linux-kernel - Re: Security Random Number Generator support

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Message-ID: <CAMj1kXHjAdk5=-uSh_=S9j5cz42zr3h6t+YYGy+obevuQDp0fg@mail.gmail.com>
Date:   Tue, 2 Jun 2020 14:14:33 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Neal Liu <neal.liu@...iatek.com>
Cc:     Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Sean Wang <sean.wang@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.infradead.org,
        lkml <linux-kernel@...r.kernel.org>, wsd_upstream@...iatek.com,
        Crystal Guo <Crystal.Guo@...iatek.com>
Subject: Re: Security Random Number Generator support

On Tue, 2 Jun 2020 at 10:15, Neal Liu <neal.liu@...iatek.com> wrote:
>
> These patch series introduce a security random number generator
> which provides a generic interface to get hardware rnd from Secure
> state. The Secure state can be Arm Trusted Firmware(ATF), Trusted
> Execution Environment(TEE), or even EL2 hypervisor.
>
> Patch #1..2 adds sec-rng kernel driver for Trustzone based SoCs.
> For security awareness SoCs on ARMv8 with TrustZone enabled,
> peripherals like entropy sources is not accessible from normal world
> (linux) and rather accessible from secure world (HYP/ATF/TEE) only.
> This driver aims to provide a generic interface to Arm Trusted
> Firmware or Hypervisor rng service.
>
>
> changes since v1:
> - rename mt67xx-rng to mtk-sec-rng since all MediaTek ARMv8 SoCs can reuse
>   this driver.
>   - refine coding style and unnecessary check.
>
>   changes since v2:
>   - remove unused comments.
>   - remove redundant variable.
>
>   changes since v3:
>   - add dt-bindings for MediaTek rng with TrustZone enabled.
>   - revise HWRNG SMC call fid.
>
>   changes since v4:
>   - move bindings to the arm/firmware directory.
>   - revise driver init flow to check more property.
>
>   changes since v5:
>   - refactor to more generic security rng driver which
>     is not platform specific.
>
> *** BLURB HERE ***
>
> Neal Liu (2):
>   dt-bindings: rng: add bindings for sec-rng
>   hwrng: add sec-rng driver
>

There is no reason to model a SMC call as a driver, and represent it
via a DT node like this.

It would be much better if this SMC interface is made truly generic,
and wired into the arch_get_random() interface, which can be used much
earlier.


>  .../devicetree/bindings/rng/sec-rng.yaml      |  53 ++++++
>  drivers/char/hw_random/Kconfig                |  13 ++
>  drivers/char/hw_random/Makefile               |   1 +
>  drivers/char/hw_random/sec-rng.c              | 155 ++++++++++++++++++
>  4 files changed, 222 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/rng/sec-rng.yaml
>  create mode 100644 drivers/char/hw_random/sec-rng.c
>
> --
> 2.18.0