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

[Sumit Garg]

Thanks Mimi for your comments.

On Wed, 21 Oct 2020 at 08:51, Mimi Zohar <zohar@xxxxxxxxxxxxx> 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)").

> 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.

>
> trusted_key_ops should be defined as __ro_after_init, like is currently
> done for other LSM structures.

Sure, will do.

>
> > +
> > +     /*
> > +      * 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.

-Sumit

>
> thanks,
>
> Mimi
>