[RFC] integrity: wait for completion of i2c initialization using late_initcall_sync()

[Romain Naour]

Hi Mimi,

Le 11/07/2024 à 16:06, Mimi Zohar a écrit :
> On Mon, 2024-07-01 at 22:37 -0400, Mimi Zohar wrote:
>> Hi Romain,
>>
>> Please limit the subject line to 70 - 75 characters.
>>
>>
>> On Mon, 2024-07-01 at 16:58 +0200, Romain Naour wrote:
>>>>> [1]
>>>>> https://lore.kernel.org/linux-integrity/9b98d912-ba78-402c-a5c8-154bef8794f7@smile.fr/
>>>>> [2]
>>>>> https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1375425/tda4vm-ima-vs-tpm-builtin-driver-boot-order
>>>>>
>>>>> Signed-off-by: Romain Naour <romain.naour at skf.com>
>>>>
>>>> Should this get a Fixes: tag and be also applied to the stable series?
>>>
>>> The current behavior can be reproduced on any released kernel (at least since
>>> 6.1). But I'm not sure if it should be backported to stable kernels since it
>>> delays the ima/evm initialization at runtime.
>>
>> With the IMA builtin measurement policy specified on the boot command line
>> ("ima_policy=tcb"), moving init_ima from the late_initcall() to
>> late_initcall_sync() affects the measurement list order.  It's unlikely, but
>> possible, that someone is sealing the TPM to PCR-10.  It's probably not a good
>> idea to backport the change.
>>
>> An alternative would be to continue using the late_initcall(), but retry on
>> failure, instead of going directly into TPM-bypass mode.

Indeed, it would be better if the IMA (and EVM) can use something like EPROBE_DEFER.

>>
>> As far as I can tell, everything is still being measured and verified, but more
>> testing is required.

Agree, I'm still evaluating the TPM stack when time allows.

> 
> Romain, Paul, another report of IMA going into TPM-bypass mode is here: 
> https://github.com/raspberrypi/linux/issues/6217.  Deferring IMA initialization
> to late_initcall_sync() did not resolve the problem for them.  Please take a
> look at the report.

I don't think that the "mdelay(200)" is really needed when late_initcall_sync()
is used. I guess the issue was the spi driver was not builtin, fixed by:

CONFIG_SPI_DESIGNWARE=y
CONFIG_SPI_DW_MMIO=y

Best regards,
Romain


> 
> thanks,
> 
> Mimi
>