Re: [PATCH 08/13] ARM: am625: support hash verification of full barebox

[Marco Felsch <m.felsch@pengutronix.de>]

On 25-02-28, Sascha Hauer wrote:
> This implements the necessary SoC code to check the full barebox against
> a sha256 compiled into the first stage barebox.
> 
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> ---
>  arch/arm/mach-k3/Kconfig |  1 +
>  arch/arm/mach-k3/r5.c    | 14 ++++++++++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/arch/arm/mach-k3/Kconfig b/arch/arm/mach-k3/Kconfig
> index 50919dc7e3..561ad1dac4 100644
> --- a/arch/arm/mach-k3/Kconfig
> +++ b/arch/arm/mach-k3/Kconfig
> @@ -16,6 +16,7 @@ config MACH_K3_CORTEX_R5
>  	select ELF
>  	select K3_DDRSS
>  	select FIP
> +	select HAVE_FIRMWARE_VERIFY_NEXT_IMAGE
>  	depends on 32BIT
>  	select ARM_USE_COMPRESSED_DTB
>  	default y
> diff --git a/arch/arm/mach-k3/r5.c b/arch/arm/mach-k3/r5.c
> index e12c888afa..cb52ff364d 100644
> --- a/arch/arm/mach-k3/r5.c
> +++ b/arch/arm/mach-k3/r5.c
> @@ -248,6 +248,8 @@ static int load_fip(const char *filename, off_t offset)
>  {
>  	struct fip_state *fip;
>  	struct fip_image_desc *desc;
> +	unsigned char shasum[SHA256_DIGEST_SIZE];
> +	int ret;
>  
>  	fip = fip_image_open(filename, offset);
>  	if (IS_ERR(fip)) {
> @@ -255,6 +257,18 @@ static int load_fip(const char *filename, off_t offset)
>  		return PTR_ERR(fip);
>  	}
>  
> +	if (IS_ENABLED(CONFIG_FIRMWARE_VERIFY_NEXT_IMAGE)) {
> +		ret = fip_sha256(fip, shasum);
> +		if (ret) {
> +			pr_err("Cannot calc fip sha256: %pe\n", ERR_PTR(ret));
> +			return ret;
> +		}
> +
> +		ret = firmware_next_image_verify(shasum, SHA256_DIGEST_SIZE, true);
> +		if (ret)
> +			return ret;

Albeit it would involve way more effort, I would like to see that the
FIP image format does have support for signatures within their "struct
image_desc" for each image.
This way it would be far easier for us to verify each image separately
and in a common way. Also it wouldn't require to rebuild the "r5"
tiboot3.bin to include the the updated sha256sum each time.

I do see why we can't use the externa-firmware mechanism now but I
wouldn't call it firmware_next_image_verify(). Maybe limit the scope to
fip and extent it later or remove/deprecate it once we managed to add
signatures to the FIP format.
Also the shasum size seems like the user would have a choice to choose
other sha-sums which he hasn't, therefore I would drop it.

Regards,
  Marco

> +	}
> +
>  	fip_for_each_desc(fip, desc) {
>  		struct fip_toc_entry *toc_entry = &desc->image->toc_e;
>  
> 
> -- 
> 2.39.5
> 
> 
>