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

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

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.

Cheers,
Ahmad

> 
> Tim
> 


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