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

[Tom Rini]

On Wed, Mar 04, 2026 at 08:31:46AM +0100, Sascha Hauer wrote:
> 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.

It's not the first time we've had a break in backwards compatibility but
previously we had at least printed something about it specifically.

-- 
Tom
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