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From: Mimi Zohar <zohar@linux.ibm.com>
To: david.safford@gmail.com,
	Janne Karhunen <janne.karhunen@gmail.com>,
	linux-integrity@vger.kernel.org,
	linux-security-module <linux-security-module@vger.kernel.org>
Cc: Ken Goldman <kgold@linux.ibm.com>,
	monty.wiseman@ge.com, Amir Goldstein <amir73il@gmail.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v2] ima: export the measurement list when needed
Date: Wed, 12 Feb 2020 20:03:16 -0500
Message-ID: <1581555796.8515.130.camel@linux.ibm.com> (raw)
In-Reply-To: <6b787049b965c8056d0e27360e2eaa8fa2f38b35.camel@gmail.com>

On Wed, 2020-02-12 at 16:08 -0500, david.safford@gmail.com wrote:
> On Tue, 2020-02-11 at 18:10 -0500, Mimi Zohar wrote:
> > On Tue, 2020-02-11 at 11:10 -0500, david.safford@gmail.com wrote:
> 
> > > <snip>
> > > 
> > This new feature will require setting up some infrastructure for
> > storing the partial measurement list(s) in order to validate a TPM
> > quote.  Userspace already can save partial measurement list(s) without
> > any kernel changes.  The entire measurement list does not need to be
> > read each time.  lseek can read past the last record previously read.
> >  The only new aspect is truncating the in kernel measurement list in
> > order to free kernel memory.
> 
> This is a pretty important new feature.
> A lot of people can't use IMA because of the memory issue.
> Also, I really think we need to let administrators choose the tradeoffs
> of keeping the list in memory, on a local file, or only on the 
> attestation server, as best fits their use cases.

Dave, I understand that some use cases require the ability of
truncating the measurement list.  We're discussing how to truncate the
measurement list.  For example, in addition to the existing securityfs
binary_runtime_measurements file, we could define a new securityfs
file indicating the number of records to delete.

> > 
> > < snip> 
> > 
> > Until there is proof that the measurement list can be exported to a
> > file before kexec, instead of carrying the measurement list across
> > kexec, and a TPM quote can be validated after the kexec, there isn't a
> > compelling reason for the kernel needing to truncate the measurement
> > list.
> 
> If this approach doesn't work with all the kexec use cases, then it is 
> useless, and the ball is in my court to prove that it does. Fortunately
> I have to test that anyway for the coming TLV support.
> 
> Working on it...

Testing could be done independently of the TLV support.  To verify
that you aren't loosing any measurements, boot with a measurement
policy like "ima_policy=tcb" on the boot command line.

thanks,

Mimi


  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200108111743.23393-1-janne.karhunen@gmail.com>
     [not found] ` <CAE=NcrZrbRinOAbB+k1rjhcae3nqfJ8snC_EnY8njMDioM7=vg@mail.gmail.com>
2020-02-06 14:13   ` Mimi Zohar
2020-02-10  8:04     ` Janne Karhunen
2020-02-10 15:26       ` Mimi Zohar
2020-02-10 18:18     ` david.safford
2020-02-10 20:24       ` Mimi Zohar
2020-02-11  8:06         ` Janne Karhunen
2020-02-11 16:10         ` david.safford
2020-02-11 23:10           ` Mimi Zohar
2020-02-12 21:08             ` david.safford
2020-02-13  1:03               ` Mimi Zohar [this message]
2020-02-13  6:41                 ` Janne Karhunen
2020-02-18 15:36                   ` Mimi Zohar

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