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Commit d00a1c72 authored by Mimi Zohar's avatar Mimi Zohar Committed by James Morris
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keys: add new trusted key-type 



Define a new kernel key-type called 'trusted'.  Trusted keys are random
number symmetric keys, generated and RSA-sealed by the TPM.  The TPM
only unseals the keys, if the boot PCRs and other criteria match.
Userspace can only ever see encrypted blobs.

Based on suggestions by Jason Gunthorpe, several new options have been
added to support additional usages.

The new options are:
migratable=  designates that the key may/may not ever be updated
             (resealed under a new key, new pcrinfo or new auth.)

pcrlock=n    extends the designated PCR 'n' with a random value,
             so that a key sealed to that PCR may not be unsealed
             again until after a reboot.

keyhandle=   specifies the sealing/unsealing key handle.

keyauth=     specifies the sealing/unsealing key auth.

blobauth=    specifies the sealed data auth.

Implementation of a kernel reserved locality for trusted keys will be
investigated for a possible future extension.

Changelog:
- Updated and added examples to Documentation/keys-trusted-encrypted.txt
- Moved generic TPM constants to include/linux/tpm_command.h
  (David Howell's suggestion.)
- trusted_defined.c: replaced kzalloc with kmalloc, added pcrlock failure
  error handling, added const qualifiers where appropriate.
- moved to late_initcall
- updated from hash to shash (suggestion by David Howells)
- reduced worst stack usage (tpm_seal) from 530 to 312 bytes
- moved documentation to Documentation directory (suggestion by David Howells)
- all the other code cleanups suggested by David Howells
- Add pcrlock CAP_SYS_ADMIN dependency (based on comment by Jason Gunthorpe)
- New options: migratable, pcrlock, keyhandle, keyauth, blobauth (based on
  discussions with Jason Gunthorpe)
- Free payload on failure to create key(reported/fixed by Roberto Sassu)
- Updated Kconfig and other descriptions (based on Serge Hallyn's suggestion)
- Replaced kzalloc() with kmalloc() (reported by Serge Hallyn)

Signed-off-by: default avatarDavid Safford <safford@watson.ibm.com>
Signed-off-by: default avatarMimi Zohar <zohar@us.ibm.com>
Signed-off-by: default avatarJames Morris <jmorris@namei.org>
parent c749ba91

Documentation/keys-trusted-encrypted.txt

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			Trusted and Encrypted Keys



Trusted and Encrypted Keys are two new key types added to the existing kernel

key ring service.  Both of these new types are variable length symmetic keys,

and in both cases all keys are created in the kernel, and user space sees,

stores, and loads only encrypted blobs.  Trusted Keys require the availability

of a Trusted Platform Module (TPM) chip for greater security, while Encrypted

Keys can be used on any system.  All user level blobs, are displayed and loaded

in hex ascii for convenience, and are integrity verified.



Trusted Keys use a TPM both to generate and to seal the keys.  Keys are sealed

under a 2048 bit RSA key in the TPM, and optionally sealed to specified PCR

(integrity measurement) values, and only unsealed by the TPM, if PCRs and blob

integrity verifications match.  A loaded Trusted Key can be updated with new

(future) PCR values, so keys are easily migrated to new pcr values, such as

when the kernel and initramfs are updated.  The same key can have many saved

blobs under different PCR values, so multiple boots are easily supported.



By default, trusted keys are sealed under the SRK, which has the default

authorization value (20 zeros).  This can be set at takeownership time with the

trouser's utility: "tpm_takeownership -u -z".



Usage:

    keyctl add trusted name "new keylen [options]" ring

    keyctl add trusted name "load hex_blob [pcrlock=pcrnum]" ring

    keyctl update key "update [options]"

    keyctl print keyid



    options:

       keyhandle= ascii hex value of sealing key default 0x40000000 (SRK)

       keyauth=	  ascii hex auth for sealing key default 0x00...i

		  (40 ascii zeros)

       blobauth=  ascii hex auth for sealed data default 0x00...

