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

From: Marc Zyngier <maz@kernel.org>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: "Neal Liu" <neal.liu@mediatek.com>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Will Deacon" <will@kernel.org>, "Lars Persson" <lists@bofh.nu>,
	"Mark Rutland" <mark.rutland@arm.com>,
	DTML <devicetree@vger.kernel.org>,
	"Herbert Xu" <herbert@gondor.apana.org.au>,
	wsd_upstream <wsd_upstream@mediatek.com>,
	"Sean Wang" <sean.wang@kernel.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Crystal Guo (郭晶)" <Crystal.Guo@mediatek.com>,
	"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
	"Matt Mackall" <mpm@selenic.com>,
	"Matthias Brugger" <matthias.bgg@gmail.com>,
	"linux-mediatek@lists.infradead.org"
	<linux-mediatek@lists.infradead.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v5 3/3] hwrng: add mtk-sec-rng driver
Date: Mon, 2 Dec 2019 19:11:46 +0000	[thread overview]
Message-ID: <20191202191146.79e6368c@why> (raw)
In-Reply-To: <CAKv+Gu_um7eRYXbieW7ogDX5mmZaxP7JQBJM9CajK+6CsO5RgQ@mail.gmail.com>

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

> (adding some more arm64 folks)
> 
> On Fri, 29 Nov 2019 at 11:30, Neal Liu <neal.liu@mediatek.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@mediatek.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...