[PATCH v5 0/2] IMA: Deferred measurement of keys

[PATCH v5 0/2] IMA: Deferred measurement of keys

[Lakshmi Ramasubramanian]

This patchset extends the previous version[1] by adding support for
deferred processing of keys.

With the patchset referenced above, the IMA subsystem supports
measuring asymmetric keys when the key is created or updated.
But keys created or updated before a custom IMA policy is loaded
are currently not measured. This includes keys added to, for instance,
.builtin_trusted_keys which happens early in the boot process.

This change adds support for queuing keys created or updated before
a custom IMA policy is loaded. The queued keys are processed when
a custom policy is loaded. Keys created or updated after a custom policy
is loaded are measured immediately (not queued).

If the kernel is built with both CONFIG_IMA and
CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE enabled then the IMA policy
must be applied as a custom policy. Not providing a custom policy
in the above configuration would result in asymmeteric keys being queued
until a custom policy is loaded. This is by design.

[1] https://lore.kernel.org/linux-integrity/20191211164707.4698-1-nramas@linux.microsoft.com/

Testing performed:

  * Booted the kernel with this change.
  * Added .builtin_trusted_keys in "keyrings=" option in
    the IMA policy and verified the keys added to this
    keyring are measured.
  * Specified only func=KEY_CHECK and not "keyrings=" option,
    and verified the keys added to builtin_trusted_keys keyring
    are processed.
  * Added keys at runtime and verified they are measured
    if the IMA policy permitted.
      => For example, added keys to .ima keyring and verified.

Changelog:

  v5

  => Removed temp keys list in ima_process_queued_keys()

  v4

  => Check and set ima_process_keys flag with mutex held.

  v3

  => Defined ima_process_keys flag to be static.
  => Set ima_process_keys with ima_keys_mutex held.
  => Added a comment in ima_process_queued_keys() function
     to state the use of temporary list for keys.

  v2

  => Rebased the changes to v5.5-rc1
  => Updated function names, variable names, and code comments
     to be less verbose.

  v1

  => Code cleanup

  v0

  => Based changes on v5.4-rc8
  => The following patchsets should be applied in that order
     https://lore.kernel.org/linux-integrity/1572492694-6520-1-git-send-email-zohar@linux.ibm.com
     https://lore.kernel.org/linux-integrity/20191204224131.3384-1-nramas@linux.microsoft.com/
  => Added functions to queue and dequeue keys, and process
     the queued keys when custom IMA policies are applied.

Lakshmi Ramasubramanian (2):
  IMA: Define workqueue for early boot key measurements
  IMA: Call workqueue functions to measure queued keys

 security/integrity/ima/ima.h                 |  15 +++
 security/integrity/ima/ima_asymmetric_keys.c | 123 +++++++++++++++++++
 security/integrity/ima/ima_policy.c          |   3 +
 3 files changed, 141 insertions(+)

-- 
2.17.1

[PATCH v5 1/2] IMA: Define workqueue for early boot "key" measurements

[Lakshmi Ramasubramanian]

Measuring keys requires a custom IMA policy to be loaded.
Keys created or updated before a custom IMA policy is loaded should
be queued and the keys should be processed after a custom policy
is loaded.

This patch defines workqueue for queuing keys when a custom IMA policy
has not yet been loaded.

A flag namely ima_process_keys is used to check if the key should be
queued or should be processed immediately.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
---
 security/integrity/ima/ima.h                 |  15 +++
 security/integrity/ima/ima_asymmetric_keys.c | 115 +++++++++++++++++++
 2 files changed, 130 insertions(+)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index f06238e41a7c..97f8a4078483 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -205,6 +205,21 @@ extern const char *const func_tokens[];
 
 struct modsig;
 
