Re: [RFC PATCH v5 1/1] Add dm verity root hash pkcs7 sig validation.

[Jaskaran Singh Khurana]

Hello Eric/Milan,

On Fri, 28 Jun 2019, Milan Broz wrote:

> On 28/06/2019 05:00, Eric Biggers wrote:
> > > Hello Eric,
> > >
> > > This started with a config (see V4). We didnot want scripts that pass this
> > > parameter to suddenly stop working if for some reason the verification is
> > > turned off so the optional parameter was just parsed and no validation
> > > happened if the CONFIG was turned off. This was changed to a commandline
> > > parameter after feedback from the community, so I would prefer to keep it
> > > *now* as commandline parameter. Let me know if you are OK with this.
> > >
> > > Regards,
> > > JK
> >
> > Sorry, I haven't been following the whole discussion.  (BTW, you sent out
> > multiple versions both called "v4", and using a cover letter for a single patch
> > makes it unnecessarily difficult to review.)  However, it appears Milan were
> > complaining about the DM_VERITY_VERIFY_ROOTHASH_SIG_FORCE option which set the
> > policy for signature verification, *not* the DM_VERITY_VERIFY_ROOTHASH_SIG
> > option which enabled support for signature verification.  Am I missing
> > something?  You can have a module parameter which controls the "signatures
> > required" setting, while also allowing people to compile out kernel support for
> > the signature verification feature.
>
> Yes, this was exactly my point.
>
> I think I even mention in some reply to use exactly the same config Makefile logic
> as for FEC - to allow completely compile it out of the source:
>
> ifeq ($(CONFIG_DM_VERITY_FEC),y)
> dm-verity-objs                  += dm-verity-fec.o
> endif
>
> > Sure, it means that the signature verification support won't be guaranteed to be
> > present when dm-verity is.  But the same is true of the hash algorithm (e.g.
> > sha512), and of the forward error correction feature.  Since the signature
> > verification is nontrivial and pulls in a lot of other kernel code which might
> > not be otherwise needed (via SYSTEM_DATA_VERIFICATION), it seems a natural
> > candidate for putting the support behind a Kconfig option.
>
> On the other side, dm-verity is meant for a system verification, so if it depends
> on SYSTEM_DATA_VERIFICATION is ... not so surprising :)
>
> But the change above is quite easy and while we already have FEC as config option,
> perhaps let's do it the same here.
>
> Milan
Yes, I will make this change. Please consider this discussion as resolved. 
Thanks.

Regards,
Jaskaran.