Re: [RFC PATCH v1 1/1] Add support for arm64 to carry ima measurement log in kexec_file_load

[prsriva]

On 9/19/19 8:07 PM, Thiago Jung Bauermann wrote:
> Hello Prakhar,
>
> Prakhar Srivastava <prsriva@xxxxxxxxxxxxxxxxxxx> writes:
>
> > During kexec_file_load, carrying forward the ima measurement log allows
> > a verifying party to get the entire runtime event log since the last
> > full reboot since that is when PCRs were last reset.
> >
> > Signed-off-by: Prakhar Srivastava <prsriva@xxxxxxxxxxxxxxxxxxx>
> > ---
> >   arch/arm64/Kconfig                     |   7 +
> >   arch/arm64/include/asm/ima.h           |  29 ++++
> >   arch/arm64/include/asm/kexec.h         |   5 +
> >   arch/arm64/kernel/Makefile             |   3 +-
> >   arch/arm64/kernel/ima_kexec.c          | 213 +++++++++++++++++++++++++
> >   arch/arm64/kernel/machine_kexec_file.c |   6 +
> >   6 files changed, 262 insertions(+), 1 deletion(-)
> >   create mode 100644 arch/arm64/include/asm/ima.h
> >   create mode 100644 arch/arm64/kernel/ima_kexec.c
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 3adcec05b1f6..f39b12dbf9e8 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -976,6 +976,13 @@ config KEXEC_VERIFY_SIG
> >   	  verification for the corresponding kernel image type being
> >   	  loaded in order for this to work.
> >
> > +config HAVE_IMA_KEXEC
> > +	bool "Carry over IMA measurement log during kexec_file_load() syscall"
> > +	depends on KEXEC_FILE
> > +	help
> > +	  Select this option to carry over IMA measurement log during
> > +	  kexec_file_load.
> > +
> >   config KEXEC_IMAGE_VERIFY_SIG
> >   	bool "Enable Image signature verification support"
> >   	default y
> This is not right. As it stands, HAVE_IMA_KEXEC is essentially a synonym
> for IMA_KEXEC.
>
> It's not meant to be user-visible in the config process. Instead, it's
> meant to be selected by the arch Kconfig (probably by the ARM64 config
> symbol) to signal to IMA's Kconfig that it can offer the IMA_KEXEC
> option.
>
> I also mentioned in my previous review that config HAVE_IMA_KEXEC should
> be defined in arch/Kconfig, not separately in both arch/arm64/Kconfig
> and arch/powerpc/Kconfig.

I see the entry exists in arch/Kconfig and is overwritten.
I will remove entries both from powerpc and arm64.

How do i cross-compile for powerpc?

> > diff --git a/arch/arm64/include/asm/ima.h b/arch/arm64/include/asm/ima.h
> > new file mode 100644
> > index 000000000000..e23cee84729f
> > --- /dev/null
> > +++ b/arch/arm64/include/asm/ima.h
> > @@ -0,0 +1,29 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef _ASM_ARM64_IMA_H
> > +#define _ASM_ARM64_IMA_H
> > +
> > +struct kimage;
> > +
> > +int ima_get_kexec_buffer(void **addr, size_t *size);
> > +int ima_free_kexec_buffer(void);
> > +
> > +#ifdef CONFIG_IMA
> > +void remove_ima_buffer(void *fdt, int chosen_node);
> > +#else
> > +static inline void remove_ima_buffer(void *fdt, int chosen_node) {}
> > +#endif
> I mentioned in my previous review that remove_ima_buffer() should exist
> even if CONFIG_IMA isn't set. Did you arrive at a different conclusion?

I made the needed changed in makefile, missed removing the

configs here. Thanks for pointing this out.

> > +
> > +#ifdef CONFIG_IMA_KEXEC
> > +int arch_ima_add_kexec_buffer(struct kimage *image, unsigned long load_addr,
> > +			      size_t size);
> > +
> > +int setup_ima_buffer(const struct kimage *image, void *fdt, int chosen_node);
> > +#else
> > +static inline int setup_ima_buffer(const struct kimage *image, void *fdt,
> > +				   int chosen_node)
> > +{
> > +	remove_ima_buffer(fdt, chosen_node);
> > +	return 0;
> > +}
> > +#endif /* CONFIG_IMA_KEXEC */
> > +#endif /* _ASM_ARM64_IMA_H */
> > diff --git a/arch/arm64/kernel/ima_kexec.c b/arch/arm64/kernel/ima_kexec.c
> > new file mode 100644
> > index 000000000000..b14326d541f3
> > --- /dev/null
> > +++ b/arch/arm64/kernel/ima_kexec.c
> In the previous patch, you took the powerpc file and made a few
> modifications to fit your needs. This file is now somewhat different
> than the powerpc version, but I don't understand to what purpose. It's
> not different in any significant way.
>
> Based on review comments from your previous patch, I was expecting to
> see code from the powerpc file moved to an arch-independent part of the
> the kernel and possibly adapted so that both arm64 and powerpc could use
> it. Can you explain why you chose this approach instead? What is the
> advantage of having superficially different but basically equivalent
> code in the two architectures?
>
> Actually, there's one change that is significant: instead of a single
> linux,ima-kexec-buffer property holding the start address and size of
> the buffer, ARM64 is now using two properties (linux,ima-kexec-buffer
> and linux,ima-kexec-buffer-end) for the start and end addresses. In my
> opinion, unless there's a good reason for it Linux should be consistent
> accross architectures when possible.
>
> --
> Thiago Jung Bauermann
> IBM Linux Technology Center
>
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