+#ifdef CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+/*
+ * To track keys that need to be measured.
+ */
+struct ima_key_entry {
+	struct list_head list;
+	void *payload;
+	size_t payload_len;
+	char *keyring_name;
+};
+void ima_process_queued_keys(void);
+#else
+static inline void ima_process_queued_keys(void) {}
+#endif /* CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE */
+
 /* LIM API function definitions */
 int ima_get_action(struct inode *inode, const struct cred *cred, u32 secid,
 		   int mask, enum ima_hooks func, int *pcr,
diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
index fea2e7dd3b09..d520a67180d8 100644
--- a/security/integrity/ima/ima_asymmetric_keys.c
+++ b/security/integrity/ima/ima_asymmetric_keys.c
@@ -14,6 +14,121 @@
 #include <keys/asymmetric-type.h>
 #include "ima.h"
 
+/*
+ * Flag to indicate whether a key can be processed
+ * right away or should be queued for processing later.
+ */
+static bool ima_process_keys;
+
+/*
+ * To synchronize access to the list of keys that need to be measured
+ */
+static DEFINE_MUTEX(ima_keys_mutex);
+static LIST_HEAD(ima_keys);
+
+static void ima_free_key_entry(struct ima_key_entry *entry)
+{
+	if (entry) {
+		kfree(entry->payload);
+		kfree(entry->keyring_name);
+		kfree(entry);
+	}
+}
+
+static struct ima_key_entry *ima_alloc_key_entry(
+	struct key *keyring,
+	const void *payload, size_t payload_len)
+{
+	int rc = 0;
+	struct ima_key_entry *entry;
+
+	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+	if (entry) {
+		entry->payload = kmemdup(payload, payload_len, GFP_KERNEL);
+		entry->keyring_name = kstrdup(keyring->description,
+					      GFP_KERNEL);
+		entry->payload_len = payload_len;
+	}
+
+	if ((entry == NULL) || (entry->payload == NULL) ||
+	    (entry->keyring_name == NULL)) {
+		rc = -ENOMEM;
+		goto out;
+	}
+
+	INIT_LIST_HEAD(&entry->list);
+
+out:
+	if (rc) {
+		ima_free_key_entry(entry);
+		entry = NULL;
+	}
+
+	return entry;
+}
+
+bool ima_queue_key(struct key *keyring, const void *payload,
+		   size_t payload_len)
+{
+	bool queued = false;
+	struct ima_key_entry *entry;
+
+	entry = ima_alloc_key_entry(keyring, payload, payload_len);
+	if (!entry)
+		return false;
+
+	mutex_lock(&ima_keys_mutex);
+	if (!ima_process_keys) {
+		list_add_tail(&entry->list, &ima_keys);
+		queued = true;
+	}
+	mutex_unlock(&ima_keys_mutex);
+
+	if (!queued)
+		ima_free_key_entry(entry);
+
+	return queued;
+}
+
+/*
+ * ima_process_queued_keys() - process keys queued for measurement
+ *
+ * This function sets ima_process_keys to true and processes queued keys.
+ * From here on keys will be processed right away (not queued).
+ */
+void ima_process_queued_keys(void)
+{
+	struct ima_key_entry *entry, *tmp;
+	bool process = false;
+
+	if (ima_process_keys)
+		return;
+
+	/*
+	 * Since ima_process_keys is set to true, any new key will be
+	 * processed immediately and not be queued to ima_keys list.
+	 * First one setting the ima_process_keys flag to true will
+	 * process the queued keys.
+	 */
+	mutex_lock(&ima_keys_mutex);
+	if (!ima_process_keys) {
+		ima_process_keys = true;
+		process = true;
+	}
+	mutex_unlock(&ima_keys_mutex);
+
+	if (!process)
+		return;
+
+	list_for_each_entry_safe(entry, tmp, &ima_keys, list) {
+		process_buffer_measurement(entry->payload, entry->payload_len,
+					   entry->keyring_name, KEY_CHECK, 0,
+					   entry->keyring_name);
+		list_del(&entry->list);
+		ima_free_key_entry(entry);
+	}
+}
+
 /**
  * ima_post_key_create_or_update - measure asymmetric keys
  * @keyring: keyring to which the key is linked to
-- 
2.17.1

[PATCH v5 2/2] IMA: Call workqueue functions to measure queued keys

[Lakshmi Ramasubramanian]

Measuring keys requires a custom IMA policy to be loaded.
Keys should be queued for measurement if a custom IMA policy
is not yet loaded. Keys queued for measurement, if any, should be
processed when a custom IMA policy is loaded.

