On Fri, Nov 13, 2020 at 07:50:38PM -0600, Glenn Washburn wrote: > On Fri, 13 Nov 2020 14:25:07 -0800 > James Bottomley <j...@linux.ibm.com> wrote: > > > v2: update geli.c to use conditional prompt and add callback for > > variable message printing and secret destruction > > > > To achieve encrypted disk images in the AMD SEV encrypted virtual > > machine, we need to add the ability for grub to retrieve the disk > > passphrase from the SEV launch secret. To do this, we've modified > > OVMF to set aside an area for the injected secret and pass up a > > configuration table for it: > > > > https://edk2.groups.io/g/devel/topic/78198617#67339 > > > > The patches in this series modify grub to look for the disk passphrase > > in the secret configuration table and use it to decrypt any disks in > > the system if they are found. This is so an encrypted image with a > > properly injected password will boot without any user intervention. > > > > The three patches firstly modify the cryptodisk consumers to allow > > arbitrary password getters instead of the current console based one. > > I like this idea in general. > > > The next patch adds a '-s' option to cryptodisk to allow it to use a > > saved password and the final one adds a sevsecret command to check for > > the secrets configuration table and provision the disk passphrase from > > it if an entry is found. > > I'm not in favor of this approach. This feels like a special case of > providing a key file to cryptomount. We have working (and I believe > merge worthy) patches for adding key file support. Unfortunately, due > to the current position in the grub development cycle, they have not > been merged. As a side note, it might be interesting to re-work the > key file patch series to use the arbitrary password getter mechanism > you've created.
Ah, should've read all messages first. I'm now repeating kind of the
same thing as a reply to patch 1/3.
> What I would prefer, because it feels more generic, is to have the
> sevsecret module create a procfs entry (perhaps (proc)/sevsecret),
> which outputs the secret data when read (or NULL string if some error
> in finding the secret). Then to cryptomount all devices that accept
> the sev secret do:
>
> cryptomount -a -k (proc)/sevsecret
Interesting approach. I think I tend to agree, but I'm not too sure
about potential security implications. Anyway, I still like the password
callback function per-se as it nicely deduplicates existing code
already. So regardless of where we end up here, I think that would be
nice to have anyway.
Patrick
> In this case you could re-use most of the code in
> grub_efi_sevsecret_find and creating the procfs entry would be trivial
> (see bottom of cryptodisk.c for an example on how to do this).
>
> One potential issue could be getting error messages from
> grub_efi_sevsecret_find back to the user and a solution could be to
> replace the grub_error with grub_dprintf("sev", ...) statements and set
> debug=sev unconditionally. In most cases no output would be
> generated, but some debug log messages should be generated on error.
>
> Also, if this series does end up adding an option to cryptomount, a
> documentation patch should be added. I think we should start
> documenting procfs paths as well.
>
> Also, out of curiosity, is it possible that there are multiple
> GRUB_EFI_DISKPASSWD_GUID entries defined? You only get the first one,
> but I'm wondering if the spec allows for more.
>
> > With all this in place, the sequence to boot
> > an encrypted volume without user intervention is:
> >
> > sevsecret
> > cryptomount -s
> > source (crypto0)/boot/grub.cfg
> >
> > Assuming there's a standard Linux root partition.
> >
> > James
>
> Glenn
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> https://lists.gnu.org/mailman/listinfo/grub-devel
signature.asc
Description: PGP signature
_______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
