diff mbox series

[v7,8/8] selinux: include a consumer of the new IMA critical data hook

Message ID 20201209194212.5131-9-tusharsu@linux.microsoft.com (mailing list archive)
State New
Headers show
Series IMA: support for measuring kernel integrity critical data | expand

Commit Message

Tushar Sugandhi Dec. 9, 2020, 7:42 p.m. UTC
From: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>

IMA measures files and buffer data such as keys, command line arguments
passed to the kernel on kexec system call, etc. While these measurements
enable monitoring and validating the integrity of the system, it is not
sufficient. Various data structures, policies and states stored in kernel
memory also impact the integrity of the system. Updates to these data
structures would have an impact on the security functionalities.
For example, SELinux stores the active policy in memory. Changes to this
data at runtime would have an impact on the security guarantees provided
by SELinux. Measuring such in-memory data structures through IMA
subsystem provides a secure way for a remote attestation service to
know the state of the system and also the runtime changes in the state
of the system.

SELinux policy is a critical data for this security module that needs
to be measured. This measurement can be used by an attestation service,
for instance, to verify if the policy has been setup correctly and that
it hasn't been tampered at run-time.

Measure the hash of the loaded policy by calling the IMA hook
ima_measure_critical_data(). Since the size of the loaded policy can
be large (several MB), measure the hash of the policy instead of
the entire policy to avoid bloating the IMA log entry.

Add "selinux" to the list of supported data sources maintained by IMA
to enable measuring SELinux data.

To enable SELinux data measurement, the following steps are required:

1, Add "ima_policy=critical_data" to the kernel command line arguments
   to enable measuring SELinux data at boot time.
For example,
  BOOT_IMAGE=/boot/vmlinuz-5.10.0-rc1+ root=UUID=fd643309-a5d2-4ed3-b10d-3c579a5fab2f ro nomodeset security=selinux ima_policy=critical_data

2, Add the following rule to /etc/ima/ima-policy
   measure func=CRITICAL_DATA data_source=selinux

Sample measurement of the hash of SELinux policy:

To verify the measured data with the current SELinux policy run
the following commands and verify the output hash values match.

  sha256sum /sys/fs/selinux/policy | cut -d' ' -f 1

  grep "selinux-policy-hash" /sys/kernel/security/integrity/ima/ascii_runtime_measurements | tail -1 | cut -d' ' -f 6

Note that the actual verification of SELinux policy would require loading
the expected policy into an identical kernel on a pristine/known-safe
system and run the sha256sum /sys/kernel/selinux/policy there to get
the expected hash.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com>
---
 Documentation/ABI/testing/ima_policy |  3 +-
 security/selinux/Makefile            |  2 +
 security/selinux/include/security.h  | 11 +++-
 security/selinux/measure.c           | 86 ++++++++++++++++++++++++++++
 security/selinux/ss/services.c       | 71 ++++++++++++++++++++---
 5 files changed, 162 insertions(+), 11 deletions(-)
 create mode 100644 security/selinux/measure.c

Comments

Tyler Hicks Dec. 11, 2020, 3:36 p.m. UTC | #1
On 2020-12-09 11:42:12, Tushar Sugandhi wrote:
> From: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
> 
> IMA measures files and buffer data such as keys, command line arguments
> passed to the kernel on kexec system call, etc. While these measurements
> enable monitoring and validating the integrity of the system, it is not
> sufficient. Various data structures, policies and states stored in kernel
> memory also impact the integrity of the system. Updates to these data
> structures would have an impact on the security functionalities.

This is repetitive when looking at the entire series. I think it can be
dropped.

> For example, SELinux stores the active policy in memory. Changes to this

Start here and drop the "For example, ":

 SELinux stores the active policy in memory and changes to this data ...

> data at runtime would have an impact on the security guarantees provided
> by SELinux. Measuring such in-memory data structures through IMA
> subsystem provides a secure way for a remote attestation service to
> know the state of the system and also the runtime changes in the state
> of the system.
> 
> SELinux policy is a critical data for this security module that needs

 SELinux policy is critical data and should be measured. This measurement ...