This patch updates the IMA hook function ima_post_key_create_or_update()
to queue the key if a custom IMA policy has not yet been loaded.
And, ima_update_policy() function, which is called when
a custom IMA policy is loaded, is updated to process queued keys.

Sample "key" measurement rule in the IMA policy:

measure func=KEY_CHECK uid=0 keyrings=.ima|.builtin_trusted_keys template=ima-buf

If the kernel is built with one or more built-in trusted certificates,
IMA measurement should list all the keys imported from those certificates.

Display "key" measurement in the IMA measurement list:

cat /sys/kernel/security/ima/ascii_runtime_measurements

10 faf3...e702 ima-buf sha256:27c915b8ddb9fae7214cf0a8a7043cc3eeeaa7539bcb136f8427067b5f6c3b7b .builtin_trusted_keys 308202863082...4aee

Verify "key" measurement data for a key added to ".builtin_trusted_keys" keyring:

cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements | grep -m 1 "\.builtin_trusted_keys" | cut -d' ' -f 6 | xxd -r -p |tee btk-cert.der | sha256sum | cut -d' ' -f 1

The output of the above command should match the template hash
of the first "key" measurement entry in the IMA measurement list for
the key added to ".builtin_trusted_keys" keyring.

The file namely "btk-cert.der" generated by the above command
should be a valid x509 certificate (in DER format) and should match
the one that was used to import the key to the ".builtin_trusted_keys" keyring.
The certificate file can be verified using openssl tool.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
---
 security/integrity/ima/ima_asymmetric_keys.c | 8 ++++++++
 security/integrity/ima/ima_policy.c          | 3 +++
 2 files changed, 11 insertions(+)

diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
index d520a67180d8..4124f10ff0c2 100644
--- a/security/integrity/ima/ima_asymmetric_keys.c
+++ b/security/integrity/ima/ima_asymmetric_keys.c
@@ -145,6 +145,8 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
 				   const void *payload, size_t payload_len,
 				   unsigned long flags, bool create)
 {
+	bool queued = false;
+
 	/* Only asymmetric keys are handled by this hook. */
 	if (key->type != &key_type_asymmetric)
 		return;
@@ -152,6 +154,12 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
 	if (!payload || (payload_len == 0))
 		return;
 
+	if (!ima_process_keys)
+		queued = ima_queue_key(keyring, payload, payload_len);
+
+	if (queued)
+		return;
+
 	/*
 	 * keyring->description points to the name of the keyring
 	 * (such as ".builtin_trusted_keys", ".ima", etc.) to
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index a4dde9d575b2..04b9c6c555de 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -807,6 +807,9 @@ void ima_update_policy(void)
 		kfree(arch_policy_entry);
 	}
 	ima_update_policy_flag();
+
+	/* Custom IMA policy has been loaded */
+	ima_process_queued_keys();
 }
 
 /* Keep the enumeration in sync with the policy_tokens! */
-- 
2.17.1

Re: [PATCH v5 1/2] IMA: Define workqueue for early boot "key" measurements

[Mimi Zohar]

On Wed, 2019-12-18 at 08:44 -0800, Lakshmi Ramasubramanian wrote:
> +/*
> + * ima_process_queued_keys() - process keys queued for measurement
> + *
> + * This function sets ima_process_keys to true and processes queued keys.
> + * From here on keys will be processed right away (not queued).
> + */
> +void ima_process_queued_keys(void)
> +{
> +	struct ima_key_entry *entry, *tmp;
> +	bool process = false;
> +
> +	if (ima_process_keys)
> +		return;
> +
> +	/*
> +	 * Since ima_process_keys is set to true, any new key will be
> +	 * processed immediately and not be queued to ima_keys list.
> +	 * First one setting the ima_process_keys flag to true will
> +	 * process the queued keys.
> +	 */
> +	mutex_lock(&ima_keys_mutex);
> +	if (!ima_process_keys) {
> +		ima_process_keys = true;
> +		process = true;
> +	}
> +	mutex_unlock(&ima_keys_mutex);
> +
> +	if (!process)
> +		return;
> +
> +	list_for_each_entry_safe(entry, tmp, &ima_keys, list) {
> +		process_buffer_measurement(entry->payload, entry->payload_len,
> +					   entry->keyring_name, KEY_CHECK, 0,
> +					   entry->keyring_name);
> +		list_del(&entry->list);
> +		ima_free_key_entry(entry);
> +	}
> +}
> +

