[systemd-devel] Fedora 38 and signed PCR binding

[Aleksandar Kostadinov]

On Thu, Oct 12, 2023 at 1:14 AM Dan Streetman <ddstreet at ieee.org> wrote:
> On Sun, Oct 8, 2023 at 8:09 AM Aleksandar Kostadinov <akostadi at redhat.com> wrote:
> ...
> > Here's what I did:
> > > sudo systemd-cryptenroll --wipe-slot=tpm2 --tpm2-device=auto --tpm2-public-key-pcrs=11 /dev/sda3
>
> This probably isn't what you want, because you're specifying
> --tpm2-public-key-pcrs= but not --tpm2-public-key=, so the
> --tpm2-public-key-pcrs= doesn't actually do anything (it should
> probably either fail or at least print a warning).

in man pages I see:
--tpm2-public-key= option accepts a path to a PEM encoded RSA
           public key, to bind the encryption to. If this is not specified
           explicitly, but a file tpm2-pcr-public-key.pem exists in one of the
           directories /etc/systemd/, /run/systemd/, /usr/lib/systemd/
           (searched in this order), it is automatically used.

I do have such a file.

> Since you didn't specify --tpm2-pcrs=, it will default to use only
> PCR7, using the current value (at the time you ran
> systemd-cryptenroll).

I specify --tpm2-public-key-pcrs=11, should I specify also
--tpm2-pcrs? I don't want to bind to plain PCRs.

> Just for testing, can you try:
> sudo systemd-cryptenroll --tpm2-device=auto --tpm2-pcrs="" /dev/sda3
>
> That will enroll your tpm with *no* pcr values, so it should always
> successfully unlock your volume using the tpm (note, you probably
> don't want to do this other than for testing). Then see if it uses the
> tpm to unlock the volume on boot. If so, you just need to get the
> specific PCR parameters correct (and make sure to supply your PEM
> public key to systemd-cryptenroll using --tpm2-public-key=), and
> provide the correct signature.

This is a nice check actually. And in fact it does not open the volume
automatically. Which is super strange. As it worked with the normal
grub based boot process.

sudo systemd-cryptenroll --wipe-slot=tpm2 --tpm2-device=auto
--tpm2-pcrs= /dev/sda3
then removed `tpm2-measure-pcr=yes` from /etc/crypttab, then
`dracut-f` and finally `ukify ..` with the exact same arguments as
before.

Did I miss something?

Strange is that in `journalctl -b` I still see "Couldn't find
signature for this PCR bank, PCR index and public key." So I wonder
what could be broken and how to fix it. How to inspect the initrd
inside the UKI?

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