mirror of
https://github.com/AsahiLinux/u-boot
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image: Add signing infrastructure
Add a structure to describe an algorithm which can sign and (later) verify images. Signed-off-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Glass
Tom Rini
parent
b5f3193734
commit
3e569a6b1e
6 changed files with 358 additions and 2 deletions
5
README
5
README
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@ -2805,6 +2805,11 @@ FIT uImage format:
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most specific compatibility entry of U-Boot's fdt's root node.
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The order of entries in the configuration's fdt is ignored.
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CONFIG_FIT_SIGNATURE
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This option enables signature verification of FIT uImages,
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using a hash signed and verified using RSA. See
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doc/uImage.FIT/signature.txt for more details.
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- Standalone program support:
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CONFIG_STANDALONE_LOAD_ADDR
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@ -243,6 +243,7 @@ COBJS-y += dlmalloc.o
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COBJS-y += image.o
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COBJS-$(CONFIG_OF_LIBFDT) += image-fdt.o
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COBJS-$(CONFIG_FIT) += image-fit.o
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COBJS-$(CONFIG_FIT_SIGNATURE) += image-sig.o
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COBJS-y += memsize.o
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COBJS-y += stdio.o
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42
common/image-sig.c
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42
common/image-sig.c
Normal file
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@ -0,0 +1,42 @@
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/*
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* Copyright (c) 2013, Google Inc.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of
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* the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
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* MA 02111-1307 USA
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*/
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#ifdef USE_HOSTCC
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#include "mkimage.h"
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#include <time.h>
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#else
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#include <common.h>
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#endif /* !USE_HOSTCC*/
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#include <errno.h>
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#include <image.h>
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struct image_sig_algo image_sig_algos[] = {
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};
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struct image_sig_algo *image_get_sig_algo(const char *name)
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{
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int i;
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for (i = 0; i < ARRAY_SIZE(image_sig_algos); i++) {
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if (!strcmp(image_sig_algos[i].name, name))
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return &image_sig_algos[i];
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}
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return NULL;
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}
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216
doc/uImage.FIT/signature.txt
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216
doc/uImage.FIT/signature.txt
Normal file
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@ -0,0 +1,216 @@
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U-Boot FIT Signature Verification
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=================================
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Introduction
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------------
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FIT supports hashing of images so that these hashes can be checked on
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loading. This protects against corruption of the image. However it does not
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prevent the substitution of one image for another.
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The signature feature allows the hash to be signed with a private key such
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that it can be verified using a public key later. Provided that the private
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key is kept secret and the public key is stored in a non-volatile place,
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any image can be verified in this way.
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See verified-boot.txt for more general information on verified boot.
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Concepts
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--------
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Some familiarity with public key cryptography is assumed in this section.
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The procedure for signing is as follows:
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- hash an image in the FIT
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- sign the hash with a private key to produce a signature
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- store the resulting signature in the FIT
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The procedure for verification is:
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- read the FIT
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- obtain the public key
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- extract the signature from the FIT
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- hash the image from the FIT
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- verify (with the public key) that the extracted signature matches the
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hash
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The signing is generally performed by mkimage, as part of making a firmware
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image for the device. The verification is normally done in U-Boot on the
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device.
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Algorithms
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----------
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In principle any suitable algorithm can be used to sign and verify a hash.
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At present only one class of algorithms is supported: SHA1 hashing with RSA.
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This works by hashing the image to produce a 20-byte hash.
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While it is acceptable to bring in large cryptographic libraries such as
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openssl on the host side (e.g. mkimage), it is not desirable for U-Boot.
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For the run-time verification side, it is important to keep code and data
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size as small as possible.
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For this reason the RSA image verification uses pre-processed public keys
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which can be used with a very small amount of code - just some extraction
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of data from the FDT and exponentiation mod n. Code size impact is a little
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under 5KB on Tegra Seaboard, for example.
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It is relatively straightforward to add new algorithms if required. If
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another RSA variant is needed, then it can be added to the table in
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image-sig.c. If another algorithm is needed (such as DSA) then it can be
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placed alongside rsa.c, and its functions added to the table in image-sig.c
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also.
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Creating an RSA key and certificate
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-----------------------------------
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To create a new public key, size 2048 bits:
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$ openssl genrsa -F4 -out keys/dev.key 2048
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To create a certificate for this:
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$ openssl req -batch -new -x509 -key keys/dev.key -out keys/dev.crt
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If you like you can look at the public key also:
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$ openssl rsa -in keys/dev.key -pubout
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Device Tree Bindings
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--------------------
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The following properties are required in the FIT's signature node(s) to
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allow thes signer to operate. These should be added to the .its file.
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Signature nodes sit at the same level as hash nodes and are called
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signature@1, signature@2, etc.
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- algo: Algorithm name (e.g. "sha1,rs2048")
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- key-name-hint: Name of key to use for signing. The keys will normally be in
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a single directory (parameter -k to mkimage). For a given key <name>, its
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private key is stored in <name>.key and the certificate is stored in
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<name>.crt.
