[v6,2/3] IMA: Define an IMA hook to measure keys
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Message ID 20191113184658.2862-3-nramas@linux.microsoft.com
State New
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Series
  • KEYS: Measure keys when they are created or updated
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Commit Message

Lakshmi Ramasubramanian Nov. 13, 2019, 6:46 p.m. UTC
Measure asymmetric keys used for verifying file signatures,
certificates, etc.

This patch defines a new IMA hook namely ima_post_key_create_or_update()
to measure asymmetric keys.

Note that currently IMA subsystem can be enabled without
enabling KEYS subsystem.

Adding support for measuring asymmetric keys in IMA requires KEYS
subsystem to be enabled. To handle this dependency a new config
namely CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS has been added. Enabling
this config requires the following configs to be enabled:
    CONFIG_IMA, CONFIG_KEYS, CONFIG_ASYMMETRIC_KEY_TYPE, and
    CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE.

CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS is off by default.

The IMA hook is defined in a new file namely ima_asymmetric_keys.c
which is built only if CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS is enabled.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
---
 security/integrity/ima/Kconfig               | 14 ++++++
 security/integrity/ima/Makefile              |  1 +
 security/integrity/ima/ima_asymmetric_keys.c | 51 ++++++++++++++++++++
 3 files changed, 66 insertions(+)
 create mode 100644 security/integrity/ima/ima_asymmetric_keys.c

Comments

Mimi Zohar Nov. 13, 2019, 8:09 p.m. UTC | #1
On Wed, 2019-11-13 at 10:46 -0800, Lakshmi Ramasubramanian wrote:
> Measure asymmetric keys used for verifying file signatures,
> certificates, etc.
> 
> This patch defines a new IMA hook namely ima_post_key_create_or_update()
> to measure asymmetric keys.
> 
> Note that currently IMA subsystem can be enabled without
> enabling KEYS subsystem.
> 
> Adding support for measuring asymmetric keys in IMA requires KEYS
> subsystem to be enabled. To handle this dependency a new config
> namely CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS has been added. Enabling
> this config requires the following configs to be enabled:
>     CONFIG_IMA, CONFIG_KEYS, CONFIG_ASYMMETRIC_KEY_TYPE, and
>     CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE.
> 
> CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS is off by default.
> 
> The IMA hook is defined in a new file namely ima_asymmetric_keys.c
> which is built only if CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS is enabled.
> 
> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>

All that is is needed is the key and public_key structures, which are
defined in include/linux/keys.h and include/crypto/public_key.h.  If
the keys subsystem is disabled, then the new IMA hook won't be called.
 There's no need for a new Kconfig option or a new file.

Please move the hook to just after ima_kexec_cmdline().

