | 31 +++++++++++++++++++++++++++++++ security/integrity/ima/ima_policy.c | 12 ++++++++++-- security/integrity/integrity.h | 1 + 7 files changed, 67 insertions(+), 3 deletions(-) diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy index b8465e00ba5f..835d9da9b26e 100644 --- a/Documentation/ABI/testing/ima_policy +++ b/Documentation/ABI/testing/ima_policy @@ -37,7 +37,7 @@ Description: euid:= decimal value fowner:= decimal value lsm: are LSM specific - option: appraise_type:= [imasig] + option: appraise_type:= [imasig] [imasig|modsig] pcr:= decimal value default policy: @@ -103,3 +103,7 @@ Description: measure func=KEXEC_KERNEL_CHECK pcr=4 measure func=KEXEC_INITRAMFS_CHECK pcr=5 + + Example of appraise rule allowing modsig appended signatures: + + appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig index 6a8f67714c83..ee278189e0bb 100644 --- a/security/integrity/ima/Kconfig +++ b/security/integrity/ima/Kconfig @@ -164,6 +164,16 @@ config IMA_APPRAISE_BOOTPARAM This option enables the different "ima_appraise=" modes (eg. fix, log) from the boot command line. +config IMA_APPRAISE_MODSIG + bool "Support module-style signatures for appraisal" + depends on IMA_APPRAISE + default n + help + Adds support for signatures appended to files. The format of the + appended signature is the same used for signed kernel modules. + The modsig keyword can be used in the IMA policy to allow a hook + to accept such signatures. + config IMA_TRUSTED_KEYRING bool "Require all keys on the .ima keyring be signed (deprecated)" depends on IMA_APPRAISE && SYSTEM_TRUSTED_KEYRING diff --git a/security/integrity/ima/Makefile b/security/integrity/ima/Makefile index d921dc4f9eb0..31d57cdf2421 100644 --- a/security/integrity/ima/Makefile +++ b/security/integrity/ima/Makefile @@ -9,5 +9,6 @@ obj-$(CONFIG_IMA) += ima.o ima-y := ima_fs.o ima_queue.o ima_init.o ima_main.o ima_crypto.o ima_api.o \ ima_policy.o ima_template.o ima_template_lib.o ima-$(CONFIG_IMA_APPRAISE) += ima_appraise.o +ima-$(CONFIG_IMA_APPRAISE_MODSIG) += ima_modsig.o ima-$(CONFIG_HAVE_IMA_KEXEC) += ima_kexec.o obj-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index 99f2bab15009..c61d8fc5190d 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -299,6 +299,15 @@ static inline int ima_read_xattr(struct dentry *dentry, #endif /* CONFIG_IMA_APPRAISE */ +#ifdef CONFIG_IMA_APPRAISE_MODSIG +bool ima_hook_supports_modsig(enum ima_hooks func); +#else +static inline bool ima_hook_supports_modsig(enum ima_hooks func) +{ + return false; +} +#endif /* CONFIG_IMA_APPRAISE_MODSIG */ + /* LSM based policy rules require audit */ #ifdef CONFIG_IMA_LSM_RULES diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c new file mode 100644 index 000000000000..d8ea811b6f74 --- /dev/null +++ b/security/integrity/ima/ima_modsig.c @@ -0,0 +1,31 @@ +// SPDX-License-Identifier: GPL-2.0+ +/* + * IMA support for appraising module-style appended signatures. + * + * Copyright (C) 2018 IBM Corporation + * + * Author: + * Thiago Jung Bauermann + */ + +#include "ima.h" + +/** + * ima_hook_supports_modsig - can the policy allow modsig for this hook? + * + * modsig is only supported by hooks using ima_post_read_file, because only they + * preload the contents of the file in a buffer. FILE_CHECK does that in some + * cases, but not when reached from vfs_open. POLICY_CHECK can support it, but + * it's not useful in practice because it's a text file so deny. + */ +bool ima_hook_supports_modsig(enum ima_hooks func) +{ + switch (func) { + case FIRMWARE_CHECK: + case KEXEC_KERNEL_CHECK: + case KEXEC_INITRAMFS_CHECK: + return true; + default: + return false; + } +} diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index 833da24c7009..e7421fd94277 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -887,6 +887,10 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) ima_log_string(ab, "appraise_type", args[0].from); if ((strcmp(args[0].from, "imasig")) == 0) entry->flags |= IMA_DIGSIG_REQUIRED; + else if (ima_hook_supports_modsig(entry->func) && + strcmp(args[0].from, "imasig|modsig") == 0) + entry->flags |= IMA_DIGSIG_REQUIRED + | IMA_MODSIG_ALLOWED; else result = -EINVAL; break; @@ -1176,8 +1180,12 @@ int ima_policy_show(struct seq_file *m, void *v) } } } - if (entry->flags & IMA_DIGSIG_REQUIRED) - seq_puts(m, "appraise_type=imasig "); + if (entry->flags & IMA_DIGSIG_REQUIRED) { + if (entry->flags & IMA_MODSIG_ALLOWED) + seq_puts(m, "appraise_type=imasig|modsig "); + else + seq_puts(m, "appraise_type=imasig "); + } if (entry->flags & IMA_PERMIT_DIRECTIO) seq_puts(m, "permit_directio "); rcu_read_unlock(); diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h index 4c381b992e11..6643c6550787 100644 --- a/security/integrity/integrity.h +++ b/security/integrity/integrity.h @@ -35,6 +35,7 @@ #define IMA_NEW_FILE 0x04000000 #define EVM_IMMUTABLE_DIGSIG 0x08000000 #define IMA_FAIL_UNVERIFIABLE_SIGS 0x10000000 +#define IMA_MODSIG_ALLOWED 0x20000000 #define IMA_DO_MASK (IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \ IMA_HASH | IMA_APPRAISE_SUBMASK)