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: <20170201182757.j32w4zbwr5syx7kv@intel.com>
Date:   Wed, 1 Feb 2017 20:27:57 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Nayna <nayna@...ux.vnet.ibm.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 Wed, Feb 01, 2017 at 01:01:06PM +0530, Nayna wrote:
> 
> 
> 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.

No but please test my tree and check that it still works.

/Jarkko