[GIT PULL] Crypto keys and module signing

[GIT PULL] Crypto keys and module signing

[David Howells]

Hi James,

Could you pull my module signing code into the security tree?  The patches can
be viewed here:

http://git.kernel.org/?p=linux/kernel/git/dhowells/linux-modsign.git;a=shortlog;h=refs/heads/devel

The only significant difference between the version #3 patch posting I made
and the current code is that I've discarded the DSA algorithm and the
references to it.

I haven't included the MPI lib commits from Dmitry as they should be the same
as reside in your tree already.

David
---
The following changes since commit 7e8dec918ef8e0f68b4937c3c50fa57002077a4d:

  crypto: GnuPG based MPI lib - additional sources (part 4) (2011-11-09 11:47:26 +0200)

are available in the git repository at:
  git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-modsign.git devel

David Howells (20):
      MPILIB: Export some more symbols
      MPILIB: Add a missing ENOMEM check
      KEYS: Permit key_serial() to be called with a const key pointer
      KEYS: Move the key config into security/keys/Kconfig
      KEYS: Announce key type (un)registration
      KEYS: Reorganise keys Makefile
      KEYS: Create a key type that can be used for general cryptographic operations
      KEYS: Add signature verification facility
      KEYS: Asymmetric public-key algorithm crypto key subtype
      KEYS: RSA signature verification algorithm
      PGPLIB: PGP definitions (RFC 4880)
      PGPLIB: Basic packet parser
      PGPLIB: Signature parser
      KEYS: PGP data parser
      KEYS: PGP-based public key signature verification
      KEYS: PGP format signature parser
      KEYS: Provide a function to load keys from a PGP keyring blob
      MODSIGN: Add indications of module ELF types
      MODSIGN: Module ELF verifier
      MODSIGN: Apply signature checking to modules on module load

 .gitignore                             |   15 +
 Documentation/module-signing.txt       |  186 +++++++
 Documentation/security/keys-crypto.txt |  302 +++++++++++
 Makefile                               |    1 +
 arch/alpha/include/asm/module.h        |    3 +
 arch/arm/include/asm/module.h          |    5 +
 arch/cris/include/asm/module.h         |    5 +
 arch/h8300/include/asm/module.h        |    5 +
 arch/ia64/include/asm/module.h         |    5 +
 arch/m32r/include/asm/module.h         |    5 +
 arch/m68k/include/asm/module.h         |    5 +
 arch/mips/include/asm/module.h         |   12 +-
 arch/parisc/include/asm/module.h       |    8 +
 arch/powerpc/include/asm/module.h      |   10 +
 arch/s390/include/asm/module.h         |    3 +
 include/asm-generic/module.h           |   10 +
 include/keys/crypto-subtype.h          |   77 +++
 include/keys/crypto-type.h             |   37 ++
 include/linux/elfnote.h                |    4 +
 include/linux/key.h                    |    2 +-
 include/linux/modsign.h                |   27 +
 include/linux/module.h                 |    3 +
 include/linux/pgp.h                    |  255 +++++++++
 init/Kconfig                           |   65 +++
 kernel/Makefile                        |    4 +
 kernel/modsign-pubkey.c                |   44 ++
 kernel/module-verify-elf.c             |  344 ++++++++++++
 kernel/module-verify-sig.c             |  526 ++++++++++++++++++
 kernel/module-verify.c                 |   44 ++
 kernel/module-verify.h                 |   68 +++
 kernel/module.c                        |   25 +-
 lib/mpi/mpi-cmp.c                      |    2 +
 lib/mpi/mpi-div.c                      |    1 +
 lib/mpi/mpi-inv.c                      |    1 +
 lib/mpi/mpi-mpow.c                     |    1 +
 lib/mpi/mpi-mul.c                      |    1 +
 lib/mpi/mpicoder.c                     |    2 +
 net/dns_resolver/dns_key.c             |    5 -
 scripts/Makefile.modpost               |   85 +++-
 scripts/mod/.gitignore                 |    1 +
 scripts/mod/Makefile                   |    2 +-
 scripts/mod/mod-extract.c              |  913 ++++++++++++++++++++++++++++++++
 scripts/mod/modsign-note.sh            |   16 +
 security/Kconfig                       |   68 +---
 security/keys/Kconfig                  |  121 +++++
 security/keys/Makefile                 |   25 +-
 security/keys/crypto_keys.h            |   28 +
 security/keys/crypto_rsa.c             |  282 ++++++++++
 security/keys/crypto_type.c            |  228 ++++++++
 security/keys/crypto_verify.c          |  111 ++++
 security/keys/key.c                    |    3 +
 security/keys/pgp_key_parser.c         |  344 ++++++++++++
 security/keys/pgp_library.c            |  531 +++++++++++++++++++
 security/keys/pgp_parser.h             |   35 ++
 security/keys/pgp_preload.c            |   90 ++++
 security/keys/pgp_pubkey_sig.c         |  323 +++++++++++
 security/keys/pgp_sig_parser.c         |  104 ++++
 security/keys/public_key.c             |   55 ++
 security/keys/public_key.h             |  108 ++++
 59 files changed, 5506 insertions(+), 85 deletions(-)
 create mode 100644 Documentation/module-signing.txt
 create mode 100644 Documentation/security/keys-crypto.txt
 create mode 100644 include/keys/crypto-subtype.h
 create mode 100644 include/keys/crypto-type.h
 create mode 100644 include/linux/modsign.h
 create mode 100644 include/linux/pgp.h
 create mode 100644 kernel/modsign-pubkey.c
 create mode 100644 kernel/module-verify-elf.c
 create mode 100644 kernel/module-verify-sig.c
 create mode 100644 kernel/module-verify.c
 create mode 100644 kernel/module-verify.h
 create mode 100644 scripts/mod/mod-extract.c
 create mode 100644 scripts/mod/modsign-note.sh
 create mode 100644 security/keys/Kconfig
 create mode 100644 security/keys/crypto_keys.h
 create mode 100644 security/keys/crypto_rsa.c
 create mode 100644 security/keys/crypto_type.c
 create mode 100644 security/keys/crypto_verify.c
 create mode 100644 security/keys/pgp_key_parser.c
 create mode 100644 security/keys/pgp_library.c
 create mode 100644 security/keys/pgp_parser.h
 create mode 100644 security/keys/pgp_preload.c
 create mode 100644 security/keys/pgp_pubkey_sig.c
 create mode 100644 security/keys/pgp_sig_parser.c
 create mode 100644 security/keys/public_key.c
 create mode 100644 security/keys/public_key.h

