Re: [PATCH v19 29/33] diskfilter: look up cryptodisk devices first

[Gary Lin]

On Wed, Oct 16, 2024 at 06:19:33PM +0200, Daniel Kiper wrote:
> On Fri, Sep 06, 2024 at 05:11:21PM +0800, Gary Lin via Grub-devel wrote:
> > When using disk auto-unlocking with TPM 2.0, the typical grub.cfg may
> > look like this:
> >
> >   tpm2_key_protector_init --tpm2key=(hd0,gpt1)/boot/grub2/sealed.tpm
> 
> s/grub2/grub/
> 
> >   cryptomount -u <PART-UUID> -P tpm2
> >   search --fs-uuid --set=root <FS-UUID>
> >
> > Since the disk search order is based on the order of module loading, the
> > attacker could insert a malicious disk with the same FS-UUID root to
> > trick grub2 to boot into the malicious root and further dump memory to
> 
> s/grub2/GRUB/ and below please...

Will fix them in the next version.

Gary Lin
> 
> > steal the unsealed key.
> >
> > Do defend against such an attack, we can specify the hint provided by
> > 'grub-probe' to search the encrypted partition first:
> >
> > search --fs-uuid --set=root --hint='cryptouuid/<PART-UUID>' <FS-UUID>
> >
> > However, for LVM on an encrypted partition, the search hint provided by
> > 'grub-probe' is:
> >
> >   --hint='lvmid/<VG-UUID>/<LV-UUID>'
> >
> > It doesn't guarantee to look up the logical volume from the encrypted
> > partition, so the attacker may have the chance to fool grub2 to boot
> > into the malicious disk.
> >
> > To minimize the attack surface, this commit tweaks the disk device search
> > in diskfilter to look up cryptodisk devices first and then others, so
> > that the auto-unlocked disk will be found first, not the attacker's disk.
> >
> > Cc: Fabian Vogt <fvogt@suse.com>
> > Signed-off-by: Gary Lin <glin@suse.com>
> > Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
> 
> Otherwise Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>...
> 
> Daniel