On 1/11/23 01:13, Heiko Schocher wrote:
> Hello Sean,
>
> Thanks for your answer!
>
> On 10.01.23 17:27, Sean Anderson wrote:
>> On 1/10/23 08:18, Heiko Schocher wrote:
>>> Hello Simon,
> [...]
>>> While writting this email ... in [3] the line
>>>
>>> require = "conf"
>>>
>>> poped into my eyes .... and in fit_image_verify_required_sigs() there is
>>> check:
>>>
>>> if (!required || strcmp(required, "image"))
>>> continue;
>>>
>>> and yes! changing in [3]
>>>
>>> -required = "conf";
>>> +required = "image";
>>>
>>> makes sourcing the signed script working (error in case of no
>>> signature or wrong signature)! ... but booting the signed fitimage
>>> now breaks ... so it seems, I cannot use configuration signing with
>>> images signing ?
>>>
>>> I tried to add two key nodes in signature node of u-boot dtb ... one with
>>> require = "conf" and one with require = "image" ... but no luck...
>>>
>>> Also adding a configurations section to scripts its file did not helped
>>> (which will not prevent the problem sourcing a not signed script)
>>
>> As you discovered, you must either have required = "image", in which case
>>
>> source :
>>
>> will be secure. Otherwise, you must use
>>
>> source \#
>>
>> Any other way is not secure.
>
> My "hack" checks a configuration signature in fitimage with script in it...
> so also "secure" ...
>
> BTW: why we need a env variable to enable checking in cmd/source.c?
> I would say, if verify fit images is enabled we always should check
> signature ... but this is another question...
I think it's to allow disabling things for debugging. If the variable
does not exist, it defaults to verifying.
> So I tried your suggestion:
>
> => tftp 100000 script.bin.signed;setenv verify 1;source \#100000
> Speed: 1000, full duplex
> Using ethernet@24000 device
> TFTP from server 192.168.3.1; our IP address is 192.168.3.40
> Filename 'script.bin.signed'.
> Load address: 0x100000
> Loading: #
> 233.4 KiB/s
> done
> Bytes transferred = 1679 (68f hex)
> ## Executing script at 00000000
> Wrong image format for "source" command
> =>
>
> same for
>
> => source \#100000:script-1
> ## Executing script at 00000000
> Wrong image format for "source" command
> =>
>
> Which is the error message from the switch in image_source_script()
> from cmd/source.c ...
Right.
What kind of image is your script? Do you have CONFIG_FIT (and *only*
CONFIG_FIT) enabled?
> (check if fitimage "is okay"):
> => source 100000
> ## Executing script at 00100000
> sha256+ sha256,rsa2048:dev+ Hallo from script
> => source 100000:script-1
> ## Executing script at 00100000
> sha256+ sha256,rsa2048:dev+ Hallo from script
> => source 100000:script-2
> ## Executing script at 00100000
> Can't find 'script-2' FIT subimage
> =>
>
> and changing hash in fitimages signature leads to:
> => mw 1001c0 0 1
> => source 100000:script-1
> ## Executing script at 00100000
> sha256+ sha256,rsa2048:dev- Hallo from script
> =>
>
> As I described ... problem "hash is detected, but script is executed",
> as public key in u-boots dtb has required = "conf"; (as it is used also
> for fitimage boot, where we use conf signing)
>
> May you have an example (u-boot.dtb, its and complete working command
> for a signed fitimage script)?
$ cat << EOF >> dm-verity.its
/dts-v1/;
/ {
description = "dm-verity boot parameters";
#address-cells = <1>;
images {
dm-verity {
data = /incbin/("dm-verity.scr");
type = "script";
arch = "arm64";
compression = "none";
hash-1 {
algo = "sha256";
};
};
};
configurations {
default = "conf";
conf {
description = "Load dm-verity boot parameters";
script = "dm-verity";
signature {
algo = "sha256,rsa2048";
key-name-hint = "u-boot";
sign-images = "script";
};
};
};
};
EOF
$ uboot-mkimage -EB 0x40 -f dm-verity.its dm-verity.itb
$ uboot-mkimage -EB 0x40 -r -F -k /path/to/keys dm-verity.itb
> The main problem is (I think) that we check for fitimages which are
> used for booting kernels, a "signed configuration" and in fitimage for scripts
> only "image" signatures ... and a combination of both is not possible
> (except I also sign the image nodes in kernel fitimage too ... which
> than leads in checking configuration signature and image signature on
> boot... but may a way to go (and disabling hash check) ?
Yes, which is why you need to have # in the source command to force only
using configurations. IMO we should also check image-only FITs, but
Simon disagrees.
--Sean