Re: [GIT PULL] Crypto keys and module signing

[James Morris]

On Wed, 7 Dec 2011, David Howells wrote:

> 
> Hi James,
> 
> Could you pull my module signing code into the security tree?  The patches can
> be viewed here:

I'm getting this build error:

make[1]: *** No rule to make target `kernel.pub', needed by 
`kernel/modsign-pubkey.o'.  Stop.


> 
> http://git.kernel.org/?p=linux/kernel/git/dhowells/linux-modsign.git;a=shortlog;h=refs/heads/devel
> 
> The only significant difference between the version #3 patch posting I made
> and the current code is that I've discarded the DSA algorithm and the
> references to it.
> 
> I haven't included the MPI lib commits from Dmitry as they should be the same
> as reside in your tree already.
> 
> David
> ---
> The following changes since commit 7e8dec918ef8e0f68b4937c3c50fa57002077a4d:
> 
>   crypto: GnuPG based MPI lib - additional sources (part 4) (2011-11-09 11:47:26 +0200)
> 
> are available in the git repository at:
>   git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-modsign.git devel
> 
> David Howells (20):
>       MPILIB: Export some more symbols
>       MPILIB: Add a missing ENOMEM check
>       KEYS: Permit key_serial() to be called with a const key pointer
>       KEYS: Move the key config into security/keys/Kconfig
>       KEYS: Announce key type (un)registration
>       KEYS: Reorganise keys Makefile
>       KEYS: Create a key type that can be used for general cryptographic operations
>       KEYS: Add signature verification facility
>       KEYS: Asymmetric public-key algorithm crypto key subtype
>       KEYS: RSA signature verification algorithm
>       PGPLIB: PGP definitions (RFC 4880)
>       PGPLIB: Basic packet parser
>       PGPLIB: Signature parser
>       KEYS: PGP data parser
>       KEYS: PGP-based public key signature verification
>       KEYS: PGP format signature parser
>       KEYS: Provide a function to load keys from a PGP keyring blob
>       MODSIGN: Add indications of module ELF types
>       MODSIGN: Module ELF verifier
>       MODSIGN: Apply signature checking to modules on module load
> 
>  .gitignore                             |   15 +
>  Documentation/module-signing.txt       |  186 +++++++
>  Documentation/security/keys-crypto.txt |  302 +++++++++++
>  Makefile                               |    1 +
>  arch/alpha/include/asm/module.h        |    3 +
>  arch/arm/include/asm/module.h          |    5 +
>  arch/cris/include/asm/module.h         |    5 +
>  arch/h8300/include/asm/module.h        |    5 +
>  arch/ia64/include/asm/module.h         |    5 +
>  arch/m32r/include/asm/module.h         |    5 +
>  arch/m68k/include/asm/module.h         |    5 +
>  arch/mips/include/asm/module.h         |   12 +-
>  arch/parisc/include/asm/module.h       |    8 +
>  arch/powerpc/include/asm/module.h      |   10 +
>  arch/s390/include/asm/module.h         |    3 +
>  include/asm-generic/module.h           |   10 +
>  include/keys/crypto-subtype.h          |   77 +++
>  include/keys/crypto-type.h             |   37 ++
>  include/linux/elfnote.h                |    4 +
>  include/linux/key.h                    |    2 +-
>  include/linux/modsign.h                |   27 +
>  include/linux/module.h                 |    3 +
>  include/linux/pgp.h                    |  255 +++++++++