Mimi

> ---
>  security/integrity/ima/Kconfig               | 14 ++++++
>  security/integrity/ima/Makefile              |  1 +
>  security/integrity/ima/ima_asymmetric_keys.c | 51 ++++++++++++++++++++
>  3 files changed, 66 insertions(+)
>  create mode 100644 security/integrity/ima/ima_asymmetric_keys.c
> 
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index 838476d780e5..c6d14884bc19 100644
> --- a/security/integrity/ima/Kconfig
> +++ b/security/integrity/ima/Kconfig
> @@ -310,3 +310,17 @@ config IMA_APPRAISE_SIGNED_INIT
>  	default n
>  	help
>  	   This option requires user-space init to be signed.
> +
> +config IMA_MEASURE_ASYMMETRIC_KEYS
> +	bool "Enable measuring asymmetric keys on key create or update"
> +	depends on IMA
> +	depends on KEYS
> +	depends on ASYMMETRIC_KEY_TYPE
> +	depends on ASYMMETRIC_PUBLIC_KEY_SUBTYPE
> +	default n
> +	help
> +	   This option enables measuring asymmetric keys when
> +	   the key is created or updated. Additionally, IMA policy
> +	   needs to be configured to either measure keys linked to
> +	   any keyring or only measure keys linked to the keyrings
> +	   specified in the IMA policy through the keyrings= option.
> diff --git a/security/integrity/ima/Makefile b/security/integrity/ima/Makefile
> index 31d57cdf2421..3e9d0ad68c7b 100644
> --- a/security/integrity/ima/Makefile
> +++ b/security/integrity/ima/Makefile
> @@ -12,3 +12,4 @@ ima-$(CONFIG_IMA_APPRAISE) += ima_appraise.o
>  ima-$(CONFIG_IMA_APPRAISE_MODSIG) += ima_modsig.o
>  ima-$(CONFIG_HAVE_IMA_KEXEC) += ima_kexec.o
>  obj-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o
> +obj-$(CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS) += ima_asymmetric_keys.o
> diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
> new file mode 100644
> index 000000000000..f6884641a622
> --- /dev/null
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -0,0 +1,51 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2019 Microsoft Corporation
> + *
> + * Author: Lakshmi Ramasubramanian (nramas@linux.microsoft.com)
> + *
> + * File: ima_asymmetric_keys.c
> + *       Defines an IMA hook to measure asymmetric keys on key
> + *       create or update.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <crypto/public_key.h>
> +#include <keys/asymmetric-type.h>
> +#include "ima.h"
> +
> +/**
> + * ima_post_key_create_or_update - measure asymmetric keys
> + * @keyring: keyring to which the key is linked to
> + * @key: created or updated key
> + * @flags: key flags
> + * @create: flag indicating whether the key was created or updated
> + *
> + * Keys can only be measured, not appraised.
> + */
> +void ima_post_key_create_or_update(struct key *keyring, struct key *key,
> +				   unsigned long flags, bool create)
> +{
> +	const struct public_key *pk;
> +
> +	/* Only asymmetric keys are handled by this hook. */
> +	if (key->type != &key_type_asymmetric)
> +		return;
> +
> +	/* Get the public_key of the given asymmetric key to measure. */
> +	pk = key->payload.data[asym_crypto];
> +
> +	/*
> +	 * keyring->description points to the name of the keyring
> +	 * (such as ".builtin_trusted_keys", ".ima", etc.) to
> +	 * which the given key is linked to.
> +	 *
> +	 * The name of the keyring is passed in the "eventname"
> +	 * parameter to process_buffer_measurement() and is set
> +	 * in the "eventname" field in ima_event_data for
> +	 * the key measurement IMA event.
> +	 */
> +	process_buffer_measurement(pk->key, pk->keylen,
> +				   keyring->description, KEY_CHECK, 0);
> +}
Lakshmi Ramasubramanian Nov. 13, 2019, 8:52 p.m. UTC | #2
On 11/13/19 12:09 PM, Mimi Zohar wrote:
>
> All that is is needed is the key and public_key structures, which are
> defined in include/linux/keys.h and include/crypto/public_key.h.  If
> the keys subsystem is disabled, then the new IMA hook won't be called.
>   There's no need for a new Kconfig option or a new file.
> 
> Please move the hook to just after ima_kexec_cmdline().
> 
> Mimi

Yes - IMA hook won't be called when KEYS subsystem is disabled.

But, build dependency is breaking since "struct key" is not defined 
without CONFIG_KEYS.

Sasha was able to craft a .config that enabled IMA without enabling KEYS 
and found the build break.

Please see the build output he'd shared.

***********************************************************************

In file included from security/integrity/ima/ima.h:25,
                 from security/integrity/ima/ima_fs.c:26:
./include/keys/asymmetric-type.h: In function ‘asymmetric_key_ids’:
./include/keys/asymmetric-type.h:72:12: error: dereferencing pointer to 
incomplete type ‘const struct key’
  return key->payload.data[asym_key_ids];
            ^~
make[3]: *** [scripts/Makefile.build:266: 
security/integrity/ima/ima_fs.o] Error 1
make[3]: *** Waiting for unfinished jobs....
In file included from security/integrity/ima/ima.h:25,
                 from security/integrity/ima/ima_queue.c:22:
./include/keys/asymmetric-type.h: In function ‘asymmetric_key_ids’:
./include/keys/asymmetric-type.h:72:12: error: dereferencing pointer to 
incomplete type ‘const struct key’
  return key->payload.data[asym_key_ids];

***********************************************************************

thanks,
  -lakshmi
Mimi Zohar Nov. 13, 2019, 9:18 p.m. UTC | #3
On Wed, 2019-11-13 at 12:52 -0800, Lakshmi Ramasubramanian wrote:
> On 11/13/19 12:09 PM, Mimi Zohar wrote:
> >
> > All that is is needed is the key and public_key structures, which are
> > defined in include/linux/keys.h and include/crypto/public_key.h.  If
> > the keys subsystem is disabled, then the new IMA hook won't be called.
> >   There's no need for a new Kconfig option or a new file.
> > 
> > Please move the hook to just after ima_kexec_cmdline().
> > 
> > Mimi
> 
> Yes - IMA hook won't be called when KEYS subsystem is disabled.
> 
> But, build dependency is breaking since "struct key" is not defined 
> without CONFIG_KEYS.
> 
> Sasha was able to craft a .config that enabled IMA without enabling KEYS 
> and found the build break.

