[PATCH v7 3/8] IMA: define a hook to measure kernel integrity critical data

[Tyler Hicks]

On 2020-12-09 11:42:07, Tushar Sugandhi wrote:
> IMA provides capabilities to measure file data, and in-memory 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 a device. Currently,
> IMA does not provide a generic function for kernel subsystems to measure
> their integrity critical data.
>  
> Define a new IMA hook - ima_measure_critical_data to measure kernel
> integrity critical data.
> 
> Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>
> ---
>  Documentation/ABI/testing/ima_policy |  2 +-
>  include/linux/ima.h                  |  6 +++++
>  security/integrity/ima/ima.h         |  1 +
>  security/integrity/ima/ima_api.c     |  2 +-
>  security/integrity/ima/ima_main.c    | 36 ++++++++++++++++++++++++++++
>  security/integrity/ima/ima_policy.c  |  2 ++
>  6 files changed, 47 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index e35263f97fc1..6ec7daa87cba 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -32,7 +32,7 @@ Description:
>  			func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK]MODULE_CHECK]
>  			        [FIRMWARE_CHECK]
>  				[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
> -				[KEXEC_CMDLINE] [KEY_CHECK]
> +				[KEXEC_CMDLINE] [KEY_CHECK] [CRITICAL_DATA]
>  			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 ac3d82f962f2..675f54db6264 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, int buf_len,
> +				      bool measure_buf_hash);
>  
>  #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
>  extern void ima_appraise_parse_cmdline(void);
> @@ -122,6 +125,9 @@ 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, int buf_len,
> +					     bool measure_buf_hash) {}
>  #endif /* CONFIG_IMA */
>  
>  #ifndef CONFIG_IMA_KEXEC
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index fa3044a7539f..7d9deda6a8b3 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 af218babd198..9917e1730cb6 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 03aad13e9e70..ae59f4a4dd70 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -922,6 +922,42 @@ 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 to be used for the buffer entry
> + * @buf: pointer to buffer containing data to measure
> + * @buf_len: length of buffer(in bytes)
> + * @measure_buf_hash: measure buffer hash
> + *
> + * Measure the kernel subsystem data, critical to the integrity of the kernel,
> + * into the IMA log and extend the @pcr.
> + *
> + * Use @event_name to describe the state/buffer data change.
> + * Examples of critical data (buf) could be kernel in-memory r/o structures,
                                 ^
				 @buf

> + * hash of the memory structures, or data that represents subsystem state
> + * change.
> + *
> + * If @measure_buf_hash is set to true - measure hash of the buffer data,
> + * else measure the buffer data itself.
> + * measure_buf_hash can be used to save space, if the data being measured
      ^
      @measure_buf_hash

> + * is too large.
> + *
> + * The data (buf) can only be measured, not appraised.
                ^
		@buf

> + */
> +void ima_measure_critical_data(const char *event_name,
> +			       const void *buf, int buf_len,
> +			       bool measure_buf_hash)
> +{
> +	if (!event_name || !buf || !buf_len) {
> +		pr_err("Invalid arguments passed to %s().\n", __func__);

This is a problem for the developer making use of the
ima_measure_critical_data() API and shouldn't be logged, IMO, because a
user/admin can do nothing about it. I think the error message should be
dropped.

> +		return;
> +	}
> +
> +	process_buffer_measurement(NULL, buf, buf_len, event_name,
> +				   CRITICAL_DATA, 0, NULL,
> +				   measure_buf_hash);
> +}
> +
>  static int __init init_ima(void)
>  {
>  	int error;
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 25419c7ff50b..2a0c0603626e 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -1251,6 +1251,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>  			else if (IS_ENABLED(CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS) &&
>  				 strcmp(args[0].from, "KEY_CHECK") == 0)
>  				entry->func = KEY_CHECK;
> +			else if (strcmp(args[0].from, "CRITICAL_DATA") == 0)
> +				entry->func = CRITICAL_DATA;
>  			else
>  				result = -EINVAL;
>  			if (!result)

This hunk and the above change to Documentation/ABI/testing/ima_policy
need to be moved to the next patch when you introduce the policy
changes.

Tyler

> -- 
> 2.17.1
>