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: <159c7e4d-0cad-158f-6f5b-9f3b60159b38@linux.microsoft.com>
Date:   Tue, 22 Dec 2020 21:03:05 -0800
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>, robh@...nel.org,
        takahiro.akashi@...aro.org, gregkh@...uxfoundation.org,
        will@...nel.org, catalin.marinas@....com, mpe@...erman.id.au,
        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 4:40 PM, Thiago Jung Bauermann wrote:
> 
> Lakshmi Ramasubramanian <nramas@...ux.microsoft.com> writes:
> 
>> 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.
> 
> Sounds good, with one additional change:
> 
> So far, CONFIG_HAVE_IMA_KEXEC was tested only in files that were built
> when CONFIG_IMA was set. With this series this is not the case anymore
> (in drivers/of/kexec.c). The simplest way to keep this consistent is to
> only enable CONFIG_HAVE_IMA_KEXEC if CONFIG_IMA is also set.
> 
> For example, with this:
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index e9f13fe08492..4ddd17215ecf 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -548,7 +548,7 @@ config KEXEC
>   config KEXEC_FILE
>   	bool "kexec file based system call"
>   	select KEXEC_CORE
> -	select HAVE_IMA_KEXEC
> +	select HAVE_IMA_KEXEC if IMA
>   	select BUILD_BIN2C
>   	select KEXEC_ELF
>   	depends on PPC64
> 
> And then the same thing on the arm64 patch.

This is a good idea Thiago - I will make this change in the Kconfig for 
both powerpc and arm64.

thanks,
  -lakshmi