Re: [PATCH 0/4] KEYS: trusted: Introduce support for NXP CAAM-based trusted keys

[Tim Harvey <tharvey@gateworks.com>]

On Fri, Aug 20, 2021 at 1:36 PM Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>
> On 20.08.21 22:20, Tim Harvey wrote:
> > On Fri, Aug 20, 2021 at 9:20 AM Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
> >> On 20.08.21 17:39, Tim Harvey wrote:
> >>> Thanks for your work!
> >>>
> >>> I've been asked to integrate the capability of using CAAM to
> >>> blob/deblob data to an older 5.4 kernel such as NXP's downstream
> >>> vendor kernel does [1] and I'm trying to understand how your series
> >>> works. I'm not at all familiar with the Linux Key Management API's or
> >>> trusted keys. Can you provide an example of how this can be used for
> >>> such a thing?
> >>
> >> Here's an example with dm-crypt:
> >>
> >>   https://lore.kernel.org/linux-integrity/5d44e50e-4309-830b-79f6-f5d888b1ef69@pengutronix.de/
> >>
> >> dm-crypt is a bit special at the moment, because it has direct support for
> >> trusted keys. For interfacing with other parts of the kernel like ecryptfs
> >> or EVM, you have to create encrypted keys rooted to the trusted keys and use
> >> those. The kernel documentation has an example:
> >>
> >>   https://www.kernel.org/doc/html/v5.13/security/keys/trusted-encrypted.html
> >>
> >> If you backport this series, you can include the typo fix spotted by David.
> >>
> >> I'll send out a revised series, but given that a regression fix I want to
> >> rebase on hasn't been picked up for 3 weeks now, I am not in a hurry.
> >>
> > Thanks for the reference.
> >
> > I'm still trying to understand the keyctl integration with caam. For
> > the 'data' param to keyctl you are using tings like 'new <len>' and
> > 'load <data>'. Where are these 'commands' identified?
>
> Search for match_table_t in security/keys/trusted-keys/trusted_core.c
>
> > I may still be missing something. I'm using 4.14-rc6 with your series
> > and seeing the following:
>
> That's an odd version to backport stuff to..
>
> > # cat /proc/cmdline
> > trusted.source=caam
> > # keyctl add trusted mykey 'new 32' @s)# create new trusted key named
> > 'mykey' of 32 bytes in the session keyring
> > 480104283
> > # keyctl print 480104283 # dump the key
> > keyctl_read_alloc: Unknown error 126
> > ^^^ not clear what this is
>
> Not sure what returns -ENOKEY for you. I haven't been using trusted
> keys on v4.14, but you can try tracing the keyctl syscall.

yikes... that would be painful. I typo'd and meant 5.14-rc6 :) I'm
working with mainline first to make sure I understand everything. If I
backport this it would be to 5.4 but that looks to be extremely
painful. It looks like there was a lot of activity around trusted keys
in 5.13.

It works for a user keyring but not a session keyring... does that
explain anything?
# keyctl add trusted mykey 'new 32' @u
941210782
# keyctl print 941210782
83b7845cb45216496aead9ee2c6a406f587d64aad47bddc539d8947a247e618798d9306b36398b5dc2722a4c3f220a3a763ee175f6bd64758fdd49ca4db597e8ce328121b60edbba9b8d8d55056be896
# keyctl add trusted mykey 'new 32' @s
310571960
# keyctl print 310571960
keyctl_read_alloc: Unknown error 126

Sorry, I'm still trying to wrap my head around the differences in
keyrings and trusted vs user keys.

Tim