Yes, thanks for pointing out the "#ifdef CONFIG_KEYS" in keys.h.  A
separate file is needed, as you pointed out, but still no need for a
new Kconfig.  The ima/Makefile can be based on CONFIG_KEYS.

Mimi
Lakshmi Ramasubramanian Nov. 13, 2019, 10:01 p.m. UTC | #4
On 11/13/19 1:18 PM, Mimi Zohar wrote:

> Yes, thanks for pointing out the "#ifdef CONFIG_KEYS" in keys.h.  A
> separate file is needed, as you pointed out, but still no need for a
> new Kconfig.  The ima/Makefile can be based on CONFIG_KEYS.
> 
> Mimi

Sure - i'll try it now and send an updated patch set.

thanks,
  -lakshmi

Patch
diff mbox series

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 838476d780e5..c6d14884bc19 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -310,3 +310,17 @@  config IMA_APPRAISE_SIGNED_INIT
 	default n
 	help
 	   This option requires user-space init to be signed.
+
+config IMA_MEASURE_ASYMMETRIC_KEYS
+	bool "Enable measuring asymmetric keys on key create or update"
+	depends on IMA
+	depends on KEYS
+	depends on ASYMMETRIC_KEY_TYPE
+	depends on ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	default n
+	help
+	   This option enables measuring asymmetric keys when
+	   the key is created or updated. Additionally, IMA policy
+	   needs to be configured to either measure keys linked to
+	   any keyring or only measure keys linked to the keyrings
+	   specified in the IMA policy through the keyrings= option.
diff --git a/security/integrity/ima/Makefile b/security/integrity/ima/Makefile
index 31d57cdf2421..3e9d0ad68c7b 100644
--- a/security/integrity/ima/Makefile
+++ b/security/integrity/ima/Makefile
@@ -12,3 +12,4 @@  ima-$(CONFIG_IMA_APPRAISE) += ima_appraise.o
 ima-$(CONFIG_IMA_APPRAISE_MODSIG) += ima_modsig.o
 ima-$(CONFIG_HAVE_IMA_KEXEC) += ima_kexec.o
 obj-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o
+obj-$(CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS) += ima_asymmetric_keys.o
diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
new file mode 100644
index 000000000000..f6884641a622
--- /dev/null
+++ b/security/integrity/ima/ima_asymmetric_keys.c
@@ -0,0 +1,51 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2019 Microsoft Corporation
+ *
+ * Author: Lakshmi Ramasubramanian (nramas@linux.microsoft.com)
+ *
+ * File: ima_asymmetric_keys.c
+ *       Defines an IMA hook to measure asymmetric keys on key
+ *       create or update.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <crypto/public_key.h>
+#include <keys/asymmetric-type.h>
+#include "ima.h"
+
+/**
+ * ima_post_key_create_or_update - measure asymmetric keys
+ * @keyring: keyring to which the key is linked to
+ * @key: created or updated key
+ * @flags: key flags
+ * @create: flag indicating whether the key was created or updated
+ *
+ * Keys can only be measured, not appraised.
+ */
+void ima_post_key_create_or_update(struct key *keyring, struct key *key,
+				   unsigned long flags, bool create)
+{
+	const struct public_key *pk;
+
+	/* Only asymmetric keys are handled by this hook. */
+	if (key->type != &key_type_asymmetric)
+		return;
+
+	/* Get the public_key of the given asymmetric key to measure. */
+	pk = key->payload.data[asym_crypto];
+
+	/*
+	 * keyring->description points to the name of the keyring
+	 * (such as ".builtin_trusted_keys", ".ima", etc.) to
+	 * which the given key is linked to.
+	 *
+	 * The name of the keyring is passed in the "eventname"
+	 * parameter to process_buffer_measurement() and is set
+	 * in the "eventname" field in ima_event_data for
+	 * the key measurement IMA event.
+	 */
+	process_buffer_measurement(pk->key, pk->keylen,
+				   keyring->description, KEY_CHECK, 0);
+}