>  init/Kconfig                           |   65 +++
>  kernel/Makefile                        |    4 +
>  kernel/modsign-pubkey.c                |   44 ++
>  kernel/module-verify-elf.c             |  344 ++++++++++++
>  kernel/module-verify-sig.c             |  526 ++++++++++++++++++
>  kernel/module-verify.c                 |   44 ++
>  kernel/module-verify.h                 |   68 +++
>  kernel/module.c                        |   25 +-
>  lib/mpi/mpi-cmp.c                      |    2 +
>  lib/mpi/mpi-div.c                      |    1 +
>  lib/mpi/mpi-inv.c                      |    1 +
>  lib/mpi/mpi-mpow.c                     |    1 +
>  lib/mpi/mpi-mul.c                      |    1 +
>  lib/mpi/mpicoder.c                     |    2 +
>  net/dns_resolver/dns_key.c             |    5 -
>  scripts/Makefile.modpost               |   85 +++-
>  scripts/mod/.gitignore                 |    1 +
>  scripts/mod/Makefile                   |    2 +-
>  scripts/mod/mod-extract.c              |  913 ++++++++++++++++++++++++++++++++
>  scripts/mod/modsign-note.sh            |   16 +
>  security/Kconfig                       |   68 +---
>  security/keys/Kconfig                  |  121 +++++
>  security/keys/Makefile                 |   25 +-
>  security/keys/crypto_keys.h            |   28 +
>  security/keys/crypto_rsa.c             |  282 ++++++++++
>  security/keys/crypto_type.c            |  228 ++++++++
>  security/keys/crypto_verify.c          |  111 ++++
>  security/keys/key.c                    |    3 +
>  security/keys/pgp_key_parser.c         |  344 ++++++++++++
>  security/keys/pgp_library.c            |  531 +++++++++++++++++++
>  security/keys/pgp_parser.h             |   35 ++
>  security/keys/pgp_preload.c            |   90 ++++
>  security/keys/pgp_pubkey_sig.c         |  323 +++++++++++
>  security/keys/pgp_sig_parser.c         |  104 ++++
>  security/keys/public_key.c             |   55 ++
>  security/keys/public_key.h             |  108 ++++
>  59 files changed, 5506 insertions(+), 85 deletions(-)
>  create mode 100644 Documentation/module-signing.txt
>  create mode 100644 Documentation/security/keys-crypto.txt
>  create mode 100644 include/keys/crypto-subtype.h
>  create mode 100644 include/keys/crypto-type.h
>  create mode 100644 include/linux/modsign.h
>  create mode 100644 include/linux/pgp.h
>  create mode 100644 kernel/modsign-pubkey.c
>  create mode 100644 kernel/module-verify-elf.c
>  create mode 100644 kernel/module-verify-sig.c
>  create mode 100644 kernel/module-verify.c
>  create mode 100644 kernel/module-verify.h
>  create mode 100644 scripts/mod/mod-extract.c
>  create mode 100644 scripts/mod/modsign-note.sh
>  create mode 100644 security/keys/Kconfig
>  create mode 100644 security/keys/crypto_keys.h
>  create mode 100644 security/keys/crypto_rsa.c
>  create mode 100644 security/keys/crypto_type.c
>  create mode 100644 security/keys/crypto_verify.c
>  create mode 100644 security/keys/pgp_key_parser.c
>  create mode 100644 security/keys/pgp_library.c
>  create mode 100644 security/keys/pgp_parser.h
>  create mode 100644 security/keys/pgp_preload.c
>  create mode 100644 security/keys/pgp_pubkey_sig.c
>  create mode 100644 security/keys/pgp_sig_parser.c
>  create mode 100644 security/keys/public_key.c
>  create mode 100644 security/keys/public_key.h
> 

