How to use vendor_dbx? - Githubissues

raddirad commented 1 year ago

Hi

I am currently opening an issue in the shim-review. Going through the README I saw the following

*******************************************************************************
### If you are re-using a previously used (CA) certificate, you will need to add the hashes of the previous GRUB2 binaries exposed to the CVEs to vendor_dbx in shim in order to prevent GRUB2 from being able to chainload those older GRUB2 binaries. If you are changing to a new (CA) certificate, this does not apply.
### Please describe your strategy.
*******************************************************************************

How do I compile a shim with a vendor_dbx file? How does this file have to look? Simply the hashes (sha256?) line by line?

We'd like to reuse the cert we have.

Regards

raddirad commented 1 year ago

is it

 hash-to-efi-sig-list ~/grubx64.efi vendor_dbx.esl

to generate the vendor_dbx

and then provide

 VENDOR_DBX_FILE=vendor_dbx.esl

as a make variable to compile the hashes into the shim dbx?

I better want to ask than submit and then waste time from the reviewer by doing something wrong.

Regards

tSU-RooT commented 2 months ago

Hi, this is humble my opinion.

is it

hash-to-efi-sig-list ~/grubx64.efi vendor_dbx.esl

to generate the vendor_dbx

I don't recommend to use hash-to-efi-sig-list, because this utility seems has a bug.[1] Recommend to use efisiglist or efisecdb (NOTE: efisiglist is removed after pesign version 114 2)

$ pesign --hash --padding --in <grub_binary_path>
hash: <hash>
$ efisiglist -o vendor_dbx.esl -a -h <hash>

Debian's package repository is awesome helpful for reference. https://salsa.debian.org/efi-team/shim/-/blob/master/debian/generate_dbx_list https://salsa.debian.org/efi-team/shim/-/blob/master/debian/debian-dbx.hashes

and then provide

VENDOR_DBX_FILE=vendor_dbx.esl

I think so. But actual setting depends how you build your shim(rpm, deb or else)

[1]: I have reported hash-to-efi-sig-list(efitools) behavior in help-grub mailing list, but some mysteries is not resolved still now. https://lists.gnu.org/archive/html/help-grub/2024-04/msg00018.html

rhboot / shim

How to use vendor_dbx? #544