Lakshmi Ramasubramanian [off-list ref] writes:

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On 12/22/20 11:45 AM, Mimi Zohar wrote:

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On Tue, 2020-12-22 at 10:53 -0800, Lakshmi Ramasubramanian wrote:

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On 12/22/20 6:26 AM, Mimi Zohar wrote:

Hi Mimi,

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On Sat, 2020-12-19 at 09:57 -0800, Lakshmi Ramasubramanian wrote:

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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.