-- 
James Morris
<jmorris@namei.org>

Re: [GIT PULL] Crypto keys and module signing

[David Howells]

James Morris <jmorris@namei.org> wrote:

> > Could you pull my module signing code into the security tree?  The patches can
> > be viewed here:
> 
> I'm getting this build error:
> 
> make[1]: *** No rule to make target `kernel.pub', needed by 
> `kernel/modsign-pubkey.o'.  Stop.

If you turn module signing on, you have to supply keys for it to sign things
with and to later verify the signature...

I wonder what the best way to deal with that is...  I guess make allyesconfig
and make allmodconfig are going to break otherwise.

David

Re: [GIT PULL] Crypto keys and module signing

[James Morris]

On Fri, 9 Dec 2011, David Howells wrote:

> James Morris <jmorris@namei.org> wrote:
> 
> > > Could you pull my module signing code into the security tree?  The patches can
> > > be viewed here:
> > 
> > I'm getting this build error:
> > 
> > make[1]: *** No rule to make target `kernel.pub', needed by 
> > `kernel/modsign-pubkey.o'.  Stop.
> 
> If you turn module signing on, you have to supply keys for it to sign things
> with and to later verify the signature...
> 
> I wonder what the best way to deal with that is...  I guess make allyesconfig
> and make allmodconfig are going to break otherwise.

Create a dummy key?


-- 
James Morris
<jmorris@namei.org>

Re: [GIT PULL] Crypto keys and module signing

[Arjan van de Ven]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 12/9/2011 1:17 AM, David Howells wrote:
> James Morris <jmorris@namei.org> wrote:
> 
>>> Could you pull my module signing code into the security tree?
>>> The patches can be viewed here:
>> 
>> I'm getting this build error:
>> 
>> make[1]: *** No rule to make target `kernel.pub', needed by 
>> `kernel/modsign-pubkey.o'.  Stop.
> 
> If you turn module signing on, you have to supply keys for it to
> sign things with and to later verify the signature...
> 
> I wonder what the best way to deal with that is...  I guess make
> allyesconfig and make allmodconfig are going to break otherwise.

the best way to deal is to have KBUILD generate a key on demand ;-)

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.17 (MingW32)

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=gfR7
-----END PGP SIGNATURE-----

Re: [GIT PULL] Crypto keys and module signing

[James Morris]

On Fri, 9 Dec 2011, Arjan van de Ven wrote:

> the best way to deal is to have KBUILD generate a key on demand ;-)

Yes -- I'd like to see this code do something useful by default when 
enabled, so yes, create a local key during the build, possibly 
configurable via kconfig.

Is there any reason not to sign and verify kernel modules by default?



- James
-- 
James Morris
<jmorris@namei.org>

Re: [GIT PULL] Crypto keys and module signing

[David Howells]

James Morris <jmorris@namei.org> wrote:

> Is there any reason not to sign and verify kernel modules by default?

If you don't have an entropy source, your build can hang if it's waiting for
gpg to generate a key.  You need to run rngd to get around this.

David

Re: [GIT PULL] Crypto keys and module signing

[Arjan van de Ven]

On 12/9/2011 10:06 AM, David Howells wrote:
> James Morris <jmorris@namei.org> wrote:
> 
>> Is there any reason not to sign and verify kernel modules by default?
> 
> If you don't have an entropy source, your build can hang if it's waiting for
> gpg to generate a key.  You need to run rngd to get around this.

