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

[Lakshmi Ramasubramanian]

On 12/22/20 4:40 PM, Thiago Jung Bauermann wrote:
> Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx> 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