linux-kernel - Re: [PATCH v5 3/3] hwrng: add mtk-sec-rng driver

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Date:   Mon, 2 Dec 2019 19:11:46 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Neal Liu <neal.liu@...iatek.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Lars Persson <lists@...h.nu>,
        Mark Rutland <mark.rutland@....com>,
        DTML <devicetree@...r.kernel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        Sean Wang <sean.wang@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Crystal Guo (郭晶)" 
        <Crystal.Guo@...iatek.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        Matt Mackall <mpm@...enic.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 3/3] hwrng: add mtk-sec-rng driver

On Mon, 2 Dec 2019 16:12:09 +0000
Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:

> (adding some more arm64 folks)
> 
> On Fri, 29 Nov 2019 at 11:30, Neal Liu <neal.liu@...iatek.com> wrote:
> >
> > On Fri, 2019-11-29 at 18:02 +0800, Lars Persson wrote:  
> > > Hi Neal,
> > >
> > > On Wed, Nov 27, 2019 at 3:23 PM Neal Liu <neal.liu@...iatek.com> wrote:  
> > > >
> > > > For MediaTek SoCs on ARMv8 with TrustZone enabled, peripherals like
> > > > entropy sources is not accessible from normal world (linux) and
> > > > rather accessible from secure world (ATF/TEE) only. This driver aims
> > > > to provide a generic interface to ATF rng service.
> > > >  
> > >
> > > I am working on several SoCs that also will need this kind of driver
> > > to get entropy from Arm trusted firmware.
> > > If you intend to make this a generic interface, please clean up the
> > > references to MediaTek and give it a more generic name. For example
> > > "Arm Trusted Firmware random number driver".
> > >
> > > It will also be helpful if the SMC call number is configurable.
> > >
> > > - Lars  
> >
> > Yes, I'm trying to make this to a generic interface. I'll try to make
> > HW/platform related dependency to be configurable and let it more
> > generic.
> > Thanks for your suggestion.
> >  
> 
> I don't think it makes sense for each arm64 platform to expose an
> entropy source via SMC calls in a slightly different way, and model it
> as a h/w driver. Instead, we should try to standardize this, and
> perhaps expose it via the architectural helpers that already exist
> (get_random_seed_long() and friends), so they get plugged into the
> kernel random pool driver directly.

Absolutely. I'd love to see a standard, ARM-specified, virtualizable
RNG that is abstracted from the HW.

> Note that in addition to drivers based on vendor SMC calls, we already
> have a RNG h/w driver based on OP-TEE as well, where the driver
> attaches to a standardized trusted OS interface identified by a UUID,
> and which also gets invoked via SMC calls into secure firmware.

... and probably an unhealthy number of hypervisor-specific hacks that
do the same thing. The sooner we plug this, the better.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...