Arch Linux

OlivK

Member

Registered: 2017-10-15

Posts: 22

Enable to find root with custom kernel.

Hi all,

I tried to compile my own kernel following the instruction in Kernel/Arch Build System.

For the first trial I did not change any config options. I just changed the name of the package in PKGBUILD:

pkgbase=linux-custom

I build the initramfs with a custom preset file /etc/mkinitcpio.d/linux-custom.preset:

  ALL_kver="/boot/vmlinuz-linux-custom"
  PRESETS=('default')
  default_config="/etc/mkinitcpio.conf"
  default_image="/boot/initramfs-linux-custom.img"

And run mkinitcpio -p linux-custom.

When I boot the kernel load, I see logs showing that udev is loaded, etc... but it seems it does not find the root UUID, that should be decrypted. I tried to get a shell with busybox but when I press keyboard nothing happen, it is as if my keyboard were not plugged.

So I tried an other way. I just changed nothing in the package, not even the package name. I compiled this home built linux package and replaced the upstream package by this one. With this home built kernel everything run fine but I get tens of messages

PKCS#7 signature not signed with a trusted key

during the boot process.
                                                                                                                                                                                                [SOLVED]

Last edited by OlivK (2019-01-29 09:32:13)

loqs

Member

Registered: 2014-03-06

Posts: 17,363

Re: Enable to find root with custom kernel.

https://git.archlinux.org/svntogit/pack … b952d4e55d
https://www.kernel.org/doc/Documentatio … igning.rst

OlivK

Member

Registered: 2017-10-15

Posts: 22

Re: Enable to find root with custom kernel.

https://git.archlinux.org/svntogit/pack … b952d4e55d
https://www.kernel.org/doc/Documentatio … igning.rst

According to what I had read the key is automatically generated, and modules signed with it.

Maybe mkinitcpio does not load the modules built with the custom kernel? I could I check it?

loqs

Member

Registered: 2014-03-06

Posts: 17,363

Re: Enable to find root with custom kernel.

You could check with modinfo if the modules have been signed.

OlivK

Member

Registered: 2017-10-15

Posts: 22

Re: Enable to find root with custom kernel.

They all have a signature... and whatever the build, the signature is always the same.

OlivK

Member

Registered: 2017-10-15

Posts: 22

Re: Enable to find root with custom kernel.

I do not understand, whatever the module the command `modinfo module_file_name` showes the same signature.

OlivK

Member

Registered: 2017-10-15

Posts: 22

Re: Enable to find root with custom kernel.

I can't believe it, all the modules are signed with a private key that is publicly available on the git source directory!

progandy

Member

Registered: 2012-05-17

Posts: 5,192

Re: Enable to find root with custom kernel.

I can't believe it, all the modules are signed with a private key that is publicly available on the git source directory!

Where do you get that idea? The key is only generated locally in your build directory.

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OlivK

Member

Registered: 2017-10-15

Posts: 22

Re: Enable to find root with custom kernel.

I got this idea while I was looking at the output of `modinfo <module_file_name>` all modules have the same signature, for all builds. What is that signature?

Last edited by OlivK (2019-01-28 20:13:21)

loqs

Member

Registered: 2014-03-06

Posts: 17,363

Re: Enable to find root with custom kernel.

Was the src directory cleaned between builds?

progandy

Member

Registered: 2012-05-17

Posts: 5,192

Re: Enable to find root with custom kernel.

As long as you reuse the source directory from the last build without cleaning it up, the key stays the same.

Edit: Forgot to reload ...

Last edited by progandy (2019-01-28 20:31:31)

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| alias CUTF='LANG=en_XX.UTF-8@POSIX ' |

OlivK

Member

Registered: 2017-10-15

Posts: 22

Re: Enable to find root with custom kernel.

Yes I erase all directories loaded during the makepkg process before recompiling.

Actually I had checked only the first bytes of the signature. I am sorry, I would like to understand why those first bytes are always the same, but whatsoever this is not the problem.

I checked the signature of few installed modules using the script in https://unix.stackexchange.com/question … -signature, and actualy every signature are fine (also in the extracted initramfs). Actualy the trouble came from a customization of mine. I have changed /etc/mkinitcpio.d/linux.preset and when I reinstalled my own linux package, this file was override, and the image was not placed in the expected directory. So I used the wrong init ram disk. So I fixed the last problem which was that when I compile myself the linux package I had this signature error message.

But I still have trouble with my original problem which is that the boot process start but it cannot find my root device if I compile use a package named linux-custom. So I am rebuilding the package linux-custom and I am going to retry from start. I will make a new post when I will have finished that.

OlivK

Member

Registered: 2017-10-15

Posts: 22

Re: Enable to find root with custom kernel.

Finaly I was using the wrong kernel image when building the efi file.

Thank you for your help.