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: <20170201144837.aenzg5cauzl2ofbt@intel.com>
Date:   Wed, 1 Feb 2017 16:48:59 +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 Tue, Jan 31, 2017 at 10:50:06PM +0200, 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.
> 
> > 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.

rc = tpm_transmit_cmd(chip, buf.data, tpm_buf_length(&buf), 0, 0,
		      "attempting extend a PCR value");

This should be

rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, 0, 0,
		      "attempting extend a PCR value");

The second parameter is the size of the buffer, not length of the input
data.

I'll update this...

/Jarkko