		  (40 ascii zeros)

       blobauth=  ascii hex auth for sealed data default 0x00...

		  (40 ascii zeros)

       pcrinfo=	  ascii hex of PCR_INFO or PCR_INFO_LONG (no default)

       pcrlock=	  pcr number to be extended to "lock" blob

       migratable= 0|1 indicating permission to reseal to new PCR values,

                   default 1 (resealing allowed)



"keyctl print" returns an ascii hex copy of the sealed key, which is in standard

TPM_STORED_DATA format.  The key length for new keys are always in bytes.

Trusted Keys can be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit

within the 2048 bit SRK (RSA) keylength, with all necessary structure/padding.



Encrypted keys do not depend on a TPM, and are faster, as they use AES for

encryption/decryption.  New keys are created from kernel generated random

numbers, and are encrypted/decrypted using a specified 'master' key.  The

'master' key can either be a trusted-key or user-key type.  The main

disadvantage of encrypted keys is that if they are not rooted in a trusted key,

they are only as secure as the user key encrypting them.  The master user key

should therefore be loaded in as secure a way as possible, preferably early in

boot.



Usage:

  keyctl add encrypted name "new key-type:master-key-name keylen" ring

  keyctl add encrypted name "load hex_blob" ring

  keyctl update keyid "update key-type:master-key-name"



where 'key-type' is either 'trusted' or 'user'.



Examples of trusted and encrypted key usage:



Create and save a trusted key named "kmk" of length 32 bytes:



    $ keyctl add trusted kmk "new 32" @u

    440502848



    $ keyctl show

    Session Keyring

           -3 --alswrv    500   500  keyring: _ses

     97833714 --alswrv    500    -1   \_ keyring: _uid.500

    440502848 --alswrv    500   500       \_ trusted: kmk



    $ keyctl print 440502848

    0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915

    3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b

    27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722

    a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec

    d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d

    dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0

    f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b

    e4a8aea2b607ec96931e6f4d4fe563ba



    $ keyctl pipe 440502848 > kmk.blob



Load a trusted key from the saved blob:



    $ keyctl add trusted kmk "load `cat kmk.blob`" @u

    268728824



    $ keyctl print 268728824

    0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915

    3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b

    27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722

    a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec

    d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d

    dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0

    f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b

    e4a8aea2b607ec96931e6f4d4fe563ba



Reseal a trusted key under new pcr values:



    $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"

    $ keyctl print 268728824

    010100000000002c0002800093c35a09b70fff26e7a98ae786c641e678ec6ffb6b46d805

    77c8a6377aed9d3219c6dfec4b23ffe3000001005d37d472ac8a44023fbb3d18583a4f73

    d3a076c0858f6f1dcaa39ea0f119911ff03f5406df4f7f27f41da8d7194f45c9f4e00f2e

    df449f266253aa3f52e55c53de147773e00f0f9aca86c64d94c95382265968c354c5eab4

    9638c5ae99c89de1e0997242edfb0b501744e11ff9762dfd951cffd93227cc513384e7e6

    e782c29435c7ec2edafaa2f4c1fe6e7a781b59549ff5296371b42133777dcc5b8b971610

    94bc67ede19e43ddb9dc2baacad374a36feaf0314d700af0a65c164b7082401740e489c9

    7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef

    df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8



Create and save an encrypted key "evm" using the above trusted key "kmk":



    $ keyctl add encrypted evm "new trusted:kmk 32" @u

    159771175



    $ keyctl print 159771175

    trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382dbbc55

    be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e024717c64

    5972dcb82ab2dde83376d82b2e3c09ffc



    $ keyctl pipe 159771175 > evm.blob



Load an encrypted key "evm" from saved blob:



    $ keyctl add encrypted evm "load `cat evm.blob`" @u

    831684262



    $ keyctl print 831684262

    trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382dbbc55

    be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e024717c64

    5972dcb82ab2dde83376d82b2e3c09ffc





The initial consumer of trusted keys is EVM, which at boot time needs a high

quality symmetric key for HMAC protection of file metadata.  The use of a

trusted key provides strong guarantees that the EVM key has not been

compromised by a user level problem, and when sealed to specific boot PCR

values, protects against boot and offline attacks.  Other uses for trusted and

encrypted keys, such as for disk and file encryption are anticipated.

include/keys/trusted-type.h

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/*

 * Copyright (C) 2010 IBM Corporation

 * Author: David Safford <safford@us.ibm.com>

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation, version 2 of the License.

