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

[Lakshmi Ramasubramanian]

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