FIT image verification not working on imx8mm

FIT image verification not working on imx8mm

[Michael Opdenacker]

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Greetings,

For a secure boot project on Toradex Verdin with imx8mm, I'm trying to 
enable FIT image signature verification in U-Boot.

Slava's "Generation of FIT images" presentation at the recent OE 
workshop has been very useful:
https://pretalx.com/media/openembedded-workshop-2026-2025/submissions/R8KJQZ/resources/_LJtpFTR.pdf

I generated a temporary local RSA 2048 key, and I'm using it to sign a 
FIT image.

I also set the UBOOT_SIGN_KEYDIR, UBOOT_SIGN_KEYNAME and 
UBOOT_SIGN_ENABLE variables to add the public key to U-Boot's DTB.

The signature indeed appears in the generated u-boot.dtb file, in a 
"/signature" node:

     signature {

         key-imx8mmsb {
             required = "conf";
             algo = "sha256,rsa2048";
             rsa,r-squared = <0x56bb2a2b 0xc6b322cc 0x2f828666 
0x75c8bc46 0xd13093af 0xc2244c35 0xb6420649 0x478d7ed3 0xeb7a0399 
0x3b1d49a9 0xc106169d 0x7328dbb4 0x2140c49b 0x111732a1 0xb3286fed 
0x53937163 0x8c28f85c 0xe272b1ee 0x5e009a53 0x13883205 0xcda0fbc7 
0xd7ed4e75 0x9ed065c1 0xb6ca1e69 0xf2c9dce2 0xcf8ebf7b 0x59a72b94 
0x501d2751 0x437e3355 0xcba6b07a 0x9b13feea 0x1032d715 0xab3cdd83 
0x319b6bb0 0xfc31ff93 0xb7fabbb6 0x79d5d0fa 0x9c0f76e0 0x3528c22e 
0xbbec6d6c 0x7981362f 0x528848a9 0xb57aa235 0x462ed577 0x4ccc8b9d 
0xeb4ce969 0x5fb085b3 0x3fced511 0xfd98edfe 0xf3a4ca51 0x1bb74370 
0x3a11c748 0xbbd5be95 0x946f8b3f 0x3d8c98b6 0x3b0e00a8 0xeca87fc6 
0x7331981e 0xaaee80df 0x476816f2 0x509aaab1 0xa5f50e1a 0x474d0de8 
0xc551ac97>;
             rsa,modulus = <0xb3ade247 0x4b8d0aef 0x4581e5e9 0x6084f135 
0x778847c7 0xaf23976f 0x81b6eb84 0xa2406db4 0x2b89e624 0x81f913c9 
0xd6ebef10 0x3e30adee 0xbca06cbe 0x5693b23b 0xc6b211f1 0xfea7a90d 
0x2767ca7c 0xaa8b2ddb 0xcf8a63ea 0x66fe8c59 0x43b34a2f 0x720009d8 
0xa2a61281 0x2f7fe049 0xfc3d10e5 0x1b52409 0xdeb52a16 0xa4e5fa78 
0x7116d181 0xc0c2f39e 0x24a626b4 0x7e59438b 0x6680b1f4 0xc4b1184c 
0x8bb65f34 0x92038fd7 0x3901c347 0xc2095158 0x3159031a 0xaa4bb76c 
0xc53f2009 0x9f4941f8 0x736ca84a 0xd83bd011 0x3685d02c 0x6f4cb5e7 
0xd07e8566 0x173819f 0x8f41366d 0x8b0f82fd 0x54c01fc0 0xc216cbd5 
0x2fc4a666 0x426ff669 0x880428ca 0x7c7615c 0xcdc97895 0x8c936a3c 
0xd6d7e82e 0x5bf63d9d 0x9fcd83a2 0xb131015f 0xc530c031 0x8446f707>;
             rsa,exponent = <0x00 0x10001>;
             rsa,n0-inverse = <0x93653949>;
             rsa,num-bits = <0x800>;
             key-name-hint = "imx8mmsb";
         };
     };

I also compiled U-Boot with
|CONFIG_FIT_SIGNATURE=y
|
However, when U-Boot loads the FIT image, it only checks the integrity 
of the sha256 hash of the FIT image parts:
    Verifying Hash Integrity ... sha256+ OK

No signature checking happens. I can also load an unsigned FIT image 
which is accepted too. Indeed, when I open the generated "imx-boot" file 
(or "flash.bin", linking to the same file) that is used to boot the 
board, I can see a DTB for my board, but it doesn't contain any 
"signature" node, unlike in "u-boot.dtb".

