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

From: Will Deacon <will@kernel.org>
To: Marc Zyngier <maz@kernel.org>
Cc: "Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
	"Neal Liu" <neal.liu@mediatek.com>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"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: Tue, 3 Dec 2019 10:17:20 +0000	[thread overview]
Message-ID: <20191203101720.GD6815@willie-the-truck> (raw)
In-Reply-To: <20191202191146.79e6368c@why>

On Mon, Dec 02, 2019 at 07:11:46PM +0000, Marc Zyngier wrote:
> 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.

Same here. I hacked up some initial code for doing this with KVM [1], but
I'd much rather it was part of a standard service specification so that
we could use the same interface for talking to the firmware and the
hypervisor.

Will

[1] https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/log/?h=kvm/hvc