[PATCH 3/3] ima: add pre-calculated measurements (experimental)

From: Mimi Zohar
Date: Wed Jun 22 2016 - 09:35:44 EST

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This patch defines a new IMA hook named ima_add_measurement_check()
for including pre-calculated measurements in the IMA measurement list.

Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
---
Documentation/ABI/testing/ima_policy | 2 +-
include/linux/ima.h | 12 ++++
security/integrity/ima/Kconfig | 8 +++
security/integrity/ima/ima.h | 1 +
security/integrity/ima/ima_buffer.c | 116 +++++++++++++++++++++++++++++------
security/integrity/ima/ima_policy.c | 18 +++++-
6 files changed, 136 insertions(+), 21 deletions(-)

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index 5a99c6f..e5a137e 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -28,7 +28,7 @@ Description:
base: func:= [BPRM_CHECK][MMAP_CHECK][FILE_CHECK][MODULE_CHECK]
[FIRMWARE_CHECK]
[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
- [KEXEC_CMDLINE_CHECK]
+ [KEXEC_CMDLINE_CHECK] [PRECALC_CHECK]
mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
[[^]MAY_EXEC]
fsmagic:= hex value
diff --git a/include/linux/ima.h b/include/linux/ima.h
index 88203f9..797de51 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -15,6 +15,7 @@ struct linux_binprm;

enum ima_buffer_id {
MEASURING_KEXEC_CMDLINE,
+ MEASURING_PRECALC_DATA,
MEASURING_MAX_BUFFER_ID
};

@@ -29,6 +30,9 @@ extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
extern void ima_post_path_mknod(struct dentry *dentry);
extern void ima_buffer_check(void *buf, loff_t size,
enum ima_buffer_id buffer_id);
+extern void ima_add_measurement_check(const char *hashname, u8 *digest,
+ loff_t size, enum ima_buffer_id buffer_id,
+ char *hint);

#else
static inline int ima_bprm_check(struct linux_binprm *bprm)
@@ -72,6 +76,14 @@ static inline void ima_buffer_check(void *buf, loff_t size,
{
return;
}
+
+static inline void ima_add_measurement_check(const char *hashname, u8 *digest,
+ loff_t size,
+ enum ima_buffer_id buffer_id,
+ char *hint)
+{
+ return;
+}
#endif /* CONFIG_IMA */

#ifdef CONFIG_IMA_APPRAISE
diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 5487827..0fb54d3 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -44,6 +44,14 @@ config IMA_LSM_RULES
help
Disabling this option will disregard LSM based policy rules.

+config IMA_PRECALC_RULES
+ bool "Permit pre-calculated measurements (EXPERIMENTAL)"
+ depends on IMA
+ default n
+ help
+ Enabling this option will permit pre-calculated measurements
+ to be added to the IMA measurement list.
+
choice
prompt "Default template"
default IMA_NG_TEMPLATE
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 5f21a9a..ccad21d 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -152,6 +152,7 @@ enum ima_hooks {
KEXEC_INITRAMFS_CHECK,
KEXEC_CMDLINE_CHECK,
POLICY_CHECK,
+ PRECALC_CHECK,
MAX_CHECK
};

diff --git a/security/integrity/ima/ima_buffer.c b/security/integrity/ima/ima_buffer.c
index e74131b..ad49f6c 100644
--- a/security/integrity/ima/ima_buffer.c
+++ b/security/integrity/ima/ima_buffer.c
@@ -11,6 +11,8 @@
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/ima.h>
+#include <crypto/hash_info.h>
+#include <linux/string_helpers.h>

#include "ima.h"

@@ -21,9 +23,37 @@ struct buffer_idmap {

static struct buffer_idmap _idmap[MEASURING_MAX_BUFFER_ID] = {
[MEASURING_KEXEC_CMDLINE].func = KEXEC_CMDLINE_CHECK,
- [MEASURING_KEXEC_CMDLINE].buf = "boot-cmdline",
+ [MEASURING_KEXEC_CMDLINE].buf = "kexec-boot-cmdline",
+ [MEASURING_PRECALC_DATA].func = PRECALC_CHECK,
+ [MEASURING_PRECALC_DATA].buf = "precalc",
};

+#define IMA_MAX_BUFFER_HINT_SIZE 255
+
+static int store_buffer_measurement(struct ima_digest_data *hash, int pcr,
+ char *buffer_hint)
+{
+ struct ima_template_entry *entry;
+ struct integrity_iint_cache tmp_iint, *iint = &tmp_iint;
+ struct ima_event_data event_data = {iint, NULL, NULL, NULL, 0, NULL};
+ int violation = 0;
+ int result;
+
+ iint->ima_hash = hash;
+ event_data.filename = buffer_hint;
+
+ result = ima_alloc_init_template(&event_data, &entry);
+ if (result < 0)
+ return result;
+
+ result = ima_store_template(entry, violation, NULL,
+ event_data.filename, pcr);
+ if (result < 0)
+ ima_free_template_entry(entry);
+
+ return result;
+}
+
static void process_buffer_measurement(void *buf, loff_t size,
enum ima_buffer_id buffer_id, int pcr)
{
@@ -31,10 +61,6 @@ static void process_buffer_measurement(void *buf, loff_t size,
struct ima_digest_data hdr;
char digest[IMA_MAX_DIGEST_SIZE];
} hash;
- struct ima_template_entry *entry;
- struct integrity_iint_cache tmp_iint, *iint = &tmp_iint;
- struct ima_event_data event_data = {iint, NULL, NULL, NULL, 0, NULL};
- int violation = 0;
int result;

memset(&hash, 0, sizeof(hash));
@@ -45,20 +71,10 @@ static void process_buffer_measurement(void *buf, loff_t size,
return;
}

