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

From: prsriva <[email-masked]>
Date: Tue, 24 Sep 2019 12:54:26 -0700

On 9/19/19 8:07 PM, Thiago Jung Bauermann wrote:
> Hello Prakhar,
>
> Prakhar Srivastava <[email-masked]> 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 <[email-masked]>
>> ---
>>   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
>
> _______________________________________________
> linux-arm-kernel mailing list
> [email-masked]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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