[U-Boot] [PATCH] spl: implement CRC check on U-Boot uImage

[Wolfgang Denk]

Dear Simon,

In message <20181124124641.6605-1-simon.k.r.goldschmidt at gmail.com> you wrote:
> SPL currently does not check uImage CRCs when loading U-Boot.
> 
> This patch adds checking the uImage CRC when SPL loads U-Boot. It does
> this by reusing the existing config option SPL_CRC32_SUPPORT to allow
> leaving out the CRC check on boards where the additional code size or
> boot time is a problem (adding the CRC check currently adds ~1.4 kByte
> to flash).
> 
> The SPL_CRC32_SUPPORT config option now gets enabled by default if SPL
> support for legacy images is enabled to check the CRC on all boards
> that don't actively take countermeasures.

The new features is definitive useful, but I have a few comments.

First, I am not sure if mandatorily binding this feature to
SPL_CRC32_SUPPORT is a good idea? 

Might there not be reasons to have SPL_CRC32_SUPPORT enabled but
still wanting to keep the boot time minimal, and to intentionally NOT
check the CRC (similar to what setting "verify=no" would do)?
[This is commonly used when trading boot speed for reliability/securi-
ty...]

Second, may I please ask you to change the code such that the CRC is
checked "in-flight", i. e. while reading from the boot device and
writing it to the RAM, instead of re-reading the image from RAM?
Again, the reason is boot time. We will not reach a zero-copy boot,
but at least we should avoid an additional reading of what we just
wrote.  Yes, this would catch memory corruptions in RAM, but the
whole operation of U-Boot is based on the assumption that RAM is
working reliable and error-free. [If you drop this assumption, you
cannot guaranteee anything, i. e. you would have to fear that the
memory content might even get corrupted when reading it for the CRC
calculation - if you have such concerns, you should switch to
hardware with ECC RAM.]

Thanks!

Best regards,

Wolfgang Denk

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