linux-kernel - Re: [PATCH v3 0/5] kexec_file: Add buffer hand-over for the next kernel

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Date:   Thu, 25 Aug 2016 14:12:43 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
Cc:     kexec@...ts.infradead.org, linux-security-module@...r.kernel.org,
        linux-ima-devel@...ts.sourceforge.net,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        Dave Young <dyoung@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>, Baoquan He <bhe@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Eric Richter <erichte@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.com>
Subject: Re: [PATCH v3 0/5] kexec_file: Add buffer hand-over for the next
 kernel

On Thu, 25 Aug 2016 15:18:26 -0300 Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com> wrote:

> Hello,
> 
> This patch series implements a mechanism which allows the kernel to pass
> on a buffer to the kernel that will be kexec'd. This buffer is passed
> as a segment which is added to the kimage when it is being prepared
> by kexec_file_load.
> 
> How the second kernel is informed of this buffer is architecture-specific.
> On powerpc, this is done via the device tree, by checking
> the properties /chosen/linux,kexec-handover-buffer-start and
> /chosen/linux,kexec-handover-buffer-end, which is analogous to how the
> kernel finds the initrd.
> 
> This is needed because the Integrity Measurement Architecture subsystem
> needs to preserve its measurement list accross the kexec reboot. The
> following patch series for the IMA subsystem uses this feature for that
> purpose:
> 
> https://lists.infradead.org/pipermail/kexec/2016-August/016745.html
> 
> This is so that IMA can implement trusted boot support on the OpenPower
> platform, because on such systems an intermediary Linux instance running
> as part of the firmware is used to boot the target operating system via
> kexec. Using this mechanism, IMA on this intermediary instance can
> hand over to the target OS the measurements of the components that were
> used to boot it.
> 
> Because there could be additional measurement events between the
> kexec_file_load call and the actual reboot, IMA needs a way to update the
> buffer with those additional events before rebooting. One can minimize
> the interval between the kexec_file_load and the reboot syscalls, but as
> small as it can be, there is always the possibility that the measurement
> list will be out of date at the time of reboot.
> 
> To address this issue, this patch series also introduces
> kexec_update_segment, which allows a reboot notifier to change the
> contents of the image segment during the reboot process.
> 
> The last patch is not intended to be merged, it just demonstrates how
> this feature can be used.
> 
> This series applies on top of v6 of the "kexec_file_load implementation
> for PowerPC" patch series (which applies on top of v4.8-rc1):
> 
> https://lists.infradead.org/pipermail/kexec/2016-August/016960.html

I grabbed these two patch series.  I also merged the "IMA:
Demonstration code for kexec buffer passing." demonstration patch just
to get things a bit of testing.  I assume that once the "ima: carry the
measurement list across kexec" series has stabilised, I should drop the
demo patch and also grab those?  If so, pelase start cc'ing me.