mbox series

[0/2] Add support for ECDSA-signed kernel modules

Message ID 20210406185340.1079403-1-stefanb@linux.ibm.com (mailing list archive)
Headers show
Series Add support for ECDSA-signed kernel modules | expand

Message

Stefan Berger April 6, 2021, 6:53 p.m. UTC
This series adds support for ECDSA-signed kernel modules.

The first patch in this series attempts to address the issue where a
developer created an ECDSA key for signing modules and then falls back
to compiling an older version of the kernel that does not support
ECDSA keys. In this case this patch would delete that ECDSA key if it is
in certs/signing_key.pem and trigger the creation of an RSA key. However,
for this to work this patch would have to be applied to previous versions
of the kernel but would also only work for the developer if he/she used a
stable version of the kernel to which this patch was applied. So whether
this patch actually achieves the wanted effect is not always guaranteed.

The 2nd patch adds the support for the ECSDA-signed kernel modules.

This series depends on Nayna's series https://lkml.org/lkml/2021/3/30/571
and my ECDSA support series currently queued here:
https://git.kernel.org/pub/scm/linux/kernel/git/herbert/cryptodev-2.6.git/log/?h=ecc

  Stefan

Stefan Berger (2):
  certs: Trigger recreation of module signing key if it's not an RSA key
  certs: Add support for using elliptic curve keys for signing modules

 certs/Kconfig                         | 25 +++++++++++++++++++++++++
 certs/Makefile                        | 14 ++++++++++++++
 crypto/asymmetric_keys/pkcs7_parser.c |  4 ++++
 3 files changed, 43 insertions(+)

Comments

jarkko@kernel.org April 7, 2021, 3:53 p.m. UTC | #1
On Tue, Apr 06, 2021 at 02:53:38PM -0400, Stefan Berger wrote:
> This series adds support for ECDSA-signed kernel modules.
> 
> The first patch in this series attempts to address the issue where a
> developer created an ECDSA key for signing modules and then falls back
> to compiling an older version of the kernel that does not support
> ECDSA keys. In this case this patch would delete that ECDSA key if it is
> in certs/signing_key.pem and trigger the creation of an RSA key. However,
> for this to work this patch would have to be applied to previous versions
> of the kernel but would also only work for the developer if he/she used a
> stable version of the kernel to which this patch was applied. So whether
> this patch actually achieves the wanted effect is not always guaranteed.

Just wondering why the key needs to be removed in the fallback.

/Jarkko
Mimi Zohar April 7, 2021, 4:10 p.m. UTC | #2
On Wed, 2021-04-07 at 18:53 +0300, Jarkko Sakkinen wrote:
> On Tue, Apr 06, 2021 at 02:53:38PM -0400, Stefan Berger wrote:
> > This series adds support for ECDSA-signed kernel modules.
> > 
> > The first patch in this series attempts to address the issue where a
> > developer created an ECDSA key for signing modules and then falls back
> > to compiling an older version of the kernel that does not support
> > ECDSA keys. In this case this patch would delete that ECDSA key if it is
> > in certs/signing_key.pem and trigger the creation of an RSA key. However,
> > for this to work this patch would have to be applied to previous versions
> > of the kernel but would also only work for the developer if he/she used a
> > stable version of the kernel to which this patch was applied. So whether
> > this patch actually achieves the wanted effect is not always guaranteed.
> 
> Just wondering why the key needs to be removed in the fallback.

The main concern is with bisecting the kernel.  Either elliptic curve
support or the first patch needs to be backported.  This patch will
cause the kernel module signing key to be regenerated.

Mimi
Stefan Berger April 7, 2021, 5:53 p.m. UTC | #3
On 4/7/21 12:10 PM, Mimi Zohar wrote:
> On Wed, 2021-04-07 at 18:53 +0300, Jarkko Sakkinen wrote:
>> On Tue, Apr 06, 2021 at 02:53:38PM -0400, Stefan Berger wrote:
>>> This series adds support for ECDSA-signed kernel modules.
>>>
>>> The first patch in this series attempts to address the issue where a
>>> developer created an ECDSA key for signing modules and then falls back
>>> to compiling an older version of the kernel that does not support
>>> ECDSA keys. In this case this patch would delete that ECDSA key if it is
>>> in certs/signing_key.pem and trigger the creation of an RSA key. However,
>>> for this to work this patch would have to be applied to previous versions
>>> of the kernel but would also only work for the developer if he/she used a
>>> stable version of the kernel to which this patch was applied. So whether
>>> this patch actually achieves the wanted effect is not always guaranteed.
>> Just wondering why the key needs to be removed in the fallback.
Because if you signed an older kernel's modules with the ECDSA key it 
won't be able to load the modules...
> The main concern is with bisecting the kernel.  Either elliptic curve
> support or the first patch needs to be backported.  This patch will
> cause the kernel module signing key to be regenerated.


This assumes of course that one will bisect via the stable kernels where 
this 1st patch has been applied. Not sure whether that's what people 
will do.

    Stefan


>
> Mimi
>
jarkko@kernel.org April 7, 2021, 8:15 p.m. UTC | #4
On Wed, Apr 07, 2021 at 01:53:24PM -0400, Stefan Berger wrote:
> 
> On 4/7/21 12:10 PM, Mimi Zohar wrote:
> > On Wed, 2021-04-07 at 18:53 +0300, Jarkko Sakkinen wrote:
> > > On Tue, Apr 06, 2021 at 02:53:38PM -0400, Stefan Berger wrote:
> > > > This series adds support for ECDSA-signed kernel modules.
> > > > 
> > > > The first patch in this series attempts to address the issue where a
> > > > developer created an ECDSA key for signing modules and then falls back
> > > > to compiling an older version of the kernel that does not support
> > > > ECDSA keys. In this case this patch would delete that ECDSA key if it is
> > > > in certs/signing_key.pem and trigger the creation of an RSA key. However,
> > > > for this to work this patch would have to be applied to previous versions
> > > > of the kernel but would also only work for the developer if he/she used a
> > > > stable version of the kernel to which this patch was applied. So whether
> > > > this patch actually achieves the wanted effect is not always guaranteed.
> > > Just wondering why the key needs to be removed in the fallback.
> Because if you signed an older kernel's modules with the ECDSA key it won't
> be able to load the modules...
> > The main concern is with bisecting the kernel.  Either elliptic curve
> > support or the first patch needs to be backported.  This patch will
> > cause the kernel module signing key to be regenerated.
> 
> 
> This assumes of course that one will bisect via the stable kernels where
> this 1st patch has been applied. Not sure whether that's what people will
> do.

In any case, sounds non-trivial issue enough ought to be documented in the
commit message.

/Jarkko