RFC evm: digital signature extension

From: Dmitry Kasatkin <[email protected]>

This patchset introduces digital signature extensions for the IMA/EVM kernel integrity subsystem and is applied on the top of the EVM patches posted to LSM mailing list earlier.

Currently EVM stores the HMAC in security.evm to verify integrity of the file's metadata. This is quite sufficient for individually installed systems, where a system unique HMAC key can be provisioned and the initial filesystem labeling can be done.

Software installation for consumer electronics or embedded devices is usually done via flashing a filesystem image. Initial filesystem image labeling is done during image creation process. It either has to be done (1) using a system unique HMAC key or (2) using an image specific HMAC key. In first case, those keys are either unknown, or a unique image has to be created for thousand or millions of devices, which is not feasible. The second case, using an image specific HMAC key, would require (2.1) provisioning of the key to millions of devices, which is not easily feasible or (2.1) encrypting the key with a shared symmetric key which is not a strong security measure.

Digital signature extension for EVM provides a solution to perform labeling of the image using a single digital private key and use a known public key to verify the signature. For performance reasons, after verification, signature is replaced with local HMAC.

Digital signature verification uses RSA algorithm, implemented using cut-down port of multi-precision integers (MPI) library from GnuPG and has been taken from RedHat Enterprise Linux kernel (MODSIGN patches). Decision to use this library was made, because its performance was 2 times better than other ports such as libtommath library.

This is not related to these patches specifically, but gives some motivation for integrity protection in general. As runtime protection is ensured via access control mechanisms, the main purpose of integrity protection is to protect against offline modifications. Some people argue that protection against offline modifications is seen as locking down device against themselves. But that is not completely true. Yes, it might prevent the user from changing the functionality of the device, which might be seen as evil. But on other hand, the owner of the device, such as companies or operators, not the user of the device, might not like their devices being modified.

But the more important reason for integrity protection is protecting the users’ or owners’ from selling or giving them modified devices, which can do nasty things such as spying or stealing personal data. Integrity protection ensures that modifications of the system will not remain undetected.

There is also a second patchset which implements digital signature support for IMA-appraisal patchset, which is planned to be reviewed right after the IMA-appaisal review.

All patches on the top of ima-2.6 kernel are available here:
http://meego.gitorious.org/meego-platform-security/ima-ksign

Supporting utility for key handling and signing is available here:
http://meego.gitorious.org/meego-platform-security/evm-utils

Regards,
Dmitry

Dmitry Kasatkin (5):
crypto: GnuPG based MPI lib
crypto: ksign - digital signature verification support
evm: digital signature support
ksign: provides keyring to search in for the key
evm: creates dedicated evm keyring to store public keys

 crypto/Kconfig                      |   19 +
 crypto/Makefile                     |    4 +
 crypto/ksign.c                      |  270 +++++++
 crypto/mpi/Makefile                 |   30 +
 crypto/mpi/generic_mpi-asm-defs.h   |   10 +
 crypto/mpi/generic_mpih-add1.c      |   62 ++
 crypto/mpi/generic_mpih-lshift.c    |   66 ++
 crypto/mpi/generic_mpih-mul1.c      |   58 ++
 crypto/mpi/generic_mpih-mul2.c      |   63 ++
 crypto/mpi/generic_mpih-mul3.c      |   64 ++
 crypto/mpi/generic_mpih-rshift.c    |   65 ++
 crypto/mpi/generic_mpih-sub1.c      |   62 ++
 crypto/mpi/generic_udiv-w-sdiv.c    |  130 +++
 crypto/mpi/longlong.h               | 1502 +++++++++++++++++++++++++++++++++++
 crypto/mpi/mpi-add.c                |  258 ++++++
 crypto/mpi/mpi-bit.c                |  245 ++++++
 crypto/mpi/mpi-cmp.c                |   71 ++
 crypto/mpi/mpi-div.c                |  345 ++++++++
 crypto/mpi/mpi-gcd.c                |   60 ++
 crypto/mpi/mpi-inline.c             |   33 +
 crypto/mpi/mpi-inline.h             |  128 +++
 crypto/mpi/mpi-internal.h           |  265 ++++++
 crypto/mpi/mpi-inv.c                |  148 ++++
 crypto/mpi/mpi-mpow.c               |  113 +++
 crypto/mpi/mpi-mul.c                |  202 +++++
 crypto/mpi/mpi-pow.c                |  312 ++++++++
 crypto/mpi/mpi-scan.c               |  129 +++
 crypto/mpi/mpicoder.c               |  359 +++++++++
 crypto/mpi/mpih-cmp.c               |   58 ++
 crypto/mpi/mpih-div.c               |  534 +++++++++++++
 crypto/mpi/mpih-mul.c               |  546 +++++++++++++
 crypto/mpi/mpiutil.c                |  213 +++++
 include/linux/crypto/ksign.h        |   48 ++
 include/linux/crypto/mpi.h          |  147 ++++
 security/integrity/evm/Kconfig      |   14 +
 security/integrity/evm/evm.h        |   33 +
 security/integrity/evm/evm_crypto.c |   66 ++-
 security/integrity/evm/evm_main.c   |   83 ++-
 38 files changed, 6783 insertions(+), 32 deletions(-)
 create mode 100644 crypto/ksign.c
 create mode 100644 crypto/mpi/Makefile
 create mode 100644 crypto/mpi/generic_mpi-asm-defs.h
 create mode 100644 crypto/mpi/generic_mpih-add1.c
 create mode 100644 crypto/mpi/generic_mpih-lshift.c
 create mode 100644 crypto/mpi/generic_mpih-mul1.c
 create mode 100644 crypto/mpi/generic_mpih-mul2.c
 create mode 100644 crypto/mpi/generic_mpih-mul3.c
 create mode 100644 crypto/mpi/generic_mpih-rshift.c
 create mode 100644 crypto/mpi/generic_mpih-sub1.c
 create mode 100644 crypto/mpi/generic_udiv-w-sdiv.c
 create mode 100644 crypto/mpi/longlong.h
 create mode 100644 crypto/mpi/mpi-add.c
 create mode 100644 crypto/mpi/mpi-bit.c
 create mode 100644 crypto/mpi/mpi-cmp.c
 create mode 100644 crypto/mpi/mpi-div.c
 create mode 100644 crypto/mpi/mpi-gcd.c
 create mode 100644 crypto/mpi/mpi-inline.c
 create mode 100644 crypto/mpi/mpi-inline.h
 create mode 100644 crypto/mpi/mpi-internal.h
 create mode 100644 crypto/mpi/mpi-inv.c
 create mode 100644 crypto/mpi/mpi-mpow.c
 create mode 100644 crypto/mpi/mpi-mul.c
 create mode 100644 crypto/mpi/mpi-pow.c
 create mode 100644 crypto/mpi/mpi-scan.c
 create mode 100644 crypto/mpi/mpicoder.c
 create mode 100644 crypto/mpi/mpih-cmp.c
 create mode 100644 crypto/mpi/mpih-div.c
 create mode 100644 crypto/mpi/mpih-mul.c
 create mode 100644 crypto/mpi/mpiutil.c
 create mode 100644 include/linux/crypto/ksign.h
 create mode 100644 include/linux/crypto/mpi.h

1.7.4.1