linux-kernel - Re: [PATCH v5 0/5] Lazy flush for the auth session

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Message-ID: <3fed38bc5c9de9e1a16fd5c1413ba8a965d26dac.camel@linux.ibm.com>
Date: Tue, 01 Oct 2024 14:10:02 -0400
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, linux-integrity@...r.kernel.org
Cc: James.Bottomley@...senPartnership.com, roberto.sassu@...wei.com,
        mapengyu@...il.com, David Howells <dhowells@...hat.com>,
        Paul Moore
 <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn"
 <serge@...lyn.com>, Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe
 <jgg@...pe.ca>, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/5] Lazy flush for the auth session

On Sun, 2024-09-22 at 20:51 +0300, Jarkko Sakkinen wrote:
> On Sat Sep 21, 2024 at 3:08 PM EEST, Jarkko Sakkinen wrote:
> > This patch set aims to fix:
> > https://bugzilla.kernel.org/show_bug.cgi?id=219229.
> > 
> > The baseline for the series is the v6.11 tag.
> > 
> > v4:
> > https://lore.kernel.org/linux-integrity/20240918203559.192605-1-jarkko@kernel.org/
> > v3:
> > https://lore.kernel.org/linux-integrity/20240917154444.702370-1-jarkko@kernel.org/
> > v2:
> > https://lore.kernel.org/linux-integrity/20240916110714.1396407-1-jarkko@kernel.org/
> > v1:
> > https://lore.kernel.org/linux-integrity/20240915180448.2030115-1-jarkko@kernel.org/
> > 
> > Jarkko Sakkinen (5):
> >   tpm: Return on tpm2_create_null_primary() failure
> >   tpm: Implement tpm2_load_null() rollback
> >   tpm: flush the null key only when /dev/tpm0 is accessed
> >   tpm: Allocate chip->auth in tpm2_start_auth_session()
> >   tpm: flush the auth session only when /dev/tpm0 is open
> > 
> >  drivers/char/tpm/tpm-chip.c       |  14 ++++
> >  drivers/char/tpm/tpm-dev-common.c |   8 +++
> >  drivers/char/tpm/tpm-interface.c  |  10 ++-
> >  drivers/char/tpm/tpm2-cmd.c       |   3 +
> >  drivers/char/tpm/tpm2-sessions.c  | 109 ++++++++++++++++++------------
> >  include/linux/tpm.h               |   2 +
> >  6 files changed, 102 insertions(+), 44 deletions(-)
> 
> 
> Roberto, James, speaking of digest cache. This patch set has no aim to
> fix those issues but I do believe that it should improve also that 
> feature.
> 
> If I don't get soon patch reviews for the patch set, I'll pick the 2nd
> best option: disable bus encryption on all architectures including x86
> and ARM64 (being by default on).
> 
> It's a force majeure situation. I know this would sort out the issue
> but I really cannot send these as a pull request with zero reviewe-by's.
> 
> I expect this to be closed by tomorrow.

Jarkko, sorry to be so late to this discussion.  The bus HMAC/encryption really
impacts IMA as well.  Even with this patch set, it's slow.  My preference would
be to disable bus encryption on all architectures until there is a boot/runtime
option allowing it to be disabled for IMA as discussed in the other thread.

In the other thread, I also mentioned that the Kconfig is incorrectly worded. 
The performance degradation is not limited to encryption, but the HMAC itself. 
Please change "Saying Y here adds some encryption overhead to all kernel to TPM
transactions." to "Saying Y here adds overhead to all kernel to TPM
transactions."

thanks,

Mimi