Merge branch 'next-evm-digsig' of... (4e2c5b28) · Commits · e / devices / android_kernel_fairphone_FP3

Documentation/digsig.txt

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		Digital Signature Verification API

		CONTENTS

		1. Introduction
		2. API
		3. User-space utilities


		1. Introduction

		Digital signature verification API provides a method to verify digital signature.
		Currently digital signatures are used by the IMA/EVM integrity protection subsystem.

		Digital signature verification is implemented using cut-down kernel port of
		GnuPG multi-precision integers (MPI) library. The kernel port provides
		memory allocation errors handling, has been refactored according to kernel
		coding style, and checkpatch.pl reported errors and warnings have been fixed.

		Public key and signature consist of header and MPIs.

		struct pubkey_hdr {
		uint8_t version; /* key format version */
		time_t timestamp; /* key made, always 0 for now */
		uint8_t algo;
		uint8_t nmpi;
		char mpi[0];
		} __packed;

		struct signature_hdr {
		uint8_t version; /* signature format version */
		time_t timestamp; /* signature made */
		uint8_t algo;
		uint8_t hash;
		uint8_t keyid[8];
		uint8_t nmpi;
		char mpi[0];
		} __packed;

		keyid equals to SHA1[12-19] over the total key content.
		Signature header is used as an input to generate a signature.
		Such approach insures that key or signature header could not be changed.
		It protects timestamp from been changed and can be used for rollback
		protection.

		2. API

		API currently includes only 1 function:

		digsig_verify() - digital signature verification with public key


		/**
		* digsig_verify() - digital signature verification with public key
		* @keyring: keyring to search key in
		* @sig: digital signature
		* @sigen: length of the signature
		* @data: data
		* @datalen: length of the data
		* @return: 0 on success, -EINVAL otherwise
		*
		* Verifies data integrity against digital signature.
		* Currently only RSA is supported.
		* Normally hash of the content is used as a data for this function.
		*
		*/
		int digsig_verify(struct key keyring, const char sig, int siglen,
		const char *data, int datalen);

		3. User-space utilities

		The signing and key management utilities evm-utils provide functionality
		to generate signatures, to load keys into the kernel keyring.
		Keys can be in PEM or converted to the kernel format.
		When the key is added to the kernel keyring, the keyid defines the name
		of the key: 5D2B05FC633EE3E8 in the example bellow.

		Here is example output of the keyctl utility.

		$ keyctl show
		Session Keyring
		-3 --alswrv 0 0 keyring: _ses
		603976250 --alswrv 0 -1 \_ keyring: _uid.0
		817777377 --alswrv 0 0 \_ user: kmk
		891974900 --alswrv 0 0 \_ encrypted: evm-key
		170323636 --alswrv 0 0 \_ keyring: _module
		548221616 --alswrv 0 0 \_ keyring: _ima
		128198054 --alswrv 0 0 \_ keyring: _evm

		$ keyctl list 128198054
		1 key in keyring:
		620789745: --alswrv 0 0 user: 5D2B05FC633EE3E8


		Dmitry Kasatkin
		06.10.2011

include/linux/digsig.h

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		/*
		* Copyright (C) 2011 Nokia Corporation
		* Copyright (C) 2011 Intel Corporation
		*
		* Author:
		* Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
		* <dmitry.kasatkin@intel.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 _DIGSIG_H
		#define _DIGSIG_H

		#include <linux/key.h>

		enum pubkey_algo {
		PUBKEY_ALGO_RSA,
		PUBKEY_ALGO_MAX,
		};

		enum digest_algo {
		DIGEST_ALGO_SHA1,
		DIGEST_ALGO_SHA256,
		DIGEST_ALGO_MAX
		};

		struct pubkey_hdr {
		uint8_t version; /* key format version */
		time_t timestamp; /* key made, always 0 for now */
		uint8_t algo;
		uint8_t nmpi;
		char mpi[0];
		} __packed;

		struct signature_hdr {
		uint8_t version; /* signature format version */
		time_t timestamp; /* signature made */
		uint8_t algo;
		uint8_t hash;
		uint8_t keyid[8];
		uint8_t nmpi;
		char mpi[0];
		} __packed;

