[PATCH] ima: debugging late_initcall_sync measurements

[Paul Moore]

On May 5, 2026 9:57:23 PM Mimi Zohar <zohar at linux.ibm.com> wrote:
> On Tue, 2026-05-05 at 18:55 -0400, Paul Moore wrote:
>> On Tue, May 5, 2026 at 5:05 PM Mimi Zohar <zohar at linux.ibm.com> wrote:
>>> On Mon, 2026-05-04 at 16:51 -0400, Paul Moore wrote:
>>>> On Mon, May 4, 2026 at 8:03 AM Mimi Zohar <zohar at linux.ibm.com> wrote:
>>>>> On Sun, 2026-05-03 at 12:46 -0400, Paul Moore wrote:
>>>>>> Regardless, assuming you always want IMA to leverage a TPMs when they
>>>>>> exist, your reply suggests that using an initcall based IMA init
>>>>>> scheme, even a late-sync initcall, may not be sufficient because
>>>>>> deferred TPM initialization could happen later, yes?
>>>>>
>>>>> Well yeah.  The TPM could be configured as a module, but that scenario is 
>>>>> not of
>>>>> interest.  That's way too late.  The case being addressed in this patch set is
>>>>> when the TPM driver tries to initialize at device_initcall, returns
>>>>> EPROBE_DEFER, and is retried at deferred_probe_initcall (late_initcall).  Since
>>>>> ordering within an initcall is not supported, this patch attempts to initialize
>>>>> IMA at late_initcall and similarly retries, in this case, at 
>>>>> late_initcall_sync.
>>>>
>>>> Okay, so from a TPM initialization perspective you are satisfied with
>>>> a late-sync IMA initialization, yes?
>>>
>>> No. On some architectures moving IMA initialization from the late_initcall to
>>> late_initcall_sync does not miss any measurement records. However, as 
>>> previously
>>> mentioned, Linux running in a PowerVM LPAR the move would drop ~30 measurement
>>> records[1].  So no, only if the TPM is not initialized by late_initcall, should
>>> IMA retry at late_initcall_sync.
>>
>> What do you do in the PowerVM LPAR when the TPM is not avaiable at
>> late initcall and you have to defer IMA initialization until
>> late-sync?
>
> Your question is hypothetical ...

<heavy eye roll>

> ... as the TPM isn't deferred, so IMA doesn't go into
> TPM-bypass mode.  Testing on a PowerVM LPAR demonstrated that it skips ~30
> measurement list records.  So moving the initcall to late_initcall_sync would
> cause a regression.

Let me rephrase to make the question clear - how do you plan to handle a 
system where you lose measurements by waiting until late-sync, but the TPM 
is not available at the late initcall.

--
paul-moore.com