What could I be missing? My layer, along with a kas file to generate the 
image, is available on 
https://gitlab.com/rootcommit/meta-imx8mm-secureboot. I'm using the 
Toradex Easy Installer (Tezi) to flash the image on eMMC. My layer is 
relies on the "master" branches of the required layers, but I have the 
same problem on Scarthgap too.

Any suggestions are appreciated.
Thanks in advance
Michael.

-- 
Root Commit
Embedded Linux Training and Consulting
https://rootcommit.com

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Re: [yocto] FIT image verification not working on imx8mm

[Marco Cavallini]

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Hi Michael,
usually this is a bug caused by a missing option in u-boot.

Marco Cavallini
KOAN - Abinsula Group
Bergamo, Italia
https://KoanSoftware.com

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Re: FIT image verification not working on imx8mm

[Vyacheslav Yurkov]

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Hi Michael,
I believe the message is correct:

 > Verifying Hash Integrity ... sha256+ OK

The "+" sign means the signature verification succeeded. The "-" would 
mean otherwise.

I've just tried again to boot a fit image built without 
UBOOT_SIGN_ENABLE and got:

 > No 'signature' subnode found for '<NULL>' hash node in 'conf-my-dtb' 
config node

Do you use the u-boot as SPL by any chance?

Slava

On 21.02.2026 11:39, Michael Opdenacker wrote:
>
> Greetings,
>
> For a secure boot project on Toradex Verdin with imx8mm, I'm trying to 
> enable FIT image signature verification in U-Boot.
>
> Slava's "Generation of FIT images" presentation at the recent OE 
> workshop has been very useful:
> https://pretalx.com/media/openembedded-workshop-2026-2025/submissions/R8KJQZ/resources/_LJtpFTR.pdf
>
> I generated a temporary local RSA 2048 key, and I'm using it to sign a 
> FIT image.
>
> I also set the UBOOT_SIGN_KEYDIR, UBOOT_SIGN_KEYNAME and 
> UBOOT_SIGN_ENABLE variables to add the public key to U-Boot's DTB.
>
> The signature indeed appears in the generated u-boot.dtb file, in a 
> "/signature" node:
>
>     signature {
>
>         key-imx8mmsb {
>             required = "conf";
>             algo = "sha256,rsa2048";
>             rsa,r-squared = <0x56bb2a2b 0xc6b322cc 0x2f828666 
> 0x75c8bc46 0xd13093af 0xc2244c35 0xb6420649 0x478d7ed3 0xeb7a0399 
> 0x3b1d49a9 0xc106169d 0x7328dbb4 0x2140c49b 0x111732a1 0xb3286fed 
> 0x53937163 0x8c28f85c 0xe272b1ee 0x5e009a53 0x13883205 0xcda0fbc7 
> 0xd7ed4e75 0x9ed065c1 0xb6ca1e69 0xf2c9dce2 0xcf8ebf7b 0x59a72b94 
> 0x501d2751 0x437e3355 0xcba6b07a 0x9b13feea 0x1032d715 0xab3cdd83 
> 0x319b6bb0 0xfc31ff93 0xb7fabbb6 0x79d5d0fa 0x9c0f76e0 0x3528c22e 
> 0xbbec6d6c 0x7981362f 0x528848a9 0xb57aa235 0x462ed577 0x4ccc8b9d 
> 0xeb4ce969 0x5fb085b3 0x3fced511 0xfd98edfe 0xf3a4ca51 0x1bb74370 
> 0x3a11c748 0xbbd5be95 0x946f8b3f 0x3d8c98b6 0x3b0e00a8 0xeca87fc6 
> 0x7331981e 0xaaee80df 0x476816f2 0x509aaab1 0xa5f50e1a 0x474d0de8 
> 0xc551ac97>;
>             rsa,modulus = <0xb3ade247 0x4b8d0aef 0x4581e5e9 0x6084f135 
> 0x778847c7 0xaf23976f 0x81b6eb84 0xa2406db4 0x2b89e624 0x81f913c9 
> 0xd6ebef10 0x3e30adee 0xbca06cbe 0x5693b23b 0xc6b211f1 0xfea7a90d 
> 0x2767ca7c 0xaa8b2ddb 0xcf8a63ea 0x66fe8c59 0x43b34a2f 0x720009d8 
> 0xa2a61281 0x2f7fe049 0xfc3d10e5 0x1b52409 0xdeb52a16 0xa4e5fa78 
> 0x7116d181 0xc0c2f39e 0x24a626b4 0x7e59438b 0x6680b1f4 0xc4b1184c 
> 0x8bb65f34 0x92038fd7 0x3901c347 0xc2095158 0x3159031a 0xaa4bb76c 
> 0xc53f2009 0x9f4941f8 0x736ca84a 0xd83bd011 0x3685d02c 0x6f4cb5e7 
> 0xd07e8566 0x173819f 0x8f41366d 0x8b0f82fd 0x54c01fc0 0xc216cbd5 
> 0x2fc4a666 0x426ff669 0x880428ca 0x7c7615c 0xcdc97895 0x8c936a3c 
> 0xd6d7e82e 0x5bf63d9d 0x9fcd83a2 0xb131015f 0xc530c031 0x8446f707>;
>             rsa,exponent = <0x00 0x10001>;
>             rsa,n0-inverse = <0x93653949>;
>             rsa,num-bits = <0x800>;
>             key-name-hint = "imx8mmsb";
>         };
>     };
>
> I also compiled U-Boot with
> |CONFIG_FIT_SIGNATURE=y
> |
> However, when U-Boot loads the FIT image, it only checks the integrity 
> of the sha256 hash of the FIT image parts:
>    Verifying Hash Integrity ... sha256+ OK
>
> No signature checking happens. I can also load an unsigned FIT image 
> which is accepted too. Indeed, when I open the generated "imx-boot" 
> file (or "flash.bin", linking to the same file) that is used to boot 
> the board, I can see a DTB for my board, but it doesn't contain any 
> "signature" node, unlike in "u-boot.dtb".
>
> What could I be missing? My layer, along with a kas file to generate 
> the image, is available on 
> https://gitlab.com/rootcommit/meta-imx8mm-secureboot. I'm using the 
> Toradex Easy Installer (Tezi) to flash the image on eMMC. My layer is 
> relies on the "master" branches of the required layers, but I have the 
> same problem on Scarthgap too.
>
> Any suggestions are appreciated.
> Thanks in advance
> Michael.
>
> -- 
> Root Commit
> Embedded Linux Training and Consulting
> https://rootcommit.com