 */



#ifndef _KEYS_TRUSTED_TYPE_H

#define _KEYS_TRUSTED_TYPE_H



#include <linux/key.h>

#include <linux/rcupdate.h>



#define MIN_KEY_SIZE			32

#define MAX_KEY_SIZE			128

#define MAX_BLOB_SIZE			320



struct trusted_key_payload {

	struct rcu_head rcu;

	unsigned int key_len;

	unsigned int blob_len;

	unsigned char migratable;

	unsigned char key[MAX_KEY_SIZE + 1];

	unsigned char blob[MAX_BLOB_SIZE];

};



extern struct key_type key_type_trusted;



#endif /* _KEYS_TRUSTED_TYPE_H */

include/linux/tpm_command.h

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#ifndef __LINUX_TPM_COMMAND_H__

#define __LINUX_TPM_COMMAND_H__



/*

 * TPM Command constants from specifications at

 * http://www.trustedcomputinggroup.org

 */



/* Command TAGS */

#define TPM_TAG_RQU_COMMAND             193

#define TPM_TAG_RQU_AUTH1_COMMAND       194

#define TPM_TAG_RQU_AUTH2_COMMAND       195

#define TPM_TAG_RSP_COMMAND             196

#define TPM_TAG_RSP_AUTH1_COMMAND       197

#define TPM_TAG_RSP_AUTH2_COMMAND       198



/* Command Ordinals */

#define TPM_ORD_GETRANDOM               70

#define TPM_ORD_OSAP                    11

#define TPM_ORD_OIAP                    10

#define TPM_ORD_SEAL                    23

#define TPM_ORD_UNSEAL                  24



/* Other constants */

#define SRKHANDLE                       0x40000000

#define TPM_NONCE_SIZE                  20



#endif

security/Kconfig

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@@ -21,6 +21,21 @@ config KEYS 




	  If you are unsure as to whether this is required, answer N.

	  If you are unsure as to whether this is required, answer N.





config TRUSTED_KEYS

	tristate "TRUSTED KEYS"

	depends on KEYS && TCG_TPM

	select CRYPTO

	select CRYPTO_HMAC

	select CRYPTO_SHA1

	help

	  This option provides support for creating, sealing, and unsealing

	  keys in the kernel. Trusted keys are random number symmetric keys,

	  generated and RSA-sealed by the TPM. The TPM only unseals the keys,

	  if the boot PCRs and other criteria match.  Userspace will only ever

	  see encrypted blobs.



	  If you are unsure as to whether this is required, answer N.



config KEYS_DEBUG_PROC_KEYS

config KEYS_DEBUG_PROC_KEYS

	bool "Enable the /proc/keys file by which keys may be viewed"

	bool "Enable the /proc/keys file by which keys may be viewed"

	depends on KEYS

	depends on KEYS

security/keys/Makefile

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@@ -13,6 +13,7 @@ obj-y := \ 
	request_key_auth.o \

	request_key_auth.o \

	user_defined.o

	user_defined.o





obj-$(CONFIG_TRUSTED_KEYS) += trusted_defined.o

obj-$(CONFIG_KEYS_COMPAT) += compat.o

obj-$(CONFIG_KEYS_COMPAT) += compat.o

obj-$(CONFIG_PROC_FS) += proc.o

obj-$(CONFIG_PROC_FS) += proc.o

obj-$(CONFIG_SYSCTL) += sysctl.o
 
obj-$(CONFIG_SYSCTL) += sysctl.o