- iint->ima_hash = &hash.hdr;
- event_data.filename = _idmap[buffer_id].buf;
- result = ima_alloc_init_template(&event_data, &entry);
- if (result < 0) {
- pr_debug("failed allocating template\n");
- return;
- }
-
- result = ima_store_template(entry, violation, NULL,
- event_data.filename, pcr);
- if (result < 0) {
+ result = store_buffer_measurement(&hash.hdr, pcr,
+ _idmap[buffer_id].buf);
+ if (result < 0)
pr_debug("failed storing buffer measurement\n");
- ima_free_template_entry(entry);
- }
}

/**
@@ -82,3 +98,67 @@ void ima_buffer_check(void *buf, loff_t size, enum ima_buffer_id buffer_id)
process_buffer_measurement(buf, size, buffer_id, pcr);
}
EXPORT_SYMBOL_GPL(ima_buffer_check);
+
+/**
+ * ima_add_measurement_check - add pre-calculated hash measurement
+ * @hashname: pointer to hash algorithm name
+ * @digest: pointer to hash digest
+ * @size: hash digest size
+ * @buffer_id: caller identifier
+ * @hint: measurement identifier
+ *
+ * Include pre-calculated hash measurements in the IMA measurement list.
+ */
+void ima_add_measurement_check(const char *hashname, u8 *digest, loff_t size,
+ enum ima_buffer_id buffer_id, char *hint)
+{
+ struct {
+ struct ima_digest_data hdr;
+ char digest[IMA_MAX_DIGEST_SIZE];
+ } hash;
+ int pcr = CONFIG_IMA_MEASURE_PCR_IDX;
+ char buffer_hint[IMA_MAX_BUFFER_HINT_SIZE];
+ char *buf;
+ int result, i;
+
+ if (buffer_id > MEASURING_MAX_BUFFER_ID)
+ return;
+
+ if (!ima_match_buffer_id(_idmap[buffer_id].func, &pcr))
+ return;
+
+ if (!hint) {
+ pr_debug("missing buffer hint\n");
+ return;
+ }
+
+ buf = kstrdup_quotable(hint, GFP_KERNEL);
+ if (!buf) {
+ pr_debug("failed quoting buffer hint\n");
+ return;
+ }
+
+ /* Limit the total measurement hint to IMA_MAX_BUFFER_HINT_SIZE. */
+ snprintf(buffer_hint, sizeof(buffer_hint), "(%s) %s",
+ _idmap[buffer_id].buf, buf);
+ kfree(buf);
+
+ memset(&hash, 0, sizeof(hash));
+ for (i = 1; i < HASH_ALGO__LAST; i++) {
+ if (strcmp(hashname, hash_algo_name[i]) != 0)
+ continue;
+ hash.hdr.algo = i;
+ break;
+ }
+ if (hash.hdr.algo == 0) {
+ pr_debug("invalid hash algorithm (%d)\n", hash.hdr.algo);
+ return;
+ }
+
+ hash.hdr.length = size;
+ memcpy(&hash.hdr.digest, digest, size);
+ result = store_buffer_measurement(&hash.hdr, pcr, buffer_hint);
+ if (result < 0)
+ pr_debug("failed to store buffer measurement\n");
+}
+EXPORT_SYMBOL_GPL(ima_add_measurement_check);
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 8e53f84..4094dd7 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"

@@ -54,6 +55,12 @@ enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,

enum policy_types { ORIGINAL_TCB = 1, DEFAULT_TCB };

+#ifdef CONFIG_MEASURING_PRECALC_RULES
+static int permit_measuring_precalc_rules = 1;
+#else
+static int permit_measuring_precalc_rules;
+#endif
+
struct ima_rule_entry {
struct list_head list;
int action;
@@ -668,6 +675,9 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
entry->func = KEXEC_CMDLINE_CHECK;
else if (strcmp(args[0].from, "POLICY_CHECK") == 0)
entry->func = POLICY_CHECK;
+ else if ((strcmp(args[0].from, "PRECALC_CHECK") == 0)
+ && permit_measuring_precalc_rules)
+ entry->func = PRECALC_CHECK;
else
result = -EINVAL;
if (!result)
@@ -929,7 +939,7 @@ enum {
func_file = 0, func_mmap, func_bprm,
func_module, func_firmware, func_post,
func_kexec_kernel, func_kexec_initramfs,
- func_kexec_cmdline, func_policy
+ func_kexec_cmdline, func_policy, func_precalc
};

static char *func_tokens[] = {
@@ -942,7 +952,8 @@ static char *func_tokens[] = {
"KEXEC_KERNEL_CHECK",
"KEXEC_INITRAMFS_CHECK",
"KEXEC_CMDLINE_CHECK",
- "POLICY_CHECK"
+ "POLICY_CHECK",
+ "PRECALC_CHECK"
};

void *ima_policy_start(struct seq_file *m, loff_t *pos)
@@ -1019,6 +1030,9 @@ static void policy_func_show(struct seq_file *m, enum ima_hooks func)
case POLICY_CHECK:
seq_printf(m, pt(Opt_func), ft(func_policy));
break;
+ case PRECALC_CHECK:
+ seq_printf(m, pt(Opt_func), ft(func_precalc));
+ break;
default:
snprintf(tbuf, sizeof(tbuf), "%d", func);
seq_printf(m, pt(Opt_func), tbuf);
--
2.1.0

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