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From:   Thiago Jung Bauermann <bauerman@linux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Cc:     zohar@linux.ibm.com, robh@kernel.org, gregkh@linuxfoundation.org,
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Subject: Re: [PATCH v4 5/5] arm64: Add IMA kexec buffer to DTB
In-reply-to: <20200819172134.11243-6-nramas@linux.microsoft.com>
Date:   Fri, 28 Aug 2020 18:43:19 -0300
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Lakshmi Ramasubramanian <nramas@linux.microsoft.com> writes:

> The address and size of the current kernel's IMA measurement log
> need to be added to the device tree's IMA kexec buffer node for
> the log to be carried over to the next kernel on the kexec call.
>
> Add the IMA measurement log buffer properties to the device tree for
> ARM64. Update CONFIG_KEXEC_FILE to select CONFIG_HAVE_IMA_KEXEC to
> indicate that the IMA measurement log information is present in
> the device tree.
>
> Co-developed-by: Prakhar Srivastava <prsriva@linux.microsoft.com>
> Signed-off-by: Prakhar Srivastava <prsriva@linux.microsoft.com>
> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
> ---
>  arch/arm64/Kconfig                     |  1 +
>  arch/arm64/kernel/machine_kexec_file.c | 11 +++++++++++
>  2 files changed, 12 insertions(+)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 6d232837cbee..9f03c8245e5b 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1077,6 +1077,7 @@ config KEXEC
>  config KEXEC_FILE
>  	bool "kexec file based system call"
>  	select KEXEC_CORE
> +	select HAVE_IMA_KEXEC
>  	help
>  	  This is new version of kexec system call. This system call is
>  	  file based and takes file descriptors as system call argument
> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> index 4c54723e7a04..8488f8e87d1a 100644
> --- a/arch/arm64/kernel/machine_kexec_file.c
> +++ b/arch/arm64/kernel/machine_kexec_file.c
> @@ -153,6 +153,17 @@ static int setup_dtb(struct kimage *image,
>  				FDT_PROP_KASLR_SEED);
>  	}
>  
> +	/* add ima-kexec-buffer */
> +	if (image->arch.ima_buffer_size > 0) {
> +
> +		ret = fdt_appendprop_addrrange(dtb, 0, off,
> +				FDT_PROP_IMA_KEXEC_BUFFER,
> +				image->arch.ima_buffer_addr,
> +				image->arch.ima_buffer_size);
> +		if (ret)
> +			return (ret == -FDT_ERR_NOSPACE ? -ENOMEM : -EINVAL);
> +	}
> +
>  	/* add rng-seed */
>  	if (rng_is_initialized()) {
>  		void *rng_seed;

I believe you need to add a memory reservation to the dtb covering the
IMA kexec buffer, otherwise nothing stops the new kernel from stomping
over it. E.g., powerpc does:

	ret = fdt_add_mem_rsv(fdt, image->arch.ima_buffer_addr,
			      image->arch.ima_buffer_size);

-- 
Thiago Jung Bauermann
IBM Linux Technology Center