linux-kernel - Re: Fwd: Re: [tpmdd-devel] [PATCH v9 2/2] tpm: add securityfs support,for TPM 2.0 firmware event log

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Message-Id: <58918EBA.1000103@linux.vnet.ibm.com>
Date:   Wed, 1 Feb 2017 13:01:06 +0530
From:   Nayna <nayna@...ux.vnet.ibm.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Kenneth Goldman <kgoldman@...ibm.com>,
        "moderated list:TPM DEVICE DRIVER" 
        <tpmdd-devel@...ts.sourceforge.net>,
        open list <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org
Subject: Re: Fwd: Re: [tpmdd-devel] [PATCH v9 2/2] tpm: add securityfs
 support,for TPM 2.0 firmware event log



On 02/01/2017 02:20 AM, Jarkko Sakkinen wrote:
> On Wed, Feb 01, 2017 at 12:14:12AM +0530, Nayna wrote:
>>> I already sent my pull request to 4.11 and even today I found something
>>> fishy. You declared a function local array by using a variable in "tpm:
>>> enhance TPM 2.0 PCR extend to support multiple banks" (max_active_banks
>>> or something). And the event log patches have just passed the review.
>>
>> Yes. I have checked using clang and it has passed the clang.. and I also
>> verified there were no complains during build.
>
> What we can deduce from that is that they didn't expose the issue in
> question.
>
> I found this by running sparse with make C=2 M=drives/char/tpm
>
>> What type of problem do you see ?
>
> It is disallowed to do stack allocation in the kernel code even if C
> standard would allow it. Stack is scarce resource so you need to know
> its usage at compile time.
>
> In this case you actually know the allocation because the value is not
> changed during the course of the function but it is still bad. Probably
> compiler will optimize it out. Still it is not a good practice.

Thanks Jarkko for explaining it.

Hmm, do you want me to send a patch for this ?
I think what we want is actually define it just array of size as 7.

>
>> Also, to understand, this is related to multi-bank patchset. I mean how does
>> it affect for event log patchset ?
>
> Well in both cases these have landed fairly late but I asked from James
> whether I'll have to postpone these to 4.12.
>
> Usually when I've sent my release pull request I do not want to make any
> radical changes to the codebase because they always require extra QA and
> thus take extra time.

Thanks again for explaining details.

Thanks & Regards,
    - Nayna

>
> /Jarkko
>