[PATCH v10 3/8] IMA: define a hook to measure kernel integrity critical data

Tushar Sugandhi
2021-01-08T04:08:42Z

IMA provides capabilities to measure file and buffer data. However,
various data structures, policies, and states stored in kernel memory
also impact the integrity of the system. Several kernel subsystems
contain such integrity critical data. These kernel subsystems help
protect the integrity of the system. Currently, IMA does not provide a
generic function for measuring kernel integrity critical data.

Define ima_measure_critical_data, a new IMA hook, to measure kernel
integrity critical data.

Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>
---
include/linux/ima.h | 7 +++++++
security/integrity/ima/ima.h | 1 +
security/integrity/ima/ima_api.c | 2 +-
security/integrity/ima/ima_main.c | 24 ++++++++++++++++++++++++
4 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index ac3d82f962f2..37a0727c1c31 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -30,6 +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 int ima_file_hash(struct file *file, char *buf, size_t buf_size);
extern void ima_kexec_cmdline(int kernel_fd, const void *buf, int size);
+extern void ima_measure_critical_data(const char *event_name,
+ const void *buf, size_t buf_len,
+ bool hash);

#ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
extern void ima_appraise_parse_cmdline(void);
@@ -122,6 +125,10 @@ static inline int ima_file_hash(struct file *file, char *buf, size_t buf_size)
}

static inline void ima_kexec_cmdline(int kernel_fd, const void *buf, int size) {}
+
+static inline void ima_measure_critical_data(const char *event_name,
+ const void *buf, size_t buf_len,
+ bool hash) {}
#endif /* CONFIG_IMA */

#ifndef CONFIG_IMA_KEXEC
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 0b4634515839..aa312472c7c5 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -201,6 +201,7 @@ static inline unsigned int ima_hash_key(u8 *digest)
hook(POLICY_CHECK, policy) \
hook(KEXEC_CMDLINE, kexec_cmdline) \
hook(KEY_CHECK, key) \
+ hook(CRITICAL_DATA, critical_data) \
hook(MAX_CHECK, none)

#define __ima_hook_enumify(ENUM, str) ENUM,
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index e76499b1ce78..1dd70dc68ffd 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -176,7 +176,7 @@ void ima_add_violation(struct file *file, const unsigned char *filename,
* subj=, obj=, type=, func=, mask=, fsmagic=
* subj,obj, and type: are LSM specific.
* func: FILE_CHECK | BPRM_CHECK | CREDS_CHECK | MMAP_CHECK | MODULE_CHECK
- * | KEXEC_CMDLINE | KEY_CHECK
+ * | KEXEC_CMDLINE | KEY_CHECK | CRITICAL_DATA
* mask: contains the permission mask
* fsmagic: hex value
*
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 494fb964497d..ef37307e79dd 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -913,6 +913,30 @@ void ima_kexec_cmdline(int kernel_fd, const void *buf, int size)
fdput(f);
}

+/**
+ * ima_measure_critical_data - measure kernel integrity critical data
+ * @event_name: event name for the record in the IMA measurement list
+ * @buf: pointer to buffer data
+ * @buf_len: length of buffer data (in bytes)
+ * @hash: measure buffer data hash
+ *
+ * Measure data critical to the integrity of the kernel into the IMA log
+ * and extend the pcr. Examples of critical data could be various data
+ * structures, policies, and states stored in kernel memory that can
+ * impact the integrity of the system.
+ */
+void ima_measure_critical_data(const char *event_name,
+ const void *buf, size_t buf_len,
+ bool hash)
+{
+ if (!event_name || !buf || !buf_len)
+ return;
+
+ process_buffer_measurement(NULL, buf, buf_len, event_name,
+ CRITICAL_DATA, 0, NULL,
+ hash);
+}
+
static int __init init_ima(void)
{
int error;
--
2.17.1