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Re: FIT image verification not working on imx8mm

[Michael Opdenacker]

Hi Slava,

Thanks a lot for having a look at this issue!

On 2/22/26 2:50 PM, Vyacheslav Yurkov wrote:
> Hi Michael,
> I believe the message is correct:
>
> > Verifying Hash Integrity ... sha256+ OK
>
> The "+" sign means the signature verification succeeded. The "-" would 
> mean otherwise.
>
> I've just tried again to boot a fit image built without 
> UBOOT_SIGN_ENABLE and got:
>
> > No 'signature' subnode found for '<NULL>' hash node in 'conf-my-dtb' 
> config node

I don't think that's the case, because if I replace my "fitImage" file 
by an unsigned one, it is still gladly accepted by U-Boot:

Verdin iMX8MM # load mmc 0:2 40000000 boot/fitImage
8426099 bytes read in 50 ms (160.7 MiB/s)
Verdin iMX8MM # bootm 40000000
## Loading kernel from FIT Image at 40000000 ...
    Using 'conf-imx8mm-syk-ccu.dtb' configuration
    Verifying Hash Integrity ... OK
    Trying 'kernel-1' kernel subimage
      Description:  Linux kernel
      Type:         Kernel Image
      Compression:  gzip compressed
      Data Start:   0x400000e8
      Data Size:    8347434 Bytes = 8 MiB
      Architecture: AArch64
      OS:           Linux
      Load Address: 0x48200000
      Entry Point:  0x48200000
      Hash algo:    sha256
      Hash value: 
  2dc1e494faaefa209b46b1b7aed7dbbbdb61de81b2770705e6cb9ef36c886435
    Verifying Hash Integrity ... sha256+ OK
## Loading fdt from FIT Image at 40000000 ...
    Using 'conf-imx8mm-syk-ccu.dtb' configuration
    Verifying Hash Integrity ... OK
    Trying 'fdt-imx8mm-syk-ccu.dtb' fdt subimage
      Description:  Flattened Device Tree blob
      Type:         Flat Device Tree
      Compression:  uncompressed
      Data Start:   0x407f6128
      Data Size:    76717 Bytes = 74.9 KiB
      Architecture: AArch64
      Load Address: 0x50200000
      Hash algo:    sha256
      Hash value: 
  3378b4f94a993a9bba8c60c50dd58acb57df6833926be34bfbcedd789687a436
    Verifying Hash Integrity ... sha256+ OK
    Loading fdt from 0x407f6128 to 0x50200000
    Booting using the fdt blob at 0x50200000
Working FDT set to 50200000
    Uncompressing Kernel Image to 48200000
    Loading Device Tree to 00000000bced4000, end 00000000bcee9bac ... OK
Working FDT set to bced4000

