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From:   Thiago Jung Bauermann <bauerman@linux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Cc:     Mimi Zohar <zohar@linux.ibm.com>, robh@kernel.org,
        takahiro.akashi@linaro.org, gregkh@linuxfoundation.org,
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Subject: Re: [PATCH v13 2/6] powerpc: Move arch independent ima kexec
 functions to drivers/of/kexec.c
In-reply-to: <71764175-4007-2828-f882-9215c062330a@linux.microsoft.com>
Date:   Tue, 22 Dec 2020 21:40:32 -0300
Message-ID: <878s9pl5hb.fsf@manicouagan.localdomain>
MIME-Version: 1.0
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Lakshmi Ramasubramanian <nramas@linux.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.

-- 
Thiago Jung Bauermann
IBM Linux Technology Center