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

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Message-ID: <CAFA6WYMvqmCVjjb9vW0y+_2+AtoGUE0ZvwBhc4F=4Es-94redA@mail.gmail.com>
Date:   Wed, 14 Oct 2020 10:34:38 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Janne Karhunen <janne.karhunen@...il.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Markus Wamser <Markus.Wamser@...ed-mode.de>,
        Luke Hinds <lhinds@...hat.com>,
        "open list:ASYMMETRIC KEYS" <keyrings@...r.kernel.org>,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        op-tee@...ts.trustedfirmware.org,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v7 1/4] KEYS: trusted: Add generic trusted keys framework

On Tue, 13 Oct 2020 at 17:29, Jarkko Sakkinen
<jarkko.sakkinen@...ux.intel.com> wrote:
>
> On Tue, Oct 13, 2020 at 04:23:36PM +0530, Sumit Garg wrote:
> > On Tue, 13 Oct 2020 at 07:13, Jarkko Sakkinen
> > <jarkko.sakkinen@...ux.intel.com> wrote:
> > >
> > > On Wed, Oct 07, 2020 at 03:37:45PM +0530, Sumit Garg wrote:
> > > > Current trusted keys framework is tightly coupled to use TPM device as
> > > > an underlying implementation which makes it difficult for implementations
> > > > like Trusted Execution Environment (TEE) etc. to provide trusted keys
> > > > support in case platform doesn't posses a TPM device.
> > > >
> > > > Add a generic trusted keys framework where underlying implementations
> > > > can be easily plugged in. Create struct trusted_key_ops to achieve this,
> > > > which contains necessary functions of a backend.
> > > >
> > > > Also, add a module parameter in order to select a particular trust source
> > > > in case a platform support multiple trust sources.
> > > >
> > > > Suggested-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > > > Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
> > >
> > > This is exactly kind of place where I think static_call() should be
> > > taken into use, which is a v5.10 feature [1]. For background and
> > > context, I'd read [2].
> >
> > This looks like an interesting feature. But I am not sure about the
> > real benefits that it will provide in case of trusted keys. If we are
> > looking at it performance wise then I think the gain will be
> > negligible when compared with slow TPM communication interface (eg.
> > SPI, I2C) or when compared with context switching involved in TEE.
> >
> > Also, it requires arch specific support too which currently seems to
> > be limited to x86 only.
>
> Please, do not purposely add indirect calls, unless you  must. Here it's
> not a must.
>
> static_call() is the correct kernel idiom to define what you are doing
> in this patch. arch's will catch up.

Okay, fair enough. I will try to use it instead.

>
> > > The other thing that I see that does not make much else than additional
> > > complexity, is trusted_tpm.ko. We can do with one trusted.ko.
> > >
> >
> > Current implementation only builds a single trusted.ko module. There
> > isn't any trusted_tpm.ko.
> > -Sumit
>
> You're right, I'm sorry. I misread this:
>
> -static void __exit cleanup_trusted(void)
> +static void __exit exit_tpm_trusted(void)
>  {
>         if (chip) {
>                 put_device(&chip->dev);
> @@ -1257,7 +1029,11 @@  static void __exit cleanup_trusted(void)
>         }
>  }
>
> -late_initcall(init_trusted);
> -module_exit(cleanup_trusted);
> -
> -MODULE_LICENSE("GPL");
> +struct trusted_key_ops tpm_trusted_key_ops = {
> +       .migratable = 1, /* migratable by default */
> +       .init = init_tpm_trusted,
> +       .seal = tpm_trusted_seal,
> +       .unseal = tpm_trusted_unseal,
> +       .get_random = tpm_trusted_get_random,
> +       .exit = exit_tpm_trusted,
> +};
>
> Please remove "__init" and  "__exit" for the functions as they are used
> as fields as members of a struct that has neither life span. That messed
> up my head.

Okay.

>
> Please use a single convention for the function names. It would
> be optimal to prefix with the subsystem name because that makes easier
> to use tracing tools:  trusted_tpm_<callback name> would work.
>

Okay.

-Sumit

> /Jarkko