linux-kernel - Re: [PATCH v7 2/4] powerpc: Refactor kexec functions to move arch independent code to ima

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Message-ID: <9712c6bd-b0f8-773f-0b54-828410c61f50@linux.microsoft.com>
Date:   Wed, 21 Oct 2020 09:20:30 -0700
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>, bauerman@...ux.ibm.com,
        robh@...nel.org, gregkh@...uxfoundation.org, james.morse@....com,
        catalin.marinas@....com, sashal@...nel.org, will@...nel.org,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        robh+dt@...nel.org, frowand.list@...il.com,
        vincenzo.frascino@....com, mark.rutland@....com,
        dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com,
        pasha.tatashin@...een.com, allison@...utok.net,
        kstewart@...uxfoundation.org, takahiro.akashi@...aro.org,
        tglx@...utronix.de, masahiroy@...nel.org, bhsharma@...hat.com,
        mbrugger@...e.com, hsinyi@...omium.org, tao.li@...o.com,
        christophe.leroy@....fr
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, prsriva@...ux.microsoft.com,
        balajib@...ux.microsoft.com
Subject: Re: [PATCH v7 2/4] powerpc: Refactor kexec functions to move arch
 independent code to ima

On 10/20/20 8:50 PM, Mimi Zohar wrote:
> Hi Lakshmi,
> 
> On Tue, 2020-10-20 at 19:38 -0700, Lakshmi Ramasubramanian wrote:
>> On 10/20/20 1:01 PM, Mimi Zohar wrote:
>>> On Wed, 2020-09-30 at 13:59 -0700, Lakshmi Ramasubramanian wrote:
>>>> The functions ima_get_kexec_buffer() and ima_free_kexec_buffer(),
>>>> that handle carrying forward the IMA measurement logs on kexec for
>>>> powerpc do not have architecture specific code, but they are currently
>>>> defined for powerpc only.
>>>>
>>>> Move ima_get_kexec_buffer() and ima_free_kexec_buffer() to IMA
>>>> subsystem. A later patch in this series will use these functions for
>>>> carrying forward the IMA measurement log for ARM64.
>>>>
>>>> With the above refactoring arch/powerpc/kexec/ima.c contains only
>>>> functions used when CONFIG_IMA_KEXEC is enabled. Update Makefile
>>>> in arch/powerpc/kexec to include arch/powerpc/kexec/ima.c only
>>>> when CONFIG_IMA_KEXEC is enabled.
>>>>
>>>> Move ima_dump_measurement_list() and ima_add_kexec_buffer() to
>>>> a new file namely ima_kexec_fdt.c in IMA. Update
>>>> security/integrity/ima/Makefile to include ima_kexec_fdt.c only
>>>> when CONFIG_IMA_KEXEC is enabled.
>>>>
>>>> Co-developed-by: Prakhar Srivastava <prsriva@...ux.microsoft.com>
>>>> Signed-off-by: Prakhar Srivastava <prsriva@...ux.microsoft.com>
>>>> Signed-off-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
>>>
>>> The existing support for carrying the IMA measurement list across kexec
>>> is limited to powerpc.  This patch set is adding similar support for
>>> arm64, making as much of the existing code as generic as possible.
>>> However ima_dump_measurement_list() is already generic, but for some
>>> reason this patch moves it to ima_kexec_fdt.c.  ima_kexec_fdt.c should
>>> be limited to device tree specific code.
>>
>> I wanted to split the functions defined under CONFIG_HAVE_IMA_KEXEC and
>> CONFIG_IMA_KEXEC to separate files so that we can get rid of #ifdef in C
>> file and instead conditionally compile the C files (using Makefile).
>>
>> ima_dump_measurement_list() need to be defined only when
>> CONFIG_IMA_KEXEC is defined. I moved it to ima_kexec_fdt.c
> 
> In this case, everything in ima_kexec.c relates to carrying or
> restoring the measurement list.  It's a logical unit.  Separating them
> doesn't make sense.
> 

Sounds good - I'll keep ima_dump_measurement_list() and 
ima_add_kexec_buffer() in ima_kexec.c as it was earlier.

>>
>> Instead of ima_kexec_fdt.c, where ima_dump_measurement_list() and
>> ima_add_kexec_buffer() are defined, perhaps I can change the file name
>> to "ima_kexec_buffer.c". Would that be better?
> 
> I don't understand why adding support for carrying the IMA measurement
> across kexec on ARM64, should require any changes in the IMA loading
> and restoring the measurement list code itself.  Please minimize the
> changes.

Agreed - will do.

thanks,
  -lakshmi