[PATCH v7 10/14] ima: Add modsig appraise_type option for module-style appended signatures
From: Thiago Jung Bauermann
Date: Tue May 22 2018 - 19:34:00 EST
Introduce 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. The actual modsig implementation
will be introduced separately.
Suggested-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
---
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 74c6702de74e..9d1dfd0a8891 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 567be3c6568c..01f379916583 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -298,6 +298,15 @@ 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 <bauerman@xxxxxxxxxxxxxxxxxx>
+ */
+
+#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 d454949493c6..66d0d3bcf1b2 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -919,6 +919,10 @@ 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;
@@ -1211,8 +1215,12 @@ 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 7f80c3e44d51..05fdbf953f90 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)