Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <7a347c8f2a76fc80551a3dfcb66b0eec9b024a90.camel@linux.ibm.com>
Subject: Re: [PATCH v13 2/6] powerpc: Move arch independent ima kexec
 functions to drivers/of/kexec.c
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
        bauerman@linux.ibm.com, robh@kernel.org,
        takahiro.akashi@linaro.org, gregkh@linuxfoundation.org,
        will@kernel.org, catalin.marinas@arm.com, mpe@ellerman.id.au
Cc:     james.morse@arm.com, sashal@kernel.org, benh@kernel.crashing.org,
        paulus@samba.org, frowand.list@gmail.com,
        vincenzo.frascino@arm.com, mark.rutland@arm.com,
        dmitry.kasatkin@gmail.com, jmorris@namei.org, serge@hallyn.com,
        pasha.tatashin@soleen.com, allison@lohutok.net,
        masahiroy@kernel.org, bhsharma@redhat.com, mbrugger@suse.com,
        hsinyi@chromium.org, tao.li@vivo.com, christophe.leroy@c-s.fr,
        prsriva@linux.microsoft.com, balajib@linux.microsoft.com,
        linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org
Date:   Tue, 22 Dec 2020 14:45:05 -0500
In-Reply-To: <e0d9398b-1b46-8115-7bf0-28e9826fcd6b@linux.microsoft.com>
References: <20201219175713.18888-1-nramas@linux.microsoft.com>
         <20201219175713.18888-3-nramas@linux.microsoft.com>
         <a1a4526c0759eb3b5d70fb8edc89360718376def.camel@linux.ibm.com>
         <e0d9398b-1b46-8115-7bf0-28e9826fcd6b@linux.microsoft.com>
Content-Type: text/plain; charset="ISO-8859-15"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Precedence: bulk

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.

Mimi