[PATCH RFC] image: apply FDTOs on FDT image node without a load property

[Marek Vasut]

On 12/19/24 4:03 PM, Quentin Schulz wrote:
> From: Quentin Schulz <quentin.schulz at cherry.de>
> 
> A FIT image which is NOT using -E when created by mkimage - that is with
> image data within the FIT - will fail to apply FDTO if the base FDT
> image node does not specify a load property (which points to an address
> in DRAM). This is because we check that the FDT address we want to apply
> overlay to (i.e. modify and likely increase in size) is not inside the
> FIT and give up otherwise. This is assumed necessary because we may then
> overwrite other data when applying in-place.
> 
> However, we can do better than giving up: relocating the FDT in another
> place in DRAM where it's safe to increase its size and apply FDTOs.
> 
> Suggested-by: Marek Vasut <marex at denx.de>
> Signed-off-by: Quentin Schulz <quentin.schulz at cherry.de>
> ---
> Tested with extlinux with:
> - conf node with multiple fdt entries
> - conf node with base fdt + conf node with fdto (stored in fdt property)
> - FDT image node with load property (behavior unchanged)
> - FDT image node without load property
> 
> I'll be frank, I don't really know what I'm doing here and I'm on
> holidays for a month in a few hours, so take this with a bigger grain of
> salt than usual (hence the RFC). It works (tm) for now.
> 
> Cc: Heiko Stuebner <heiko at sntech.de>
> ---
>   boot/image-fit.c | 17 +++++++++++------
>   1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/boot/image-fit.c b/boot/image-fit.c
> index 7d56f0b5e6ed39a75e029b09dc95d605835c0f91..088482c4d5d2e194cce66f10b0acd9e586f826b2 100644
> --- a/boot/image-fit.c
> +++ b/boot/image-fit.c
> @@ -2392,13 +2392,18 @@ int boot_get_fdt_fit(struct bootm_headers *images, ulong addr,
>   	image_end = addr + fit_get_size(fit);
>   	/* verify that relocation took place by load address not being in fit */
>   	if (load >= image_start && load < image_end) {

This has to be updated to handle the mkimage -E case too. Basically, if 
the FDT is outside of the fitImage tree area, but still in the trailing 
blob area at the end of fitImage generated with mkimage -E, then any 
modification to the DT which would result in resize may either fail or 
corrupt the surrounding blobs.

The safe but heavy handed option would be to relocate unconditionally .

> -		/* check is simplified; fit load checks for overlaps */
> -		printf("Overlayed FDT requires relocation\n");
> -		fdt_noffset = -EBADF;
> -		goto out;
> -	}
> +		/* Cannot overlay an FDT stored inside the fitImage, so let's relocate */
> +		char *of_flat_tree = map_sysmem(load, len);
>   
> -	base = map_sysmem(load, len);
> +		len = ALIGN(fdt_totalsize(load), SZ_4K);
> +		if (boot_relocate_fdt(&of_flat_tree, &len)) {

Please print the error value in case of failure here, it is useful for 
debugging.

> +			printf("Required FDT relocation for applying overlays failed...");
> +			fdt_noffset = -EBADF;
> +			goto out;
> +		}
> +
> +		load = (ulong)of_flat_tree;
> +	}