Re: need help: patches to capture events between kexec load and execute

From: Mimi Zohar <zohar@linux.ibm.com>
To: Tushar Sugandhi <tusharsu@linux.microsoft.com>,
	Jonathan McDowell <noodles@fb.com>,
	bauermann@kolabnow.com
Cc: "kexec@lists.infradead.org" <kexec@lists.infradead.org>,
	Alasdair G Kergon <agk@redhat.com>,
	Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
	Tyler Hicks <tyhicks@linux.microsoft.com>,
	code@tyhicks.com
Subject: Re: need help: patches to capture events between kexec load and execute
Date: Wed, 31 May 2023 07:39:27 -0400	[thread overview]
Message-ID: <4eff26f794254c1f06ace12e68527fd3452ac47d.camel@linux.ibm.com> (raw)
In-Reply-To: <87775c1e-d1d3-519c-599b-30cdb1691cb2@linux.microsoft.com>

Hi Tushar,

On Thu, 2023-05-25 at 10:21 -0700, Tushar Sugandhi wrote:

> The issue of IMA measurements getting lost between kexec 'load' and 'execute' still exists. 
> I verified it on the mainline kernel 6.4.rc3. See *Appendix A* for details.
> 
> I went through Thiago's patches he wrote several years ago, and tried to develop a solution.
> 
> I was facing some issues with physical to virtual address translation. 
> One of my co-worker at Microsoft helped my re-write the logic which seems to be working.
> See the attached patch and *Appendix B* for details.
> 
> The basic functionality is working. I need to polish the code, and handle error paths in a better way.
> But before doing that, I need your feedback on the fundamental approach.
> Since I am not a kexec expert, it’d be great if I could get help with the code review
> and also suggestions on scenarios to test to validate the patch thoroughly. 
> Let me know if I should first post the patch as RFC on public forums for that.

Thanks, Tushar.   Measurements can and are currently being added to the
IMA measurement list between kexec load and execute, but are not being
carried across kexec.  These measurements also extend the TPM.  After
the soft reboot, without these additional measurements the IMA
measurement list cannot be verified against the TPM PCRs.

Your proposed patch, like Thiago's, saved the entire IMA measurement
list again.  Assuming the buffer size can't change between kexec load
and execute, as per the comment, why not just allocate the buffer on
kexec load and fill it on kexec exec?

To simulate the existing behavior, fill the buffer with as many
complete measurement records as the buffer will hold.

-- 
thanks,

Mimi

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