Starting kernel ...

>
> Do you use the u-boot as SPL by any chance?

Yes, U-Boot SPL runs right before U-Boot.
Cheers
Michael.

-- 
Root Commit
Embedded Linux Training and Consulting
https://rootcommit.com

Re: [yocto] FIT image verification not working on imx8mm

[Quentin Schulz]

Hi Michael,

On 2/22/26 5:07 PM, Michael Opdenacker via lists.yoctoproject.org wrote:
> Hi Slava,
> 
> Thanks a lot for having a look at this issue!
> 
> On 2/22/26 2:50 PM, Vyacheslav Yurkov wrote:
>> Hi Michael,
>> I believe the message is correct:
>>
>> > Verifying Hash Integrity ... sha256+ OK
>>
>> The "+" sign means the signature verification succeeded. The "-" would 
>> mean otherwise.
>>
>> I've just tried again to boot a fit image built without 
>> UBOOT_SIGN_ENABLE and got:
>>
>> > No 'signature' subnode found for '<NULL>' hash node in 'conf-my-dtb' 
>> config node
> 
> I don't think that's the case, because if I replace my "fitImage" file 
> by an unsigned one, it is still gladly accepted by U-Boot:
> 

You need to enforce signature verification such that a missing signature 
means you cannot boot proper, as far as I remember, this is NOT the default.

See the official documentation for FIT signature: 
https://docs.u-boot.org/en/latest/usage/fit/signature.html#public-key-storage

You need a "required" property (in your SPL DTB's public key node!!!) 
set to either conf or images. I believe the best practice for security 
is conf.

I also recommend triple checking your defconfig to make sure you cannot 
boot non-FIT images (e.g. legacy format) which would allow an attacker 
to bypass the signature mechanism even if enforced for FIT images.

Cheers,
Quentin

Re: [yocto] FIT image verification not working on imx8mm

[Francesco Valla]

