linux-kernel - Re: [PATCH] security: Fix IMA Kconfig for dependencies on ARM64

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Date:   Wed, 07 Mar 2018 11:08:39 -0800
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jiandi An <anjiandi@...eaurora.org>
Cc:     dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com,
        linux-integrity@...r.kernel.org,
        linux-ima-devel@...ts.sourceforge.net,
        linux-ima-user@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] security: Fix IMA Kconfig for dependencies on ARM64

On Wed, 2018-03-07 at 13:55 -0500, Mimi Zohar wrote:
> On Wed, 2018-03-07 at 11:51 -0700, Jason Gunthorpe wrote:
> > 
> > On Tue, Mar 06, 2018 at 11:26:26PM -0600, Jiandi An wrote:
> > > 
> > > TPM_CRB driver is the TPM support for ARM64.  If it
> > > is built as module, TPM chip is registered after IMA
> > > init.  tpm_pcr_read() in IMA driver would fail and
> > > display the following message even though eventually
> > > there is TPM chip on the system:
> > > 
> > > ima: No TPM chip found, activating TPM-bypass! (rc=-19)
> > > 
> > > Fix IMA Kconfig to select TPM_CRB so TPM_CRB driver is
> > > built in kernel and initializes before IMA driver.
> > > 
> > > Signed-off-by: Jiandi An <anjiandi@...eaurora.org>
> > >  security/integrity/ima/Kconfig | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/security/integrity/ima/Kconfig
> > > b/security/integrity/ima/Kconfig
> > > index 35ef693..6a8f677 100644
> > > +++ b/security/integrity/ima/Kconfig
> > > @@ -10,6 +10,7 @@ config IMA
> > >  	select CRYPTO_HASH_INFO
> > >  	select TCG_TPM if HAS_IOMEM && !UML
> > >  	select TCG_TIS if TCG_TPM && X86

Well, this explains why IMA doesn't work on one of my X86 systems: it's
got a non i2c infineon TPM.

> > > +	select TCG_CRB if TCG_TPM && ACPI
> > >  	select TCG_IBMVTPM if TCG_TPM && PPC_PSERIES
> > >  	help
> > >  	  The Trusted Computing Group(TCG) runtime Integrity
> > 
> > This seems really weird, why are any specific TPM drivers linked to
> > IMA config, we have lots of drivers..
> > 
> > I don't think I've ever seen this pattern in Kconfig before?
> 
> As you've seen by the current discussions, the TPM driver needs to be
> initialized prior to IMA.  Otherwise IMA goes into TPM-bypass mode.
>  That implies that the TPM must be builtin to the kernel, and not as
> a kernel module.

Actually, that's not necessarily true:  If we don't begin appraisal
until after the initrd phase, then the initrd can load TPM modules
before IMA starts.

This would involve a bit of code rejigging to not require a TPM until
IMA wants to write its first measurement, but it looks doable and would
get us out of having to second guess TPM selections.

James