[Buildroot] [Bug 15531] shim doesn't provide hooks for signing

From: bugzilla@busybox.net
To: buildroot@uclibc.org
Subject: [Buildroot] [Bug 15531] shim doesn't provide hooks for signing
Date: Tue, 11 Apr 2023 19:43:30 +0000	[thread overview]
Message-ID: <bug-15531-163-vlrVtQpakz@https.bugs.busybox.net/> (raw)
In-Reply-To: <bug-15531-163@https.bugs.busybox.net/>

https://bugs.busybox.net/show_bug.cgi?id=15531

Yann E. MORIN <yann.morin.1998@free.fr> changed:

           What    |Removed                     |Added
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                 CC|                            |yann.morin.1998@free.fr

--- Comment #1 from Yann E. MORIN <yann.morin.1998@free.fr> ---
Jonathan, All,

> Shim is supposed to provide a signed UEFI bootloader for secureboot.
> However, it is intended to be supplied with a key at build time (make
> VENDOR_CERT_FILE=<path.to.cer>).  Perhaps a menu option could be added
> to Config.in allowing the user to specify a certificate location.

As far as I understand it, this is two-fold:

1. shim can check the signature of the files it loads; this is what
    VENDOR_CERT_FILE is for, and

2. shim can be signed, so that the EFI bootrom can verify shim against
    known keys; this is what ENABLE_SHIM_CERT, if set, is for.

However, it is very possible to build a shim that is signed but does
not verify the signatures of what it loads, or the other way around.

So, we'd need two options:

1. BR2_TARGET_SHIM_CERT_FILE, the path to a .cer file, to set in
    VENDOR_CERT_FILE; if BR2_TARGET_SHIM_CERT_FILE, the generated shim
    will not check signatures of what it loads

2. BR2_TARGET_SHIM_SIGNED, a boolean to drive whether shim is signed,
    in which case the *.efi.signed should be installed, along with
    shim.key (so it can be enrolled into the UEFI bootloader?)

It looks like they are independent each from the other, and so can be
done in any order, and it is OK if you only send a patch for the one
you need (you'll send a patch, won't you? ;-) )

For 2, I am not sure if one can provide their own shim.key and shim.crt,
but looking at the Makefile, it looks like it should be possible (one
does not want to enroll a new key for each build!).

Regards,
Yann E. MORIN.

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