Hi Michael,

On Sat, Feb 21, 2026 at 10:39:15AM +0000, Michael Opdenacker via lists.yoctoproject.org wrote:
> Greetings,
> 
> For a secure boot project on Toradex Verdin with imx8mm, I'm trying to
> enable FIT image signature verification in U-Boot.
> 
> Slava's "Generation of FIT images" presentation at the recent OE workshop
> has been very useful:
> https://pretalx.com/media/openembedded-workshop-2026-2025/submissions/R8KJQZ/resources/_LJtpFTR.pdf
> 
> I generated a temporary local RSA 2048 key, and I'm using it to sign a FIT
> image.
> 
> I also set the UBOOT_SIGN_KEYDIR, UBOOT_SIGN_KEYNAME and UBOOT_SIGN_ENABLE
> variables to add the public key to U-Boot's DTB.
> 
> The signature indeed appears in the generated u-boot.dtb file, in a
> "/signature" node:
> 
> � � signature {
> 
> � � � � key-imx8mmsb {
> � � � � � � required = "conf";
> � � � � � � algo = "sha256,rsa2048";
> � � � � � � rsa,r-squared = <0x56bb2a2b 0xc6b322cc 0x2f828666 0x75c8bc46
> 0xd13093af 0xc2244c35 0xb6420649 0x478d7ed3 0xeb7a0399 0x3b1d49a9 0xc106169d
> 0x7328dbb4 0x2140c49b 0x111732a1 0xb3286fed 0x53937163 0x8c28f85c 0xe272b1ee
> 0x5e009a53 0x13883205 0xcda0fbc7 0xd7ed4e75 0x9ed065c1 0xb6ca1e69 0xf2c9dce2
> 0xcf8ebf7b 0x59a72b94 0x501d2751 0x437e3355 0xcba6b07a 0x9b13feea 0x1032d715
> 0xab3cdd83 0x319b6bb0 0xfc31ff93 0xb7fabbb6 0x79d5d0fa 0x9c0f76e0 0x3528c22e
> 0xbbec6d6c 0x7981362f 0x528848a9 0xb57aa235 0x462ed577 0x4ccc8b9d 0xeb4ce969
> 0x5fb085b3 0x3fced511 0xfd98edfe 0xf3a4ca51 0x1bb74370 0x3a11c748 0xbbd5be95
> 0x946f8b3f 0x3d8c98b6 0x3b0e00a8 0xeca87fc6 0x7331981e 0xaaee80df 0x476816f2
> 0x509aaab1 0xa5f50e1a 0x474d0de8 0xc551ac97>;
> � � � � � � rsa,modulus = <0xb3ade247 0x4b8d0aef 0x4581e5e9 0x6084f135
> 0x778847c7 0xaf23976f 0x81b6eb84 0xa2406db4 0x2b89e624 0x81f913c9 0xd6ebef10
> 0x3e30adee 0xbca06cbe 0x5693b23b 0xc6b211f1 0xfea7a90d 0x2767ca7c 0xaa8b2ddb
> 0xcf8a63ea 0x66fe8c59 0x43b34a2f 0x720009d8 0xa2a61281 0x2f7fe049 0xfc3d10e5
> 0x1b52409 0xdeb52a16 0xa4e5fa78 0x7116d181 0xc0c2f39e 0x24a626b4 0x7e59438b
> 0x6680b1f4 0xc4b1184c 0x8bb65f34 0x92038fd7 0x3901c347 0xc2095158 0x3159031a
> 0xaa4bb76c 0xc53f2009 0x9f4941f8 0x736ca84a 0xd83bd011 0x3685d02c 0x6f4cb5e7
> 0xd07e8566 0x173819f 0x8f41366d 0x8b0f82fd 0x54c01fc0 0xc216cbd5 0x2fc4a666
> 0x426ff669 0x880428ca 0x7c7615c 0xcdc97895 0x8c936a3c 0xd6d7e82e 0x5bf63d9d
> 0x9fcd83a2 0xb131015f 0xc530c031 0x8446f707>;
> � � � � � � rsa,exponent = <0x00 0x10001>;
> � � � � � � rsa,n0-inverse = <0x93653949>;
> � � � � � � rsa,num-bits = <0x800>;
> � � � � � � key-name-hint = "imx8mmsb";
> � � � � };
> � � };
> 
> I also compiled U-Boot with
> |CONFIG_FIT_SIGNATURE=y
> |
> However, when U-Boot loads the FIT image, it only checks the integrity of
> the sha256 hash of the FIT image parts:
> � �Verifying Hash Integrity ... sha256+ OK
> 
> No signature checking happens. I can also load an unsigned FIT image which
> is accepted too. Indeed, when I open the generated "imx-boot" file (or
> "flash.bin", linking to the same file) that is used to boot the board, I can
> see a DTB for my board, but it doesn't contain any "signature" node, unlike
> in "u-boot.dtb".
> 
> What could I be missing? My layer, along with a kas file to generate the
> image, is available on https://gitlab.com/rootcommit/meta-imx8mm-secureboot.

(From what I can infer from the layer, since there are no explicit
dependencies declared, you are using meta-toradex-nxp, which in turn is
depending on meta-freescale. The idea/suggestion that follows starts
from this assumption, if your setup is different I may be totally
wrong.)

What is the value of the UBOOT_PROVIDES_BOOT_CONTAINER variable?

If it is 1 (as it might be, as meta-freescale sets it to 1 for imx8m*
SoCs if the bootloader is not u-boot-imx [0]), the imx-boot container
is generated by U-Boot using binman, which however iis / should not be
able to use the u-boot.dtb binary with the signature. The injection of
the signature in fact happens on the u-boot.dtb binary only after this
has been deployed [1], which in this case would be *after* the imx-boot
blob has been generated. 