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When the image is signed, the following properties are added (mandatory):
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- value: The signature data (e.g. 256 bytes for 2048-bit RSA)
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When the image is signed, the following properties are optional:
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- timestamp: Time when image was signed (standard Unix time_t format)
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- signer-name: Name of the signer (e.g. "mkimage")
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- signer-version: Version string of the signer (e.g. "2013.01")
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- comment: Additional information about the signer or image
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Example: See sign-images.its for an example image tree source file.
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Public Key Storage
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------------------
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In order to verify an image that has been signed with a public key we need to
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have a trusted public key. This cannot be stored in the signed image, since
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it would be easy to alter. For this implementation we choose to store the
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public key in U-Boot's control FDT (using CONFIG_OF_CONTROL).
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Public keys should be stored as sub-nodes in a /signature node. Required
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properties are:
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- algo: Algorithm name (e.g. "sha1,rs2048")
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Optional properties are:
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- key-name-hint: Name of key used for signing. This is only a hint since it
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is possible for the name to be changed. Verification can proceed by checking
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all available signing keys until one matches.
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- required: If present this indicates that the key must be verified for the
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image / configuration to be considered valid. Only required keys are
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normally verified by the FIT image booting algorithm. Valid values are
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"image" to force verification of all images, and "conf" to force verfication
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of the selected configuration (which then relies on hashes in the images to
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verify those).
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Each signing algorithm has its own additional properties.
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For RSA the following are mandatory:
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- rsa,num-bits: Number of key bits (e.g. 2048)
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- rsa,modulus: Modulus (N) as a big-endian multi-word integer
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- rsa,r-squared: (2^num-bits)^2 as a big-endian multi-word integer
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- rsa,n0-inverse: -1 / modulus[0] mod 2^32
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Verification
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------------
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FITs are verified when loaded. After the configuration is selected a list
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of required images is produced. If there are 'required' public keys, then
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each image must be verified against those keys. This means that every image
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that might be used by the target needs to be signed with 'required' keys.
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This happens automatically as part of a bootm command when FITs are used.
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Enabling FIT Verification
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-------------------------
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In addition to the options to enable FIT itself, the following CONFIGs must
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be enabled:
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CONFIG_FIT_SIGNATURE - enable signing and verfication in FITs
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CONFIG_RSA - enable RSA algorithm for signing
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Testing
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-------
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An easy way to test signing and verfication is to use the test script
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provided in test/vboot/vboot_test.sh. This uses sandbox (a special version
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of U-Boot which runs under Linux) to show the operation of a 'bootm'
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command loading and verifying images.
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A sample run is show below:
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$ make O=sandbox sandbox_config
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$ make O=sandbox
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$ O=sandbox ./test/vboot/vboot_test.sh
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Simple Verified Boot Test
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=========================
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Please see doc/uImage.FIT/verified-boot.txt for more information
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Build keys
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Build FIT with signed images
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Test Verified Boot Run: unsigned signatures:: OK
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Sign images
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Test Verified Boot Run: signed images: OK
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Build FIT with signed configuration
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Test Verified Boot Run: unsigned config: OK
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Sign images
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Test Verified Boot Run: signed config: OK
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Test passed
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Future Work
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-----------
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- Roll-back protection using a TPM is done using the tpm command. This can
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be scripted, but we might consider a default way of doing this, built into
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bootm.
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Possible Future Work
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--------------------
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- Add support for other RSA/SHA variants, such as rsa4096,sha512.
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- Other algorithms besides RSA
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- More sandbox tests for failure modes
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- Passwords for keys/certificates
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- Perhaps implement OAEP
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- Enhance bootm to permit scripted signature verification (so that a script
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can verify an image but not actually boot it)
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Simon Glass
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sjg@chromium.org
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1-1-13
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@ -46,6 +46,9 @@ struct lmb;
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#define CONFIG_OF_LIBFDT 1
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#define CONFIG_FIT_VERBOSE 1 /* enable fit_format_{error,warning}() */
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/* Support FIT image signing on host */
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#define CONFIG_FIT_SIGNATURE
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#define IMAGE_ENABLE_IGNORE 0
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#define IMAGE_INDENT_STRING ""
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@ -670,11 +673,12 @@ int image_setup_linux(bootm_headers_t *images);
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#define FIT_IMAGES_PATH "/images"
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#define FIT_CONFS_PATH "/configurations"
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/* hash node */
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/* hash/signature node */
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#define FIT_HASH_NODENAME "hash"
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#define FIT_ALGO_PROP "algo"
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#define FIT_VALUE_PROP "value"
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#define FIT_IGNORE_PROP "uboot-ignore"
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#define FIT_SIG_NODENAME "signature"
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/* image node */
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#define FIT_DATA_PROP "data"
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@ -804,15 +808,19 @@ int calculate_hash(const void *data, int data_len, const char *algo,
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uint8_t *value, int *value_len);
