linux-kernel - Re: [PATCH v8 2/7] kexec: define functions to map and unmap segments

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Message-ID: <55acf768b52b47dd9d33fa0486772d8c7ae38779.camel@linux.ibm.com>
Date: Thu, 27 Feb 2025 10:41:38 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Baoquan He <bhe@...hat.com>, steven chen <chenste@...ux.microsoft.com>
Cc: stefanb@...ux.ibm.com, roberto.sassu@...weicloud.com,
        roberto.sassu@...wei.com, eric.snowberg@...cle.com,
        ebiederm@...ssion.com, paul@...l-moore.com, code@...icks.com,
        bauermann@...abnow.com, linux-integrity@...r.kernel.org,
        kexec@...ts.infradead.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, madvenka@...ux.microsoft.com,
        nramas@...ux.microsoft.com, James.Bottomley@...senpartnership.com,
        vgoyal@...hat.com, dyoung@...hat.com,
        Mike Rapoport <mike.rapoport@...il.com>
Subject: Re: [PATCH v8 2/7] kexec: define functions to map and unmap segments

[Cc'ing Mike Rapoport]

On Mon, 2025-02-24 at 14:14 +0800, Baoquan He wrote:
> Hi Steve, Mimi,
> 
> On 02/18/25 at 02:54pm, steven chen wrote:
> > Currently, the mechanism to map and unmap segments to the kimage
> > structure is not available to the subsystems outside of kexec.  This
> > functionality is needed when IMA is allocating the memory segments
> > during kexec 'load' operation.  Implement functions to map and unmap
> > segments to kimage.
> 
> I am done with the whole patchset understanding. My concern is if this
> TPM PCRs content can be carried over through newly introduced KHO. I can
> see that these patchset doesn't introduce too much new code changes,
> while if many conponents need do this, kexec reboot will be patched all
> over its body and become ugly and hard to maintain.
> 
> Please check Mike Rapoport's v4 patchset to see if IMA can register
> itself to KHO and do somthing during 2nd kernel init to restore those
> TPM PCRs content to make sure all measurement logs are read correctly.
> [PATCH v4 00/14] kexec: introduce Kexec HandOver (KHO)

Hi Baoquan,

I was hoping to look at Mike's patch set before responding, but perhaps it is
better to respond earlier rather than later with my initial thoughts.

The IMA measurement list isn't stored in contiguous memory, but has to be
marshalled before being carried across kexec, and then unmarshalled to restore
it after the kexec.  Roberto Sassu has been thinking about changing how the IMA
measurement list is stored so marshalling/unmarshalling wouldn't be necessary. 
Making both this change and using KHO going forward would be a good idea.

However, that sort of change wouldn't be appropriate to backport.  So the
question comes down to whether being unable to attest the measurement list,
because the measurements are copied too early at kexec load, but the TPM is
being extended through kexec exec, is considered a bug.  If that is the case,
then I suggest finish cleaning up and upstreaming this patch set so that it
could be backported.

thanks,

Mimi