> to be measured. This measurement can be used by an attestation service,
> for instance, to verify if the policy has been setup correctly and that
> it hasn't been tampered at run-time.
> 
> Measure the hash of the loaded policy by calling the IMA hook
> ima_measure_critical_data(). Since the size of the loaded policy can
> be large (several MB), measure the hash of the policy instead of
> the entire policy to avoid bloating the IMA log entry.
> 
> Add "selinux" to the list of supported data sources maintained by IMA
> to enable measuring SELinux data.
> 
> To enable SELinux data measurement, the following steps are required:
> 
> 1, Add "ima_policy=critical_data" to the kernel command line arguments
>    to enable measuring SELinux data at boot time.
> For example,
>   BOOT_IMAGE=/boot/vmlinuz-5.10.0-rc1+ root=UUID=fd643309-a5d2-4ed3-b10d-3c579a5fab2f ro nomodeset security=selinux ima_policy=critical_data
> 
> 2, Add the following rule to /etc/ima/ima-policy
>    measure func=CRITICAL_DATA data_source=selinux
> 
> Sample measurement of the hash of SELinux policy:
> 
> To verify the measured data with the current SELinux policy run
> the following commands and verify the output hash values match.
> 
>   sha256sum /sys/fs/selinux/policy | cut -d' ' -f 1
> 
>   grep "selinux-policy-hash" /sys/kernel/security/integrity/ima/ascii_runtime_measurements | tail -1 | cut -d' ' -f 6
> 
> Note that the actual verification of SELinux policy would require loading
> the expected policy into an identical kernel on a pristine/known-safe
> system and run the sha256sum /sys/kernel/selinux/policy there to get
> the expected hash.
> 
> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
> Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com>
> ---
>  Documentation/ABI/testing/ima_policy |  3 +-
>  security/selinux/Makefile            |  2 +
>  security/selinux/include/security.h  | 11 +++-
>  security/selinux/measure.c           | 86 ++++++++++++++++++++++++++++
>  security/selinux/ss/services.c       | 71 ++++++++++++++++++++---
>  5 files changed, 162 insertions(+), 11 deletions(-)
>  create mode 100644 security/selinux/measure.c
> 
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index 0f4ee9e0a455..7c7023f7986b 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -52,8 +52,9 @@ Description:
>  			template:= name of a defined IMA template type
>  			(eg, ima-ng). Only valid when action is "measure".
>  			pcr:= decimal value
> -			data_source:= [label]
> +			data_source:= [selinux]|[label]
>  			label:= a unique string used for grouping and limiting critical data.
> +			For example, "selinux" to measure critical data for SELinux.
>  
>  		  default policy:
>  			# PROC_SUPER_MAGIC
> diff --git a/security/selinux/Makefile b/security/selinux/Makefile
> index 4d8e0e8adf0b..83d512116341 100644
> --- a/security/selinux/Makefile
> +++ b/security/selinux/Makefile
> @@ -16,6 +16,8 @@ selinux-$(CONFIG_NETLABEL) += netlabel.o
>  
>  selinux-$(CONFIG_SECURITY_INFINIBAND) += ibpkey.o
>  
> +selinux-$(CONFIG_IMA) += measure.o
> +
>  ccflags-y := -I$(srctree)/security/selinux -I$(srctree)/security/selinux/include
>  
>  $(addprefix $(obj)/,$(selinux-y)): $(obj)/flask.h
> diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
> index 3cc8bab31ea8..18ee65c98446 100644
> --- a/security/selinux/include/security.h
> +++ b/security/selinux/include/security.h
> @@ -229,7 +229,8 @@ void selinux_policy_cancel(struct selinux_state *state,
>  			struct selinux_policy *policy);
>  int security_read_policy(struct selinux_state *state,
>  			 void **data, size_t *len);
> -
> +int security_read_policy_kernel(struct selinux_state *state,
> +				void **data, size_t *len);
>  int security_policycap_supported(struct selinux_state *state,
>  				 unsigned int req_cap);
>  
> @@ -446,4 +447,12 @@ extern void ebitmap_cache_init(void);
>  extern void hashtab_cache_init(void);
>  extern int security_sidtab_hash_stats(struct selinux_state *state, char *page);
>  
> +#ifdef CONFIG_IMA
> +extern void selinux_measure_state(struct selinux_state *selinux_state);
> +#else
> +static inline void selinux_measure_state(struct selinux_state *selinux_state)
> +{
> +}
> +#endif
> +
>  #endif /* _SELINUX_SECURITY_H_ */
> diff --git a/security/selinux/measure.c b/security/selinux/measure.c
> new file mode 100644
> index 000000000000..c409ada6ea39
> --- /dev/null
> +++ b/security/selinux/measure.c
> @@ -0,0 +1,86 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Measure SELinux state using IMA subsystem.
> + */
> +#include <linux/vmalloc.h>
> +#include <linux/ktime.h>
> +#include <linux/ima.h>
> +#include "security.h"
> +
> +/*
> + * This function creates a unique name by appending the timestamp to
> + * the given string. This string is passed as "event_name" to the IMA
> + * hook to measure the given SELinux data.
> + *
> + * The data provided by SELinux to the IMA subsystem for measuring may have
> + * already been measured (for instance the same state existed earlier).
> + * But for SELinux the current data represents a state change and hence
> + * needs to be measured again. To enable this, pass a unique "event_name"
> + * to the IMA hook so that IMA subsystem will always measure the given data.
> + *
> + * For example,
> + * At time T0 SELinux data to be measured is "foo". IMA measures it.
> + * At time T1 the data is changed to "bar". IMA measures it.
> + * At time T2 the data is changed to "foo" again. IMA will not measure it
> + * (since it was already measured) unless the event_name, for instance,
> + * is different in this call.
> + */
> +static char *selinux_event_name(const char *name_prefix)
> +{
> +	char *event_name = NULL;
> +	struct timespec64 cur_time;
> +
> +	ktime_get_real_ts64(&cur_time);
> +	event_name = kasprintf(GFP_KERNEL, "%s-%lld:%09ld", name_prefix,
> +			       cur_time.tv_sec, cur_time.tv_nsec);
> +	if (!event_name) {
> +		pr_err("%s: event name not allocated.\n", __func__);
> +		return NULL;
> +	}
> +
> +	return event_name;
> +}
> +
> +/*
> + * selinux_measure_state - Measure hash of the SELinux policy
> + *
> + * @state: selinux state struct
> + *
> + * NOTE: This function must be called with policy_mutex held.
> + */
> +void selinux_measure_state(struct selinux_state *state)
> +{
> +	void *policy = NULL;
> +	char *policy_event_name = NULL;
> +	size_t policy_len;
> +	int rc = 0;
> +	bool initialized = selinux_initialized(state);
> +
> +	/*
> +	 * Measure SELinux policy only after initialization is completed.
> +	 */
> +	if (!initialized)
> +		goto out;
> +
> +	policy_event_name = selinux_event_name("selinux-policy-hash");
> +	if (!policy_event_name) {
> +		pr_err("%s: Event name for policy not allocated.\n",
> +		       __func__);

