Re: [PATCH 3/3] firmware: add external firmware PBL support

[Sascha Hauer <sha@pengutronix.de>]

On Mon, Aug 15, 2022 at 03:09:55PM +0200, Ahmad Fatoum wrote:
> Normally, barebox embds firmware into the binary referencing it, which
> means that device tree blobs, RAM training code and e.g. TF-A for i.MX8M
> end up in the prebootloader, while, e.g. Freescale FMan microcode ends
> up in barebox proper. The only exception so far was barebox proper:
> When only the PBL fits in on-chip SRAM, barebox proper is chainloaded
> from the boot medium. To avoid TOCTOU attack, it's read fully into DRAM
> after setup and then a SHA256 is calculated and compared against the
> hash embedded in barebox PBL, which in a secure boot system would be
> trusted by virtue of the PBL as a whole being verified beforehand by
> the BootROM.
> 
> Reuse this mechanism to support arbitrary firmware, which is now termed
> external firmware. Such firmware is placed beyond the piggydata (barebox
> proper) and only offset and hash are included in the prebootloader
> image. The new get_builtin_firmware_ext() is used to retrieve this
> external firmware after integrity verification with SHA256.

Does it make sense to use this mechanism for barebox proper as well?

>  #define get_builtin_firmware(name, start, size) \
>  	{							\
>  		extern char _fw_##name##_start[];		\
> @@ -65,4 +78,22 @@ void firmwaremgr_list_handlers(void);
>  		*size = _fw_##name##_end - _fw_##name##_start;	\
>  	}
>  
> +#define get_builtin_firmware_ext(name, base, start, size)		\

base is unused.

It would be nice if users could use the same macro for both internal and
external firmware, but I have no idea how and if this could be
implemented.

Sascha

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