Hi Sughosh,
On Tue, 20 Jul 2021 at 07:32, Sughosh Ganu sughosh.ganu@linaro.org wrote:
hi Simon,
On Tue, 20 Jul 2021 at 18:20, Ilias Apalodimas ilias.apalodimas@linaro.org wrote:
Hi Simon, On Tue, 20 Jul 2021 at 15:33, Simon Glass sjg@chromium.org wrote:
Hi Ilias,
On Sat, 17 Jul 2021 at 08:27, Ilias Apalodimas ilias.apalodimas@linaro.org wrote:
The capsule signature is now part of our DTB. This is problematic when a user is allowed to change/fixup that DTB from U-Boots command line since he can overwrite the signature as well.
Just to repeat my question since it looks like I didn't get a response on the last patch:
Do you mean with the 'fdt' command?
If you mean the FDT fixups, they happen to a different DT, the one being passed to Linux.
In some platforms the key is derived from the relocated DTB, which we can overwrite. But I'll let Sughosh who figured it out explain the details.
On platforms where the dtb is concatenated with the u-boot image, using CONFIG_OF_SEPARATE, the fdt is also getting relocated to the main memory. We retrieve the public key from this dtb. By default, the fdtcontroladdr env variable is getting set to this relocated dtb address -- this address can also be accessed using the bdinfo command. Thus the public key can be modified before attempting the capsule update. Which is the reason why Ilias is moving the public key to the embedded rodata section.
You should be clearer about what problem you are trying to solve. Are you worried about a script changing the DT? Or just it being writable in general?
U-Boot itself is relocated also, including the rodata. So are you using the public key from the original location? What if that is not accessible after relocation?
There is also the 'fdt addr -c' command to find the control DT. It is not expected to be written to though. So just protect the memory to which it is relocated, or relocate it to a place that you can protect.
If the DT is writable it will affect U-Boot's operation, since that is where all the config is stored. There is no point in pretending that pulling one thing out of it and protecting it will result in any sort of improvement. This needs to be done properly.
Regards, Simon