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Date: Thu, 10 Dec 2020 17:02:18 -0600
From: Tyler Hicks <tyhicks@...ux.microsoft.com>
To: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
Cc: zohar@...ux.ibm.com, stephen.smalley.work@...il.com,
casey@...aufler-ca.com, agk@...hat.com, snitzer@...hat.com,
gmazyland@...il.com, paul@...l-moore.com, sashal@...nel.org,
jmorris@...ei.org, nramas@...ux.microsoft.com,
linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: Re: [PATCH v7 3/8] IMA: define a hook to measure kernel integrity
critical data
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@...ux.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
>
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