If the kasprintf() in selinux_event_name() fails, we'll get two similar
error messages saying that the event name could not be allocated. One of
these error messages can be removed.

> +		rc = -ENOMEM;
> +		goto out;
> +	}
> +
> +	rc = security_read_policy_kernel(state, &policy, &policy_len);
> +	if (rc) {
> +		pr_err("%s: Failed to read policy %d.\n", __func__, rc);

The calls to pr_err() in this aren't quite following the style of the
other error SELinux error messages.

 $ git grep pr_err security/selinux
 security/selinux/hooks.c:               pr_err("SELinux:  out of range capability %d\n", cap);
 security/selinux/hooks.c:               pr_err("SELinux:  unable to map context to SID"
 security/selinux/netlink.c:     pr_err("SELinux:  OOM in %s\n", __func__);
 security/selinux/selinuxfs.c:   pr_err("SELinux:  Runtime disable is deprecated, use selinux=0 on the kernel cmdline.\n");
 security/selinux/selinuxfs.c:           pr_err("SELinux: failed to load policy booleans\n");
 security/selinux/selinuxfs.c:           pr_err("SELinux: failed to load policy classes\n");
 ...
 security/selinux/ss/services.c:         pr_err("SELinux: %s:  unrecognized SID %d\n",
 security/selinux/ss/services.c:         pr_err("SELinux: %s:  unrecognized SID %d\n",
 security/selinux/ss/services.c:         pr_err("SELinux: %s:  unrecognized SID %d\n",
 security/selinux/ss/services.c:         pr_err("SELinux: %s:  unrecognized SID %d\n",
 security/selinux/ss/services.c:         pr_err("SELinux: %s:  unrecognized class %s\n",

Prepending your error message strings with "SELinux: " and lowercasing the
first character after "%s: " ought to do it.