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/*
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* At present we only support verification on the device
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* At present we only support signing on the host, and verification on the
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* device
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*/
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#if defined(CONFIG_FIT_SIGNATURE)
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# ifdef USE_HOSTCC
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# define IMAGE_ENABLE_SIGN 1
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# define IMAGE_ENABLE_VERIFY 0
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#else
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# define IMAGE_ENABLE_SIGN 0
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# define IMAGE_ENABLE_VERIFY 1
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# endif
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#else
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# define IMAGE_ENABLE_SIGN 0
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# define IMAGE_ENABLE_VERIFY 0
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#endif
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@ -828,6 +836,84 @@ int calculate_hash(const void *data, int data_len, const char *algo,
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#define IMAGE_ENABLE_BEST_MATCH 0
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#endif
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/* Information passed to the signing routines */
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struct image_sign_info {
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const char *keydir; /* Directory conaining keys */
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const char *keyname; /* Name of key to use */
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void *fit; /* Pointer to FIT blob */
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int node_offset; /* Offset of signature node */
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struct image_sig_algo *algo; /* Algorithm information */
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const void *fdt_blob; /* FDT containing public keys */
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int required_keynode; /* Node offset of key to use: -1=any */
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const char *require_keys; /* Value for 'required' property */
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};
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/* A part of an image, used for hashing */
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struct image_region {
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const void *data;
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int size;
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};
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struct image_sig_algo {
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const char *name; /* Name of algorithm */
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/**
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* sign() - calculate and return signature for given input data
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*
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* @info: Specifies key and FIT information
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* @data: Pointer to the input data
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* @data_len: Data length
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* @sigp: Set to an allocated buffer holding the signature
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* @sig_len: Set to length of the calculated hash
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*
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* This computes input data signature according to selected algorithm.
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* Resulting signature value is placed in an allocated buffer, the
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* pointer is returned as *sigp. The length of the calculated
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* signature is returned via the sig_len pointer argument. The caller
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* should free *sigp.
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*
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* @return: 0, on success, -ve on error
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*/
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int (*sign)(struct image_sign_info *info,
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const struct image_region region[],
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int region_count, uint8_t **sigp, uint *sig_len);
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/**
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* add_verify_data() - Add verification information to FDT
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*
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* Add public key information to the FDT node, suitable for
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* verification at run-time. The information added depends on the
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* algorithm being used.
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*
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* @info: Specifies key and FIT information
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* @keydest: Destination FDT blob for public key data
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* @return: 0, on success, -ve on error
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*/
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int (*add_verify_data)(struct image_sign_info *info, void *keydest);
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/**
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* verify() - Verify a signature against some data
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*
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* @info: Specifies key and FIT information
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* @data: Pointer to the input data
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* @data_len: Data length
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* @sig: Signature
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* @sig_len: Number of bytes in signature
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* @return 0 if verified, -ve on error
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*/
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int (*verify)(struct image_sign_info *info,
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const struct image_region region[], int region_count,
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uint8_t *sig, uint sig_len);
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};
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/**
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* image_get_sig_algo() - Look up a signature algortihm
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*
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* @param name Name of algorithm
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* @return pointer to algorithm information, or NULL if not found
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*/
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struct image_sig_algo *image_get_sig_algo(const char *name);
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static inline int fit_image_check_target_arch(const void *fdt, int node)
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{
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return fit_image_check_arch(fdt, node, IH_ARCH_DEFAULT);
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@ -80,6 +80,7 @@ BIN_FILES-y += proftool(SFX)
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EXT_OBJ_FILES-$(CONFIG_BUILD_ENVCRC) += common/env_embedded.o
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EXT_OBJ_FILES-y += common/image.o
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EXT_OBJ_FILES-$(CONFIG_FIT) += common/image-fit.o
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EXT_OBJ_FILES-y += common/image-sig.o
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EXT_OBJ_FILES-y += lib/crc32.o
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EXT_OBJ_FILES-y += lib/md5.o
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EXT_OBJ_FILES-y += lib/sha1.o
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@ -154,6 +155,10 @@ HOSTSRCS += $(addprefix $(SRCTREE)/lib/libfdt/,$(LIBFDT_OBJ_FILES-y:.o=.c))
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BINS := $(addprefix $(obj),$(sort $(BIN_FILES-y)))
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LIBFDT_OBJS := $(addprefix $(obj),$(LIBFDT_OBJ_FILES-y))
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# We cannot check CONFIG_FIT_SIGNATURE here since it is not set on the host
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FIT_SIG_OBJ_FILES := image-sig.o
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FIT_SIG_OBJS := $(addprefix $(obj),$(FIT_SIG_OBJ_FILES))
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HOSTOBJS := $(addprefix $(obj),$(OBJ_FILES-y))
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NOPEDOBJS := $(addprefix $(obj),$(NOPED_OBJ_FILES-y))
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@ -213,6 +218,7 @@ $(obj)mkimage$(SFX): $(obj)aisimage.o \
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$(obj)image-fit.o \
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$(obj)image.o \
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$(obj)image-host.o \
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$(FIT_SIG_OBJS) \
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$(obj)imximage.o \
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$(obj)kwbimage.o \
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$(obj)pblimage.o \
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