Getting rid of the temporary list is definitely a big improvement.  As
James suggested, using test_and_set_bit() and test_bit() would improve
this code even more.  I think, James correct me if I'm wrong, you
would be able to get rid of both the mutex and "process".

Mimi


>  /**
>   * ima_post_key_create_or_update - measure asymmetric keys
>   * @keyring: keyring to which the key is linked to

Re: [PATCH v5 1/2] IMA: Define workqueue for early boot "key" measurements

[Lakshmi Ramasubramanian]

On 12/19/19 5:11 AM, Mimi Zohar wrote:

> 
> Getting rid of the temporary list is definitely a big improvement.  As
> James suggested, using test_and_set_bit() and test_bit() would improve
> this code even more.  I think, James correct me if I'm wrong, you
> would be able to get rid of both the mutex and "process".
> 
> Mimi

I am not sure if the mutex can be removed.

In ima_queue_key() we need to test the flag and add the key to the list 
as an atomic operation:

  if (!test_bit())
     insert_key_to_list

Suppose the if condition is true, but before we could insert the key to 
the list, ima_process_queued_keys() runs and processes queued keys we'll 
add the key to the list and never process it.

Is there an API in the kernel to test and add an entry to a list 
atomically?

thanks,
  -lakshmi

Re: [PATCH v5 1/2] IMA: Define workqueue for early boot "key" measurements

[Mimi Zohar]

On Thu, 2019-12-19 at 08:55 -0800, Lakshmi Ramasubramanian wrote:
> I am not sure if the mutex can be removed.
> 
> In ima_queue_key() we need to test the flag and add the key to the list 
> as an atomic operation:
> 
>   if (!test_bit())
>      insert_key_to_list
> 
> Suppose the if condition is true, but before we could insert the key to 
> the list, ima_process_queued_keys() runs and processes queued keys we'll 
> add the key to the list and never process it.
> 
> Is there an API in the kernel to test and add an entry to a list 
> atomically?

Ok, using test_and_set_bit() and test_bit() only helps, if we can get
rid of the mutex.  I'll queue these patches.

thanks,

Mimi

Re: [PATCH v5 0/2] IMA: Deferred measurement of keys

[Mimi Zohar]

On Wed, 2019-12-18 at 08:44 -0800, Lakshmi Ramasubramanian wrote:
> This patchset extends the previous version[1] by adding support for
> deferred processing of keys.
> 
> With the patchset referenced above, the IMA subsystem supports
> measuring asymmetric keys when the key is created or updated.
> But keys created or updated before a custom IMA policy is loaded
> are currently not measured. This includes keys added to, for instance,
> .builtin_trusted_keys which happens early in the boot process.
> 
> This change adds support for queuing keys created or updated before
> a custom IMA policy is loaded. The queued keys are processed when
> a custom policy is loaded. Keys created or updated after a custom policy
> is loaded are measured immediately (not queued).
> 
> If the kernel is built with both CONFIG_IMA and
> CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE enabled then the IMA policy
> must be applied as a custom policy. Not providing a custom policy
> in the above configuration would result in asymmeteric keys being queued
> until a custom policy is loaded. This is by design.

I didn't notice the "This is by design" here, referring to the memory
never being freed.  "This is by design" was suppose to refer to
requiring a custom policy for measuring keys.

For now, these two patches are queued in the next-integrity-testing
branch, but I would appreciate your addressing not freeing the memory
associated with the keys, if a custom policy is not loaded.