All the other code changes in this patch look correct to me.

Tyler


> +		goto out;
> +	}
> +
> +	ima_measure_critical_data("selinux", policy_event_name,
> +				  policy, policy_len, true);
> +
> +	vfree(policy);
> +
> +out:
> +	kfree(policy_event_name);
> +}
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index 9704c8a32303..dfa2e00894ae 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -2180,6 +2180,7 @@ static void selinux_notify_policy_change(struct selinux_state *state,
>  	selinux_status_update_policyload(state, seqno);
>  	selinux_netlbl_cache_invalidate();
>  	selinux_xfrm_notify_policyload();
> +	selinux_measure_state(state);
>  }
>  
>  void selinux_policy_commit(struct selinux_state *state,
> @@ -3875,8 +3876,33 @@ int security_netlbl_sid_to_secattr(struct selinux_state *state,
>  }
>  #endif /* CONFIG_NETLABEL */
>  
> +/**
> + * security_read_selinux_policy - read the policy.
> + * @policy: SELinux policy
> + * @data: binary policy data
> + * @len: length of data in bytes
> + *
> + */
> +static int security_read_selinux_policy(struct selinux_policy *policy,
> +					void *data, size_t *len)
> +{
> +	int rc;
> +	struct policy_file fp;
> +
> +	fp.data = data;
> +	fp.len = *len;
> +
> +	rc = policydb_write(&policy->policydb, &fp);
> +	if (rc)
> +		return rc;
> +
> +	*len = (unsigned long)fp.data - (unsigned long)data;
> +	return 0;
> +}
> +
>  /**
>   * security_read_policy - read the policy.
> + * @state: selinux_state
>   * @data: binary policy data
>   * @len: length of data in bytes
>   *
> @@ -3885,8 +3911,6 @@ int security_read_policy(struct selinux_state *state,
>  			 void **data, size_t *len)
>  {
>  	struct selinux_policy *policy;
> -	int rc;
> -	struct policy_file fp;
>  
>  	policy = rcu_dereference_protected(
>  			state->policy, lockdep_is_held(&state->policy_mutex));
> @@ -3898,14 +3922,43 @@ int security_read_policy(struct selinux_state *state,
>  	if (!*data)
>  		return -ENOMEM;
>  
> -	fp.data = *data;
> -	fp.len = *len;
> +	return security_read_selinux_policy(policy, *data, len);
> +}
>  
> -	rc = policydb_write(&policy->policydb, &fp);
> -	if (rc)
> -		return rc;
> +/**
> + * security_read_policy_kernel - read the policy.
> + * @state: selinux_state
> + * @data: binary policy data
> + * @len: length of data in bytes
> + *
> + * Allocates kernel memory for reading SELinux policy.
> + * This function is for internal use only and should not
> + * be used for returning data to user space.
> + *
> + * This function must be called with policy_mutex held.
> + */
> +int security_read_policy_kernel(struct selinux_state *state,
> +				void **data, size_t *len)
> +{
> +	struct selinux_policy *policy;
> +	int rc = 0;
>  
> -	*len = (unsigned long)fp.data - (unsigned long)*data;
> -	return 0;
> +	policy = rcu_dereference_protected(
> +			state->policy, lockdep_is_held(&state->policy_mutex));
> +	if (!policy) {
> +		rc = -EINVAL;
> +		goto out;
> +	}
> +
> +	*len = policy->policydb.len;
> +	*data = vmalloc(*len);
> +	if (!*data) {
> +		rc = -ENOMEM;
> +		goto out;
> +	}
>  
> +	rc = security_read_selinux_policy(policy, *data, len);
> +
> +out:
> +	return rc;
>  }
> -- 
> 2.17.1
>
Tyler Hicks Dec. 11, 2020, 3:41 p.m. UTC | #2
On 2020-12-11 09:36:30, Tyler Hicks wrote:
> The calls to pr_err() in this aren't quite following the style of the
> other error SELinux error messages.

Sorry, I left out a word. I meant to say that the calls to pr_err() in
this *file* aren't quite following the right style. Please adjust all of
them.

Thanks!

