Subject: Re: [PATCH] ima: remove ACPI dependency
From: Eric Paris <eparis@redhat.com>
To: David Safford <safford@watson.ibm.com>
Cc: Eric Paris <eparis@parisplace.org>, Mimi Zohar <zohar@linux.vnet.ibm.com>,
       linux-kernel@vger.kernel.org, James Morris <jmorris@namei.org>,
       Rajiv Andrade <srajiv@linux.vnet.ibm.com>,
       Jean-Christophe Dubois <jcd@tribudubois.net>,
       Mimi Zohar <zohar@us.ibm.com>, Stable Kernel <stable@kernel.org>
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Date: Tue, 27 Oct 2009 16:56:50 -0400
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On Tue, 2009-10-27 at 16:42 -0400, David Safford wrote:
> On Tue, 2009-10-27 at 12:36 -0400, Eric Paris wrote:
> > On Tue, 2009-10-27 at 11:59 -0400, David Safford wrote:
> > > Basically, if running on a system with a TPM, IMA wants the TPM
> > > boot measurement log, which the TPM driver can only get through
> > > ACPI. If the platform does not have a TPM, then IMA does not 
> > > need ACPI.
> > 
> > I'm afraid I'm not seeing the connection.  Where does IMA gets the boot
> > measurement log?  I see that the TPM exports that log in securityfs as 2
> > files (ascii and binary) in tpm_bios.c but I don't see how IMA ever
> > makes use of that log either internally to the kernel or through the
> > securityfs files.
> > 
> sorry - bad explanation. IMA reads PCR 0-7, and combines them into
> a single "boot_aggregate" as the first entry in the IMA list. For full
> attestation, a user level program needs access to both IMA's
> boot aggregate, and to the detailed TPM event log upon which
> the aggregate is based. So IMA does not itself access the logs,
> but the boot aggregate is less useful without them.

So users of IMA in userspace may want TPM.  Shouldn't the kernel really
have this as a depends/select in the TPM code?  This isn't IMA specific,
it's TPM specific.  Obviously I'm not a fan of the spurious ACPI
requirement in the IMA code.  How about a 'CONFIG_TPM_BIOS_LOG' or
something which selects ACPI?  We'll see what Rajiv thinks.

> As a separate issue, IMA requires the TPM driver to be compiled in
> (not loaded as a module) so it is available at IMA initialization, and
> the driver apparently requires ACPI in this case. I believe Rajiv
> will comment more on this.

I know it's required to be built in.  Didn't know that required ACPI,
but if so, that's a good reason to push this to the TPM code and get it
out of the IMA code....

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