Re: [PATCH v7 1/4] KEYS: trusted: Add generic trusted keys framework

[Sumit Garg <sumit.garg@linaro.org>]

On Wed, 21 Oct 2020 at 17:55, Mimi Zohar <zohar@linux.ibm.com> wrote:
>
> On Wed, 2020-10-21 at 11:16 +0530, Sumit Garg wrote:
> > Thanks Mimi for your comments.
> >
> > On Wed, 21 Oct 2020 at 08:51, Mimi Zohar <zohar@linux.ibm.com> wrote:
> > >
> > > On Wed, 2020-10-07 at 15:37 +0530, Sumit Garg wrote:
> > >
> > > > +/*
> > > > + * trusted_destroy - clear and free the key's payload
> > > > + */
> > > > +static void trusted_destroy(struct key *key)
> > > > +{
> > > > +     kfree_sensitive(key->payload.data[0]);
> > > > +}
> > > > +
> > > > +struct key_type key_type_trusted = {
> > > > +     .name = "trusted",
> > > > +     .instantiate = trusted_instantiate,
> > > > +     .update = trusted_update,
> > > > +     .destroy = trusted_destroy,
> > > > +     .describe = user_describe,
> > > > +     .read = trusted_read,
> > > > +};
> > > > +EXPORT_SYMBOL_GPL(key_type_trusted);
> > > > +
> > > > +static int __init init_trusted(void)
> > > > +{
> > > > +     int i, ret = 0;
> > > > +
> > > > +     for (i = 0; i < ARRAY_SIZE(trusted_key_sources); i++) {
> > > > +             if (trusted_key_source &&
> > > > +                 strncmp(trusted_key_source, trusted_key_sources[i].name,
> > > > +                         strlen(trusted_key_sources[i].name)))
> > > > +                     continue;
> > > > +
> > > > +             trusted_key_ops = trusted_key_sources[i].ops;
> > > > +
> > > > +             ret = trusted_key_ops->init();
> > > > +             if (!ret)
> > > > +                     break;
> > > > +     }
> > >
> > > In the case when the module paramater isn't specified and both TPM and
> > > TEE are enabled, trusted_key_ops is set to the last source initialized.
> >
> > I guess there is some misunderstanding. Here it's only a single trust
> > source (TPM *or* TEE) is initialized and only that trust source would
> > be active at runtime. And trusted_key_ops would be initialized to the
> > first trust source whose initialization is successful (see check: "if
> > (!ret)").
>
> My mistake.
>
> >
> > > After patch 2/4, the last trusted source initialized is TEE.  If the
> > > intention is to limit it to either TPM or TEE, then trusted_key_ops
> > > should have a default value, which could be overwritten at runtime.
> > > That would address Luke Hind's concerns of making the decision at
> > > compile time.
> >
> > I think traversing the trust source list with the initial value being
> > TPM would be default value.
>
> Agreed
> >
> > >
> > > trusted_key_ops should be defined as __ro_after_init, like is currently
> > > done for other LSM structures.
> >
> > Sure, will do.
>
> Thanks
> >
> > >
> > > > +
> > > > +     /*
> > > > +      * encrypted_keys.ko depends on successful load of this module even if
> > > > +      * trusted key implementation is not found.
> > > > +      */
> > > > +     if (ret == -ENODEV)
> > > > +             return 0;
> > > > +
> > > > +     return ret;
> > > > +}
> > > > +
> > > > +static void __exit cleanup_trusted(void)
> > > > +{
> > > > +     trusted_key_ops->exit();
> > >
> > > If the intention is really to support both TPM and TEE trusted keys at
> > > the same time, as James suggested, then the same "for" loop as in
> > > init_trusted() is needed here and probably elsewhere.
> >
> > Current intention is to only support a single trust source (TPM or
> > TEE) at runtime. But in future if there are use-cases then framework
> > can be extended to support multiple trust sources at runtime as well.
>
> Ok, the last sentence of the patch description, "Also, add a module
> parameter in order to select a particular trust source in case a
> platform support multiple trust sources.", needs to be expanded to:
> - indicate only one trust source at a time is supported
> - indicate the default, if the module_param is not specified
>

Sure, I will expand that.

> I would also change the word from "add" to "define".

Ack.

>   The new "source"
> module parameter needs to be added to the admin-guide/kernel-parameters
> documentation.

Okay, will update documentation as well.

-Sumit

>
> thanks,
>
> Mimi
>
>