Tyler
Lakshmi Ramasubramanian Dec. 11, 2020, 4:27 p.m. UTC | #3
On 12/11/20 7:41 AM, Tyler Hicks wrote:
> On 2020-12-11 09:36:30, Tyler Hicks wrote:
>> The calls to pr_err() in this aren't quite following the style of the
>> other error SELinux error messages.
> 
> Sorry, I left out a word. I meant to say that the calls to pr_err() in
> this *file* aren't quite following the right style. Please adjust all of
> them.
> 
> Thanks!
> 

Thanks for reviewing the patch Tyler. I'll make the changes per your 
comments.

  -lakshmi
diff mbox series

Patch

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index 0f4ee9e0a455..7c7023f7986b 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -52,8 +52,9 @@  Description:
 			template:= name of a defined IMA template type
 			(eg, ima-ng). Only valid when action is "measure".
 			pcr:= decimal value
-			data_source:= [label]
+			data_source:= [selinux]|[label]
 			label:= a unique string used for grouping and limiting critical data.
+			For example, "selinux" to measure critical data for SELinux.
 
 		  default policy:
 			# PROC_SUPER_MAGIC
diff --git a/security/selinux/Makefile b/security/selinux/Makefile
index 4d8e0e8adf0b..83d512116341 100644
--- a/security/selinux/Makefile
+++ b/security/selinux/Makefile
@@ -16,6 +16,8 @@  selinux-$(CONFIG_NETLABEL) += netlabel.o
 
 selinux-$(CONFIG_SECURITY_INFINIBAND) += ibpkey.o
 
+selinux-$(CONFIG_IMA) += measure.o
+
 ccflags-y := -I$(srctree)/security/selinux -I$(srctree)/security/selinux/include
 
 $(addprefix $(obj)/,$(selinux-y)): $(obj)/flask.h
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index 3cc8bab31ea8..18ee65c98446 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -229,7 +229,8 @@  void selinux_policy_cancel(struct selinux_state *state,
 			struct selinux_policy *policy);
 int security_read_policy(struct selinux_state *state,
 			 void **data, size_t *len);
-
+int security_read_policy_kernel(struct selinux_state *state,
+				void **data, size_t *len);
 int security_policycap_supported(struct selinux_state *state,
 				 unsigned int req_cap);
 
@@ -446,4 +447,12 @@  extern void ebitmap_cache_init(void);
 extern void hashtab_cache_init(void);
 extern int security_sidtab_hash_stats(struct selinux_state *state, char *page);
 
+#ifdef CONFIG_IMA
+extern void selinux_measure_state(struct selinux_state *selinux_state);
+#else
+static inline void selinux_measure_state(struct selinux_state *selinux_state)
+{
+}
+#endif
+
 #endif /* _SELINUX_SECURITY_H_ */
diff --git a/security/selinux/measure.c b/security/selinux/measure.c
new file mode 100644
index 000000000000..c409ada6ea39
--- /dev/null
+++ b/security/selinux/measure.c
@@ -0,0 +1,86 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Measure SELinux state using IMA subsystem.
+ */
+#include <linux/vmalloc.h>
+#include <linux/ktime.h>
+#include <linux/ima.h>
+#include "security.h"
+
+/*
+ * This function creates a unique name by appending the timestamp to
+ * the given string. This string is passed as "event_name" to the IMA
+ * hook to measure the given SELinux data.
+ *
+ * The data provided by SELinux to the IMA subsystem for measuring may have
+ * already been measured (for instance the same state existed earlier).
+ * But for SELinux the current data represents a state change and hence
+ * needs to be measured again. To enable this, pass a unique "event_name"
+ * to the IMA hook so that IMA subsystem will always measure the given data.
+ *
+ * For example,
+ * At time T0 SELinux data to be measured is "foo". IMA measures it.
+ * At time T1 the data is changed to "bar". IMA measures it.
+ * At time T2 the data is changed to "foo" again. IMA will not measure it
+ * (since it was already measured) unless the event_name, for instance,
+ * is different in this call.
+ */
+static char *selinux_event_name(const char *name_prefix)
+{
+	char *event_name = NULL;
+	struct timespec64 cur_time;
+
+	ktime_get_real_ts64(&cur_time);
+	event_name = kasprintf(GFP_KERNEL, "%s-%lld:%09ld", name_prefix,
+			       cur_time.tv_sec, cur_time.tv_nsec);
+	if (!event_name) {
+		pr_err("%s: event name not allocated.\n", __func__);
+		return NULL;
+	}
+
+	return event_name;
+}
+
+/*
+ * selinux_measure_state - Measure hash of the SELinux policy
+ *
+ * @state: selinux state struct
+ *
+ * NOTE: This function must be called with policy_mutex held.
+ */
+void selinux_measure_state(struct selinux_state *state)
+{
+	void *policy = NULL;
+	char *policy_event_name = NULL;
+	size_t policy_len;
+	int rc = 0;
+	bool initialized = selinux_initialized(state);
+
+	/*
+	 * Measure SELinux policy only after initialization is completed.
+	 */
+	if (!initialized)
+		goto out;
+
+	policy_event_name = selinux_event_name("selinux-policy-hash");
+	if (!policy_event_name) {
+		pr_err("%s: Event name for policy not allocated.\n",
+		       __func__);
+		rc = -ENOMEM;
+		goto out;
+	}
+
+	rc = security_read_policy_kernel(state, &policy, &policy_len);
+	if (rc) {
+		pr_err("%s: Failed to read policy %d.\n", __func__, rc);
+		goto out;
+	}
+
+	ima_measure_critical_data("selinux", policy_event_name,
+				  policy, policy_len, true);
+
+	vfree(policy);
+
+out:
+	kfree(policy_event_name);
+}
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 9704c8a32303..dfa2e00894ae 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2180,6 +2180,7 @@  static void selinux_notify_policy_change(struct selinux_state *state,
 	selinux_status_update_policyload(state, seqno);
 	selinux_netlbl_cache_invalidate();
 	selinux_xfrm_notify_policyload();
+	selinux_measure_state(state);
 }
 
