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

[Tim Harvey <tharvey@gateworks.com>]

On Mon, Aug 23, 2021 at 6:29 AM Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>
> Hello Tim,
>
> On 20.08.21 23:19, Tim Harvey wrote:
> > 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.
>
> Ye. It used to be limited to TPM before that.
>
> > 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
>
> Both sequences work for me.
>
> My getty is started by systemd. I think systemd allocates a new session
> keyring for the getty that's inherited by the shell and the commands I run
> it in. If you don't do that, each command will get its own session key.
>
> > Sorry, I'm still trying to wrap my head around the differences in
> > keyrings and trusted vs user keys.
>
> No problem. HTH.

Ahmad,

Ok that explains it - my testing is using a very basic buildroot
ramdisk rootfs. If I do a 'keyctl new_session' first I can use the
system keyring fine as well.

Thanks - hoping to see this merged soon!

Tim