> I'm using the Toradex Easy Installer (Tezi) to flash the image on eMMC. My
> layer is relies on the "master" branches of the required layers, but I have
> the same problem on Scarthgap too.
> 
> Any suggestions are appreciated.
> Thanks in advance
> Michael.
> 
> -- 
> Root Commit
> Embedded Linux Training and Consulting
> https://rootcommit.com

Regards,
Francesco


[0] https://github.com/Freescale/meta-freescale/blob/master/conf/machine/include/imx-base.inc#L108
[1] https://git.openembedded.org/openembedded-core/tree/meta/classes-recipe/uboot-sign.bbclass#n158

Re: [yocto] FIT image verification not working on imx8mm

[Michael Opdenacker]

Hi Francesco

Thanks for having a look at this issue and the corresponding code, much 
appreciated!

On 2/22/26 11:33 PM, Francesco Valla wrote:
> Hi Michael,
>
> On Sat, Feb 21, 2026 at 10:39:15AM +0000, Michael Opdenacker via lists.yoctoproject.org wrote:
>> Greetings,
>>
>> For a secure boot project on Toradex Verdin with imx8mm, I'm trying to
>> enable FIT image signature verification in U-Boot.
>>
>> Slava's "Generation of FIT images" presentation at the recent OE workshop
>> has been very useful:
>> https://pretalx.com/media/openembedded-workshop-2026-2025/submissions/R8KJQZ/resources/_LJtpFTR.pdf
>>
>> I generated a temporary local RSA 2048 key, and I'm using it to sign a FIT
>> image.
>>
>> I also set the UBOOT_SIGN_KEYDIR, UBOOT_SIGN_KEYNAME and UBOOT_SIGN_ENABLE
>> variables to add the public key to U-Boot's DTB.
>>
>> The signature indeed appears in the generated u-boot.dtb file, in a
>> "/signature" node:
>>
>>      signature {
>>
>>          key-imx8mmsb {
>>              required = "conf";
>>              algo = "sha256,rsa2048";
>>              rsa,r-squared = <0x56bb2a2b 0xc6b322cc 0x2f828666 0x75c8bc46
>> 0xd13093af 0xc2244c35 0xb6420649 0x478d7ed3 0xeb7a0399 0x3b1d49a9 0xc106169d
>> 0x7328dbb4 0x2140c49b 0x111732a1 0xb3286fed 0x53937163 0x8c28f85c 0xe272b1ee
>> 0x5e009a53 0x13883205 0xcda0fbc7 0xd7ed4e75 0x9ed065c1 0xb6ca1e69 0xf2c9dce2
>> 0xcf8ebf7b 0x59a72b94 0x501d2751 0x437e3355 0xcba6b07a 0x9b13feea 0x1032d715
>> 0xab3cdd83 0x319b6bb0 0xfc31ff93 0xb7fabbb6 0x79d5d0fa 0x9c0f76e0 0x3528c22e
>> 0xbbec6d6c 0x7981362f 0x528848a9 0xb57aa235 0x462ed577 0x4ccc8b9d 0xeb4ce969
>> 0x5fb085b3 0x3fced511 0xfd98edfe 0xf3a4ca51 0x1bb74370 0x3a11c748 0xbbd5be95
>> 0x946f8b3f 0x3d8c98b6 0x3b0e00a8 0xeca87fc6 0x7331981e 0xaaee80df 0x476816f2
>> 0x509aaab1 0xa5f50e1a 0x474d0de8 0xc551ac97>;
>>              rsa,modulus = <0xb3ade247 0x4b8d0aef 0x4581e5e9 0x6084f135
>> 0x778847c7 0xaf23976f 0x81b6eb84 0xa2406db4 0x2b89e624 0x81f913c9 0xd6ebef10
>> 0x3e30adee 0xbca06cbe 0x5693b23b 0xc6b211f1 0xfea7a90d 0x2767ca7c 0xaa8b2ddb
>> 0xcf8a63ea 0x66fe8c59 0x43b34a2f 0x720009d8 0xa2a61281 0x2f7fe049 0xfc3d10e5
>> 0x1b52409 0xdeb52a16 0xa4e5fa78 0x7116d181 0xc0c2f39e 0x24a626b4 0x7e59438b
>> 0x6680b1f4 0xc4b1184c 0x8bb65f34 0x92038fd7 0x3901c347 0xc2095158 0x3159031a
>> 0xaa4bb76c 0xc53f2009 0x9f4941f8 0x736ca84a 0xd83bd011 0x3685d02c 0x6f4cb5e7
>> 0xd07e8566 0x173819f 0x8f41366d 0x8b0f82fd 0x54c01fc0 0xc216cbd5 0x2fc4a666
>> 0x426ff669 0x880428ca 0x7c7615c 0xcdc97895 0x8c936a3c 0xd6d7e82e 0x5bf63d9d
>> 0x9fcd83a2 0xb131015f 0xc530c031 0x8446f707>;
>>              rsa,exponent = <0x00 0x10001>;
>>              rsa,n0-inverse = <0x93653949>;
>>              rsa,num-bits = <0x800>;
>>              key-name-hint = "imx8mmsb";
>>          };
>>      };
>>
>> I also compiled U-Boot with
>> |CONFIG_FIT_SIGNATURE=y
>> |
>> However, when U-Boot loads the FIT image, it only checks the integrity of
>> the sha256 hash of the FIT image parts:
>>     Verifying Hash Integrity ... sha256+ OK
>>
>> No signature checking happens. I can also load an unsigned FIT image which
>> is accepted too. Indeed, when I open the generated "imx-boot" file (or
>> "flash.bin", linking to the same file) that is used to boot the board, I can
>> see a DTB for my board, but it doesn't contain any "signature" node, unlike
>> in "u-boot.dtb".
>>
>> What could I be missing? My layer, along with a kas file to generate the
>> image, is available on https://gitlab.com/rootcommit/meta-imx8mm-secureboot.
> (From what I can infer from the layer, since there are no explicit
> dependencies declared, you are using meta-toradex-nxp, which in turn is
> depending on meta-freescale. The idea/suggestion that follows starts
> from this assumption, if your setup is different I may be totally
> wrong.)