 void selinux_policy_commit(struct selinux_state *state,
@@ -3875,8 +3876,33 @@  int security_netlbl_sid_to_secattr(struct selinux_state *state,
 }
 #endif /* CONFIG_NETLABEL */
 
+/**
+ * security_read_selinux_policy - read the policy.
+ * @policy: SELinux policy
+ * @data: binary policy data
+ * @len: length of data in bytes
+ *
+ */
+static int security_read_selinux_policy(struct selinux_policy *policy,
+					void *data, size_t *len)
+{
+	int rc;
+	struct policy_file fp;
+
+	fp.data = data;
+	fp.len = *len;
+
+	rc = policydb_write(&policy->policydb, &fp);
+	if (rc)
+		return rc;
+
+	*len = (unsigned long)fp.data - (unsigned long)data;
+	return 0;
+}
+
 /**
  * security_read_policy - read the policy.
+ * @state: selinux_state
  * @data: binary policy data
  * @len: length of data in bytes
  *
@@ -3885,8 +3911,6 @@  int security_read_policy(struct selinux_state *state,
 			 void **data, size_t *len)
 {
 	struct selinux_policy *policy;
-	int rc;
-	struct policy_file fp;
 
 	policy = rcu_dereference_protected(
 			state->policy, lockdep_is_held(&state->policy_mutex));
@@ -3898,14 +3922,43 @@  int security_read_policy(struct selinux_state *state,
 	if (!*data)
 		return -ENOMEM;
 
-	fp.data = *data;
-	fp.len = *len;
+	return security_read_selinux_policy(policy, *data, len);
+}
 
-	rc = policydb_write(&policy->policydb, &fp);
-	if (rc)
-		return rc;
+/**
+ * security_read_policy_kernel - read the policy.
+ * @state: selinux_state
+ * @data: binary policy data
+ * @len: length of data in bytes
+ *
+ * Allocates kernel memory for reading SELinux policy.
+ * This function is for internal use only and should not
+ * be used for returning data to user space.
+ *
+ * This function must be called with policy_mutex held.
+ */
+int security_read_policy_kernel(struct selinux_state *state,
+				void **data, size_t *len)
+{
+	struct selinux_policy *policy;
+	int rc = 0;
 
-	*len = (unsigned long)fp.data - (unsigned long)*data;
-	return 0;
+	policy = rcu_dereference_protected(
+			state->policy, lockdep_is_held(&state->policy_mutex));
+	if (!policy) {
+		rc = -EINVAL;
+		goto out;
+	}
+
+	*len = policy->policydb.len;
+	*data = vmalloc(*len);
+	if (!*data) {
+		rc = -ENOMEM;
+		goto out;
+	}
 
+	rc = security_read_selinux_policy(policy, *data, len);
+
+out:
+	return rc;
 }