		#if defined(CONFIG_DIGSIG) \|\| defined(CONFIG_DIGSIG_MODULE)

		int digsig_verify(struct key keyring, const char sig, int siglen,
		const char *digest, int digestlen);

		#else

		static inline int digsig_verify(struct key keyring, const char sig,
		int siglen, const char *digest, int digestlen)
		{
		return -EOPNOTSUPP;
		}

		#endif /* CONFIG_DIGSIG */

		#endif /* _DIGSIG_H */

include/linux/mpi.h

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		/* mpi.h - Multi Precision Integers
		* Copyright (C) 1994, 1996, 1998, 1999,
		* 2000, 2001 Free Software Foundation, Inc.
		*
		* This file is part of GNUPG.
		*
		* GNUPG 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; either version 2 of the License, or
		* (at your option) any later version.
		*
		* GNUPG is distributed in the hope that it will be useful,
		* but WITHOUT ANY WARRANTY; without even the implied warranty of
		* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
		* GNU General Public License for more details.
		*
		* You should have received a copy of the GNU General Public License
		* along with this program; if not, write to the Free Software
		* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
		*
		* Note: This code is heavily based on the GNU MP Library.
		* Actually it's the same code with only minor changes in the
		* way the data is stored; this is to support the abstraction
		* of an optional secure memory allocation which may be used
		* to avoid revealing of sensitive data due to paging etc.
		* The GNU MP Library itself is published under the LGPL;
		* however I decided to publish this code under the plain GPL.
		*/

		#ifndef G10_MPI_H
		#define G10_MPI_H

		#include <linux/types.h>

		/* DSI defines */

		#define SHA1_DIGEST_LENGTH 20

		/end of DSI defines /

		#define BYTES_PER_MPI_LIMB (BITS_PER_LONG / 8)
		#define BITS_PER_MPI_LIMB BITS_PER_LONG

		typedef unsigned long int mpi_limb_t;
		typedef signed long int mpi_limb_signed_t;

		struct gcry_mpi {
		int alloced; /* array size (# of allocated limbs) */
		int nlimbs; /* number of valid limbs */
		int nbits; /* the real number of valid bits (info only) */
		int sign; /* indicates a negative number */
		unsigned flags; /* bit 0: array must be allocated in secure memory space */
		/* bit 1: not used */
		/* bit 2: the limb is a pointer to some m_alloced data */
		mpi_limb_t d; / array with the limbs */
		};

		typedef struct gcry_mpi *MPI;

		#define MPI_NULL NULL

		#define mpi_get_nlimbs(a) ((a)->nlimbs)
		#define mpi_is_neg(a) ((a)->sign)

		/-- mpiutil.c --/
		MPI mpi_alloc(unsigned nlimbs);
		MPI mpi_alloc_secure(unsigned nlimbs);
		MPI mpi_alloc_like(MPI a);
		void mpi_free(MPI a);
		int mpi_resize(MPI a, unsigned nlimbs);
		int mpi_copy(MPI *copy, const MPI a);
		void mpi_clear(MPI a);
		int mpi_set(MPI w, MPI u);
		int mpi_set_ui(MPI w, ulong u);
		MPI mpi_alloc_set_ui(unsigned long u);
		void mpi_m_check(MPI a);
		void mpi_swap(MPI a, MPI b);

		/-- mpicoder.c --/
		MPI do_encode_md(const void *sha_buffer, unsigned nbits);
		MPI mpi_read_from_buffer(const void buffer, unsigned ret_nread);
		int mpi_fromstr(MPI val, const char *str);
		u32 mpi_get_keyid(MPI a, u32 *keyid);
		void mpi_get_buffer(MPI a, unsigned nbytes, int *sign);
		void mpi_get_secure_buffer(MPI a, unsigned nbytes, int *sign);
		int mpi_set_buffer(MPI a, const void *buffer, unsigned nbytes, int sign);

