Re: [PATCH] FIT: Address Secure Boot Bypass for Signed FIT Images

[Sascha Hauer <s.hauer@pengutronix.de>]

Hi Tom,

On Mon, Mar 02, 2026 at 04:09:37PM -0600, Tom Rini wrote:
> There is a flaw in how U-Boot verifies and generates signatures for FIT
> images. To prevent mix and match style attacks, it is recommended to
> use signed configurations. How this is supposed to work is documented in
> doc/usage/fit/signature.rst.
> 
> Crucially, the `hashed-nodes` property of the `signature` node contains
> which nodes of the FIT device tree were hashed as part of the signature
> and should be verified. However, this property itself is not part of the
> hash and can therefore be modified by an attacker. Furthermore, the
> signature only contains the name of each node and not the path in the
> device tree to the node.
> 
> This patch reworks the code to address this specific oversight.

As this breaks compatibility between old U-Boot and new FIT images and
the other way round it would be good to introduce a version field to FIT
images. With that at least newer U-Boot versions could print a more
meaningful error message than just "image verification failed" which
gives no clue what had actually happened.

Sascha

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