... the temp key can use /dev/urandom.
seriously, /dev/urandom for one time, temp keys is not bad
(if you care about the difference, you better provide your own real key)

Re: [GIT PULL] Crypto keys and module signing

[David Howells]

Arjan van de Ven <arjan@linux.intel.com> wrote:

> ... the temp key can use /dev/urandom.
> seriously, /dev/urandom for one time, temp keys is not bad
> (if you care about the difference, you better provide your own real key)

Can you tell gpg which random device to use?

David

Re: [GIT PULL] Crypto keys and module signing

[Arjan van de Ven]

On 12/9/2011 10:47 AM, David Howells wrote:
> Arjan van de Ven <arjan@linux.intel.com> wrote:
> 
>> ... the temp key can use /dev/urandom.
>> seriously, /dev/urandom for one time, temp keys is not bad
>> (if you care about the difference, you better provide your own real key)
> 
> Can you tell gpg which random device to use?
> 
> David

see
http://www.gnupg.org/documentation/manuals/gnupg-devel/Unattended-GPG-key-generation.html

Re: [GIT PULL] Crypto keys and module signing

[David Howells]

Arjan van de Ven <arjan@linux.intel.com> wrote:

> see
> http://www.gnupg.org/documentation/manuals/gnupg-devel/Unattended-GPG-key-generation.html

"%transient-key"?

David

Re: [Keyrings] [GIT PULL] Crypto keys and module signing

[Daniel Kahn Gillmor]

[-- Attachment #1: Type: text/plain, Size: 528 bytes --]

On 12/09/2011 01:47 PM, David Howells wrote:
> Arjan van de Ven <arjan@linux.intel.com> wrote:
> 
>> ... the temp key can use /dev/urandom.
>> seriously, /dev/urandom for one time, temp keys is not bad
>> (if you care about the difference, you better provide your own real key)
> 
> Can you tell gpg which random device to use?

Depending on the version of gpg, supplying either --quick-random or
--debug-quick-random should use a cheaper PRNG.

I think this is an undocumented feature, though.

hth,

	--dkg


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 1030 bytes --]

Re: [GIT PULL] Crypto keys and module signing

[Geert Uytterhoeven]

On Fri, Dec 9, 2011 at 15:20, Arjan van de Ven <arjan@linux.intel.com> wrote:
>> I wonder what the best way to deal with that is...  I guess make
>> allyesconfig and make allmodconfig are going to break otherwise.
>
> the best way to deal is to have KBUILD generate a key on demand ;-)

Or provide a default key with the kernel, cfr. all the other "*.shipped" files?
No entropy source needed.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [GIT PULL] Crypto keys and module signing

[Arkadiusz Miśkiewicz]

On Wed, Dec 7, 2011 at 3:47 PM, David Howells <dhowells@redhat.com> wrote:
>
> Hi James,
>
> Could you pull my module signing code into the security tree?  The patches can
> be viewed here:
>
> http://git.kernel.org/?p=linux/kernel/git/dhowells/linux-modsign.git;a=shortlog;h=refs/heads/devel

If I understand it is not possible to sign modules after they are
built and load keys without actually
rebuilding kernel?

For distro kernel the public and secret keys have to be available
publicly, right? Otherwise people
using distro kernels won't be able to build own signed modules for use
with that distro kernel.

Then I as admin have to rebuild the kernel to get my own keys in and
prevent other, "unapproved" modules
to be loaded. Correct?

Would be nice if the modules could be signed/re-signed after being
build and prehaps kernel could
load keys from initramfs? Then everyone could use own keys on distro
kernels without need to rebuild
the thing.

I think I'm missing something :)

-- 
Arkadiusz Miśkiewicz

Re: [GIT PULL] Crypto keys and module signing

[David Howells]

Arkadiusz Miśkiewicz <a.miskiewicz@gmail.com> wrote:

> If I understand it is not possible to sign modules after they are built

Well, modules are signed after they're built.  It's a matter of creating a
detached signature for the parts of the module file you want to protect and
then inserting the signature into the module file.  I've created a way to do
this as part of the build process, but previously we had the spec file do it
during the kernel RPM build.

> and load keys without actually rebuilding kernel?

Well, yes and no.

The way we have used up to now involves building a set of public keys into the
kernel so that modules can be verified with them during loading.  We could make
a way to load extra keys, but how does the kernel know it can trust those keys?

With the new mechanism in the patches I've submitted, there is the possibility
of using a cryptographic key storage hardware (such as a TPM) to directly store
either extra public keys that you want to be able to verify modules with, or to
hold a key you sign the extra public keys with.