I believe that's correct, from the kas file in the layer.
>
> What is the value of the UBOOT_PROVIDES_BOOT_CONTAINER variable?
>
> If it is 1 (as it might be, as meta-freescale sets it to 1 for imx8m*
> SoCs if the bootloader is not u-boot-imx [0]), the imx-boot container
> is generated by U-Boot using binman, which however iis / should not be
> able to use the u-boot.dtb binary with the signature. The injection of
> the signature in fact happens on the u-boot.dtb binary only after this
> has been deployed [1], which in this case would be *after* the imx-boot
> blob has been generated.
Indeed UBOOT_PROVIDES_BOOT_CONTAINER="1"
I'll study the corresponding code. Thanks again for your help!
Cheers
Michael.

Re: [yocto] FIT image verification not working on imx8mm

[Michael Opdenacker]

Hi Francesco, Quentin,

Thanks again for your help with this issue!

Some updates...

On 2/24/26 7:06 PM, Michael Opdenacker wrote:
> Hi Francesco
>
> Thanks for having a look at this issue and the corresponding code, 
> much appreciated!
>
> On 2/22/26 11:33 PM, Francesco Valla wrote:
>>
>> If it is 1 (as it might be, as meta-freescale sets it to 1 for imx8m*
>> SoCs if the bootloader is not u-boot-imx [0]), the imx-boot container
>> is generated by U-Boot using binman, which however iis / should not be
>> able to use the u-boot.dtb binary with the signature. The injection of
>> the signature in fact happens on the u-boot.dtb binary only after this
>> has been deployed [1], which in this case would be *after* the imx-boot
>> blob has been generated.


What you found out really helped, and I ultimately found that I'm 
supported to use the meta-toradex-security layer [1] which addresses 
this need [2], along with other aspects of secure boot.

So, I tried to use its "main" branch together with the latest OE layers. 
However, it turns out that Toradex only maintains their 
"scarthgap-7.x.y" branch at the moment [3]. So, I'll switch back to my 
original project on Scarthgap. If I understood correctly, I will have to:

- Inherit the "tdx-signed" global class
- Add this to my U-Boot recipe:

require recipes-bsp/u-boot/u-boot-fit-signature.inc

See 
https://github.com/toradex/meta-toradex-security/blob/scarthgap-7.x.y/recipes-bsp/u-boot/u-boot-fit-signature.inc 
for details.

This also automatically adds the needed config options to U-Boot:
https://github.com/toradex/meta-toradex-security/blob/scarthgap-7.x.y/recipes-bsp/u-boot/files/fit-signature.cfg

This corresponds to what you suggested, Quentin :)

I'll keep you posted.
Thanks again
Michael.

[1] https://github.com/toradex/meta-toradex-security
[2] 
https://github.com/toradex/meta-toradex-security/blob/scarthgap-7.x.y/docs/README-secure-boot.md
[3] https://github.com/toradex/meta-toradex-security/pull/161

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