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

[Mimi Zohar]

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