Please note that I truncated the 2/2 patch description, as it repeats
the existing verification example in commit ("2b60c0ecedf8 IMA: Read
keyrings= option from the IMA policy").

thanks,

Mimi

Re: [PATCH v5 0/2] IMA: Deferred measurement of keys

[Lakshmi Ramasubramanian]

On 12/20/2019 11:01 AM, Mimi Zohar wrote:

Hi Mimi,

>> If the kernel is built with both CONFIG_IMA and
>> CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE enabled then the IMA policy
>> must be applied as a custom policy. Not providing a custom policy
>> in the above configuration would result in asymmeteric keys being queued
>> until a custom policy is loaded. This is by design.
> 
> I didn't notice the "This is by design" here, referring to the memory
> never being freed.  "This is by design" was suppose to refer to
> requiring a custom policy for measuring keys.
> 
> For now, these two patches are queued in the next-integrity-testing
> branch, but I would appreciate your addressing not freeing the memory
> associated with the keys, if a custom policy is not loaded.
> 
> Please note that I truncated the 2/2 patch description, as it repeats
> the existing verification example in commit ("2b60c0ecedf8 IMA: Read
> keyrings= option from the IMA policy").
> 
> thanks,
> 
> Mimi
> 

Sure - I am fine with truncating the 2/2 patch description. Thanks for 
doing that.

Regarding "Freeing the queued keys if custom policy is not loaded":

Shall I create a new patch set to address that and have that be reviewed 
independent of this patch set?

Like you'd suggested earlier, we can wait for a certain time, after IMA 
is initialized, and free the queue if a custom policy was not loaded.

Please let me know.

thanks,
  -lakshmi

Re: [PATCH v5 0/2] IMA: Deferred measurement of keys

[Mimi Zohar]

On Fri, 2019-12-20 at 11:25 -0800, Lakshmi Ramasubramanian wrote:
> On 12/20/2019 11:01 AM, Mimi Zohar wrote:
> 
> Hi Mimi,
> 
> >> If the kernel is built with both CONFIG_IMA and
> >> CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE enabled then the IMA policy
> >> must be applied as a custom policy. Not providing a custom policy
> >> in the above configuration would result in asymmeteric keys being queued
> >> until a custom policy is loaded. This is by design.
> > 
> > I didn't notice the "This is by design" here, referring to the memory
> > never being freed.  "This is by design" was suppose to refer to
> > requiring a custom policy for measuring keys.
> > 
> > For now, these two patches are queued in the next-integrity-testing
> > branch, but I would appreciate your addressing not freeing the memory
> > associated with the keys, if a custom policy is not loaded.
> > 
> > Please note that I truncated the 2/2 patch description, as it repeats
> > the existing verification example in commit ("2b60c0ecedf8 IMA: Read
> > keyrings= option from the IMA policy").
> > 
> > thanks,
> > 
> > Mimi
> > 
> 
> Sure - I am fine with truncating the 2/2 patch description. Thanks for 
> doing that.
> 
> Regarding "Freeing the queued keys if custom policy is not loaded":
> 
> Shall I create a new patch set to address that and have that be reviewed 
> independent of this patch set?

If it is just a single additional patch, feel free to post it without
a cover letter.

> 
> Like you'd suggested earlier, we can wait for a certain time, after IMA 
> is initialized, and free the queue if a custom policy was not loaded.

Different types of systems vary in boot time, but perhaps a certain
amount of time after IMA is initialized would be consistent.  This
would need to work for IoT devices/sensors to servers.

Mimi 

Re: [PATCH v5 0/2] IMA: Deferred measurement of keys

[Lakshmi Ramasubramanian]

On 12/20/19 11:36 AM, Mimi Zohar wrote:

>>
>> Shall I create a new patch set to address that and have that be reviewed
>> independent of this patch set?
> 
> If it is just a single additional patch, feel free to post it without
> a cover letter.

Sure

>>
>> Like you'd suggested earlier, we can wait for a certain time, after IMA
>> is initialized, and free the queue if a custom policy was not loaded.
> 
> Different types of systems vary in boot time, but perhaps a certain
> amount of time after IMA is initialized would be consistent.  This
> would need to work for IoT devices/sensors to servers.
> 
> Mimi
> 

Yes - I agree.

thanks,
  -lakshmi