linux-kernel - Re: [PATCH v11 18/20] tpm: Add sysfs interface to allow setting and querying the default locality

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Message-ID: <685f3f00ddf88e961e2d861b7c783010774fe19d.camel@HansenPartnership.com>
Date: Fri, 01 Nov 2024 12:17:24 +0900
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Ross Philipson <ross.philipson@...cle.com>,
 linux-kernel@...r.kernel.org,  x86@...nel.org,
 linux-integrity@...r.kernel.org, linux-doc@...r.kernel.org, 
 linux-crypto@...r.kernel.org, kexec@...ts.infradead.org, 
 linux-efi@...r.kernel.org, iommu@...ts.linux-foundation.org
Cc: dpsmith@...rtussolutions.com, tglx@...utronix.de, mingo@...hat.com, 
 bp@...en8.de, hpa@...or.com, dave.hansen@...ux.intel.com, ardb@...nel.org, 
 mjg59@...f.ucam.org, peterhuewe@....de, jarkko@...nel.org, jgg@...pe.ca, 
 luto@...capital.net, nivedita@...m.mit.edu, herbert@...dor.apana.org.au, 
 davem@...emloft.net, corbet@....net, ebiederm@...ssion.com,
 dwmw2@...radead.org,  baolu.lu@...ux.intel.com, kanth.ghatraju@...cle.com,
 andrew.cooper3@...rix.com,  trenchboot-devel@...glegroups.com
Subject: Re: [PATCH v11 18/20] tpm: Add sysfs interface to allow setting and
 querying the default locality

On Fri, 2024-09-13 at 13:05 -0700, Ross Philipson wrote:
> Expose a sysfs interface to allow user mode to set and query the
> default locality set for the TPM chip.

What does a user need this for?  It somewhat conflicts with the idea of
running the kernel and user space TPM access in separate localities for
the purposes of key release, so we can seal keys to only release in the
kernel by policy.  When I last talked about this I thought we'd
probably use 0 for user and, say 2, for the kernel (mainly because
prior incarnations of this patch set seemed to access the TPM in
locality 2 from the kernel).  It really doesn't matter *what* locality
we use for the kernel and the user as long as it's known ahead of time
and the user can't gain access to the kernel locality.

Regards,

James