That way you can have modules signed with the kernel's build-time temporary key
and also have modules signed with other keys that are trusted by the
administrator.

> For distro kernel the public and secret keys have to be available publicly,
> right?

No.  The public key has to be publically available, but the secret key must be
kept, well, secret - otherwise there's no point.  If anyone can sign a module
to run on your system, then the signature mechanism may as well not be there.

RHEL keeps the secret key as secret as it possibly can by generating a new one
each time a kernel RPM is built and then it's deleted afterwards when the BUILD
directory is cleaned up.  No record of the secret key is kept.  It's not easy
to have the buildfarm save the secret key in a database somewhere as anyone who
gets hold of a RHEL kernel SRPM and wants to build it mustn't find the build
fails because the secret-key-save mechanism doesn't work.  Besides - you don't
want it quietly saving your privately built secret key to Red Hat's big
database, right?

> Otherwise people using distro kernels won't be able to build own signed
> modules for use with that distro kernel.

That's the whole point...  To a point.  You can still load unsigned modules,
but it makes a fuss in the syslog, and you can block unsigned modules.
Hopefully at some time in the future, as mentioned above, you'll be able to use
hardware for this.

> Then I as admin have to rebuild the kernel to get my own keys in and prevent
> other, "unapproved" modules to be loaded. Correct?

Correct.  You could, theoretically, extract the public keys from the kernel
you're rebuilding and include those too, but it's messy.

> Would be nice if the modules could be signed/re-signed after being build

That's relatively straight forward.  You can strip the existing signatures and
replace them with your own.  The modules are really signed *after* being built
- after all, you don't know what it is you're going to be signing until after
the things are built.

> and prehaps kernel could load keys from initramfs?

How do you trust the keys?  If you have a TPM, then yes you can do that.

In fact, how do you trust the public key compiled into the kernel for that
matter?  Ideally, the bootloader would have to check that the kernel image
hasn't been tampered with.  That's easier than checking the initramfs as the
kernel is not changed after building, whereas the initramfs is.

> Then everyone could use own keys on distro kernels without need to rebuild
> the thing.
> 
> I think I'm missing something :)

Perhaps I can summarise:

 (1) The whole point of having a secret key is that you tell as few people as
     absolutely possible what it is.

 (2) Public keys have to be trusted in order for you to use them.

 (3) Cryptography is, by its very nature, inconvenient.  But it only works if
     you inconvenience people who shouldn't have access more than you
     inconvenience those who should.

David

Re: [GIT PULL] Crypto keys and module signing

[Arjan van de Ven]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 12/10/2011 3:42 AM, Arkadiusz Miśkiewicz wrote:
> On Wed, Dec 7, 2011 at 3:47 PM, David Howells <dhowells@redhat.com>
> wrote:
>> 
>> Hi James,
>> 
>> Could you pull my module signing code into the security tree?
>> The patches can be viewed here:
>> 
>> http://git.kernel.org/?p=linux/kernel/git/dhowells/linux-modsign.git;a=shortlog;h=refs/heads/devel
>
>> 
> If I understand it is not possible to sign modules after they are 
> built and load keys without actually rebuilding kernel?

only if the end user chooses to enforce the signature.

> 
> For distro kernel the public and secret keys have to be available 
> publicly, right? Otherwise people using distro kernels won't be
> able to build own signed modules for use with that distro kernel.

That's a distro choice, but... again:

only if the user chooses to enforce the signature.
Very few people actually build their own modules, and for the people
that don't, they can chose to harden their server by only allowing
signed (eg distro shipped) modules.

For those who prefer to build a few other things and still want
security, they can also rebuild the kernel.

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Re: [GIT PULL] Crypto keys and module signing

[Nick Bowler]

On 2011-12-10 12:50 +0000, David Howells wrote:
> Arkadiusz Miśkiewicz <a.miskiewicz@gmail.com> wrote:
> > and prehaps kernel could load keys from initramfs?
> 
> How do you trust the keys?  If you have a TPM, then yes you can do that.

Exactly the same way you trust the kernel image itself.  If you can't
trust the integrity of your initramfs (and thus the keys stored within
it), then you also cannot trust the integrity of the kernel image and
thus this whole signing exercise is moot.

Cheers,
-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)