Re: [tpmdd-devel] [PATCH] tpm: remove chip_num parameter from in-kernel API

[PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>]

On 24 October 2017 at 21:53, Jarkko Sakkinen
<jarkko.sakkinen@linux.intel.com> wrote:
> On Tue, Oct 24, 2017 at 09:21:15PM +0530, PrasannaKumar Muralidharan wrote:
>> On 24 October 2017 at 21:14, Jarkko Sakkinen
>> <jarkko.sakkinen@linux.intel.com> wrote:
>> > On Mon, Oct 23, 2017 at 10:31:39AM -0600, Jason Gunthorpe wrote:
>> >> On Mon, Oct 23, 2017 at 10:07:31AM -0400, Stefan Berger wrote:
>> >>
>> >> > >-int tpm_pcr_extend(u32 chip_num, int pcr_idx, const u8 *hash)
>> >> > >+int tpm_pcr_extend(int pcr_idx, const u8 *hash)
>> >> > >  {
>> >> >
>> >> >
>> >> > I think every kernel internal TPM driver API should be called with the
>> >> > tpm_chip as a parameter. This is in foresight of namespacing of IMA where we
>> >> > want to provide the flexibility of passing a dedicated vTPM to each
>> >> > namespace and IMA would use the chip as a parameter to all of these
>> >> > functions to talk to the right tpm_vtpm_proxy instance. From that
>> >> > perspective this patch goes into the wrong direction.
>> >>
>> >> Yes, we should ultimately try and get to there.. Someday the
>> >> tpm_chip_find_get() will need to become namespace aware.
>> >>
>> >> But this patch is along the right path, eliminating the chip_num is
>> >> the right thing to do..
>> >>
>> >> > >-  tpm2 = tpm_is_tpm2(TPM_ANY_NUM);
>> >> > >+  tpm2 = tpm_is_tpm2();
>> >> > >   if (tpm2 < 0)
>> >> > >           return tpm2;
>> >> > >
>> >> > >@@ -1008,7 +1007,7 @@ static int trusted_instantiate(struct key *key,
>> >> > >   switch (key_cmd) {
>> >> > >   case Opt_load:
>> >> > >           if (tpm2)
>> >> > >-                  ret = tpm_unseal_trusted(TPM_ANY_NUM, payload, options);
>> >> > >+                  ret = tpm_unseal_trusted(payload, options);
>> >>
>> >> Sequences like this are sketchy.
>> >>
>> >> It should be
>> >>
>> >> struct tpm_chip *tpm;
>> >>
>> >> tpm = tpm_chip_find_get()
>> >> tpm2 = tpm_is_tpm2(tpm);
>> >>
>> >> [..]
>> >>
>> >> if (tpm2)
>> >>      ret = tpm_unseal_trusted(tpm, payload, options);
>> >>
>> >> [..]
>> >>
>> >> tpm_put_chip(tpm);
>> >>
>> >> As hot plug could alter the 'tpm' between the two tpm calls.
>> >>
>> >> Jason
>> >
>> > This patch just removes bunch of dead code. It does not change existing
>> > semantics. What you are saying should be done after the dead code has
>> > been removed. This commit is first step to that direction.
>> >
>> > /Jarkko
>>
>> Please check the RFC [1]. It does use chip id. The rfc has issues and
>> has to be fixed but still there could be users of the API.
>>
>> 1. https://www.spinics.net/lists/linux-crypto/msg28282.html
>>
>> Regards,
>> PrasannaKumar
>
> 1. Every user in the kernel is using TPM_ANY_NUM, which means there are
>    no other users.

Completely agree that there is no in kernel users yet.

> 2. Moving struct tpm_rng to the TPM client is architecturally
>    uacceptable.

As there was no response to the patch there is no way to know whether
it is acceptable or not.

> 3. Using zero deos not give you any better guarantees on anything than
>    just using TPM_ANY_NUM.

Chip id is used, not zero.

> Why this patch is not CC'd to linux-integrity? It modifies the TPM
> driver. And in the worst way.

TPM list is moderated and the moderator has not approved it yet.
get_maintainer script did not say about linux-integrity mailing list.

It could be doing things in worst way but it is not known until some
one says. If no one tells it is the case I don't think it is possible
to fix. Which is what happened.

> Implementing the ideas that Jason explained is the senseful way to
> get stable access. modules.dep makes sure that the modules are loaded
> in the correct order.

If that is sensible then it is the way to go.

There must be a reason to believe what is sensible and what is not.
Looks like this RFC has helped in judging that.

Regards,
PrasannaKumar