linux-kernel - Re: [PATCH v13 2/6] powerpc: Move arch independent ima kexec functions to drivers/of/kexec.c

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Message-ID: <71764175-4007-2828-f882-9215c062330a@linux.microsoft.com>
Date:   Tue, 22 Dec 2020 13:02:10 -0800
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>, bauerman@...ux.ibm.com,
        robh@...nel.org, takahiro.akashi@...aro.org,
        gregkh@...uxfoundation.org, will@...nel.org,
        catalin.marinas@....com, mpe@...erman.id.au
Cc:     james.morse@....com, sashal@...nel.org, benh@...nel.crashing.org,
        paulus@...ba.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,
        masahiroy@...nel.org, bhsharma@...hat.com, mbrugger@...e.com,
        hsinyi@...omium.org, tao.li@...o.com, christophe.leroy@....fr,
        prsriva@...ux.microsoft.com, balajib@...ux.microsoft.com,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v13 2/6] powerpc: Move arch independent ima kexec
 functions to drivers/of/kexec.c

On 12/22/20 11:45 AM, Mimi Zohar wrote:
> On Tue, 2020-12-22 at 10:53 -0800, Lakshmi Ramasubramanian wrote:
>> On 12/22/20 6:26 AM, Mimi Zohar wrote:
>>
>> Hi Mimi,
>>
>>>
>>> On Sat, 2020-12-19 at 09:57 -0800, Lakshmi Ramasubramanian wrote:
>>>>
>>>> diff --git a/arch/powerpc/kexec/Makefile b/arch/powerpc/kexec/Makefile
>>>> index 4aff6846c772..b6c52608cb49 100644
>>>> --- a/arch/powerpc/kexec/Makefile
>>>> +++ b/arch/powerpc/kexec/Makefile
>>>> @@ -9,13 +9,6 @@ obj-$(CONFIG_PPC32)		+= relocate_32.o
>>>>    
>>>>    obj-$(CONFIG_KEXEC_FILE)	+= file_load.o ranges.o file_load_$(BITS).o elf_$(BITS).o
>>>>    
>>>> -ifdef CONFIG_HAVE_IMA_KEXEC
>>>> -ifdef CONFIG_IMA
>>>> -obj-y				+= ima.o
>>>> -endif
>>>> -endif
>>>
>>> Notice how "kexec/ima.o" is only included if the architecture supports
>>> it and IMA is configured.  In addition only if CONFIG_IMA_KEXEC is
>>> configured, is the IMA measurement list carried across kexec.  After
>>> moving the rest of ima.c to drivers/of/kexec.c, this changes.   Notice
>>> how drivers/of/Kconfig includes kexec.o:
>>>
>>> obj-$(CONFIG_KEXEC_FILE) += kexec.o
>>>
>>> It is not dependent on CONFIG_HAVE_IMA_KEXEC.  Shouldn't all of the
>>> functions defined in ima.c being moved to kexec.o be defined within a
>>> CONFIG_HAVE_IMA_KEXEC ifdef?
>>>
>>
>> Thanks for reviewing the changes.
>>
>> In "drivers/of/kexec.c" the function remove_ima_buffer() is defined
>> under "#ifdef CONFIG_HAVE_IMA_KEXEC"
>>
>> setup_ima_buffer() is defined under "#ifdef CONFIG_IMA_KEXEC" - the same
>> way it was defined in "arch/powerpc/kexec/ima.c".
>>
>> As you know, CONFIG_IMA_KEXEC depends on CONFIG_HAVE_IMA_KEXEC (as
>> defined in "security/integrity/ima/Kconfig").
>>
>> ima_get_kexec_buffer() and ima_free_kexec_buffer() are unconditionally
>> defined in "drivers/of/kexec.c" even though they are called only when
>> CONFIG_HAVE_IMA_KEXEC is enabled. I will update these two functions to
>> be moved under "#ifdef CONFIG_HAVE_IMA_KEXEC"
> 
> The issue is the reverse.  CONFIG_HAVE_IMA_KEXEC may be enabled without
> CONFIG_IMA_KEXEC being enabled.  This allows the architecture to
> support carrying the measurement list across kexec, but requires
> enabling it at build time.
> 
> Only if CONFIG_HAVE_IMA_KEXEC is enabled should any of these functions
> be compiled at build.  This allows restoring the previous IMA
> measurement list, even if CONFIG_IMA_KEXEC is not enabled.
> 
> Only if CONFIG_IMA_KEXEC is enabled, should carrying the measurement
> list across kexec be enabled.  See how arch_ima_add_kexec_buffer,
> write_number, setup_ima_buffer are ifdef'ed in
> arch/powerpc/kexec/ima.c.
> 

Yes - I agree. I will make the following changes:

=> Enable the functions moved from "arch/powerpc/kexec/ima.c" to 
"drivers/of/kexec.c" only when CONFIG_HAVE_IMA_KEXEC is enabled.

=> Also, compile write_number() and setup_ima_buffer() only when 
CONFIG_IMA_KEXEC is enabled.

thanks,
  -lakshmi