u-boot environement writing is always enabled regardless of force_ro value

[zahir]

On my platform, the u-boot environment variables can always be modified. Currently, I'm changing the value of `force_ro` to '1', which sets the permission mode to read-only. This change is reflected in the output of the `lsblk` command. However, even after rebooting my device, I can still write values to my boot partition, and the changes persist.

Here are the results of my test:

$ cat /sys/block/mmcblk0boot1/force_ro
1
$ fw_setenv primary 2
$ fw_printenv primary
2

Here are some details about my platform:

•  Cross Compiler: Yocto EL40(Kirkstone)
•  Bootloader: u-boot
•  U-boot Source: git://github.com/nxp-imx/uboot-imx.git;protocol=https
•  U-boot Source Branch: lf_v2022.04
•  `fw_setenv` and `fw_printenv` package version in Yocto: libubootenv_0.3.2

Hardware details:

•  System Architecture: arm
•  CPU: armv8
•  SoC: imx8m

Could anyone suggest a solution to make my boot partition read-only based on the value of `force_ro`?

[Sanket_Parekh · Accepted solution]

Hi @zahir,

I hope you are doing well.

From looking at the source code of libubootenv (source code of fw_printenv & fw_setenv), It seems that the force_ro flag doesn't really protect the boot partition write from fw_setenv. 

Please refer to file_write() function in libubootenv/src/uboot_env.c, which will call fileprotect(dev, false) to enable write access(by writing '0' to force_ro) and fileprotect(dev, true) at end to disable write access again.

handle protected mmcblk_boot_ devices

I hope it helps!

Could anyone suggest a solution to make my boot partition read-only based on the value of `force_ro`?
If this is truly required then one needs to make changes in the source code of libubootenv.

Thanks & Regards,
Sanket Parekh

[zahir]

@Sanket_Parekh Yes you are right about the libubootenv , which bypasses the force_ro write protection by the mentioned commit. So for my platform, I have to modify the source code 

Thanks for your quick replay and valid root cause trace