		#define log_mpidump g10_log_mpidump

		/-- mpi-add.c --/
		int mpi_add_ui(MPI w, MPI u, ulong v);
		int mpi_add(MPI w, MPI u, MPI v);
		int mpi_addm(MPI w, MPI u, MPI v, MPI m);
		int mpi_sub_ui(MPI w, MPI u, ulong v);
		int mpi_sub(MPI w, MPI u, MPI v);
		int mpi_subm(MPI w, MPI u, MPI v, MPI m);

		/-- mpi-mul.c --/
		int mpi_mul_ui(MPI w, MPI u, ulong v);
		int mpi_mul_2exp(MPI w, MPI u, ulong cnt);
		int mpi_mul(MPI w, MPI u, MPI v);
		int mpi_mulm(MPI w, MPI u, MPI v, MPI m);

		/-- mpi-div.c --/
		ulong mpi_fdiv_r_ui(MPI rem, MPI dividend, ulong divisor);
		int mpi_fdiv_r(MPI rem, MPI dividend, MPI divisor);
		int mpi_fdiv_q(MPI quot, MPI dividend, MPI divisor);
		int mpi_fdiv_qr(MPI quot, MPI rem, MPI dividend, MPI divisor);
		int mpi_tdiv_r(MPI rem, MPI num, MPI den);
		int mpi_tdiv_qr(MPI quot, MPI rem, MPI num, MPI den);
		int mpi_tdiv_q_2exp(MPI w, MPI u, unsigned count);
		int mpi_divisible_ui(const MPI dividend, ulong divisor);

		/-- mpi-gcd.c --/
		int mpi_gcd(MPI g, const MPI a, const MPI b);

		/-- mpi-pow.c --/
		int mpi_pow(MPI w, MPI u, MPI v);
		int mpi_powm(MPI res, MPI base, MPI exp, MPI mod);

		/-- mpi-mpow.c --/
		int mpi_mulpowm(MPI res, MPI basearray, MPI exparray, MPI mod);

		/-- mpi-cmp.c --/
		int mpi_cmp_ui(MPI u, ulong v);
		int mpi_cmp(MPI u, MPI v);

		/-- mpi-scan.c --/
		int mpi_getbyte(MPI a, unsigned idx);
		void mpi_putbyte(MPI a, unsigned idx, int value);
		unsigned mpi_trailing_zeros(MPI a);

		/-- mpi-bit.c --/
		void mpi_normalize(MPI a);
		unsigned mpi_get_nbits(MPI a);
		int mpi_test_bit(MPI a, unsigned n);
		int mpi_set_bit(MPI a, unsigned n);
		int mpi_set_highbit(MPI a, unsigned n);
		void mpi_clear_highbit(MPI a, unsigned n);
		void mpi_clear_bit(MPI a, unsigned n);
		int mpi_rshift(MPI x, MPI a, unsigned n);

		/-- mpi-inv.c --/
		int mpi_invm(MPI x, MPI u, MPI v);

		#endif /G10_MPI_H /

lib/Kconfig

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		@@ -276,4 +276,29 @@ config CORDIC
		so its calculations are in fixed point. Modules can select this
		when they require this function. Module will be called cordic.

		config MPILIB
		tristate "Multiprecision maths library"
		help
		Multiprecision maths library from GnuPG.
		It is used to implement RSA digital signature verification,
		which is used by IMA/EVM digital signature extension.

		config MPILIB_EXTRA
		bool "Multiprecision maths library - additional sources"
		depends on MPILIB
		help
		Multiprecision maths library from GnuPG.
		It is used to implement RSA digital signature verification,
		which is used by IMA/EVM digital signature extension.
		This code in unnecessary for RSA digital signature verification,
		and can be compiled if needed.

		config DIGSIG
		tristate "In-kernel signature checker"
		depends on CRYPTO
		select MPILIB
		help
		Digital signature verification. Currently only RSA is supported.
		Implementation is done using GnuPG MPI library

		endmenu

lib/Makefile

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		@@ -115,6 +115,9 @@ obj-$(CONFIG_CPU_RMAP) += cpu_rmap.o

		obj-$(CONFIG_CORDIC) += cordic.o

		obj-$(CONFIG_MPILIB) += mpi/
		obj-$(CONFIG_DIGSIG) += digsig.o

		hostprogs-y := gen_crc32table
		clean-files := crc32table.h