[RFC v1 0/5] evm: digital signature extension

[Dmitry Kasatkin]

From: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx>

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 usersâ
or ownersâ 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

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