linux-kernel - Re: [RFC] ARM: omap3: Enable HWMODS for HW Random Number Generator

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Date:   Tue, 10 Sep 2019 16:44:52 +0200
From:   Pali Rohár <pali.rohar@...il.com>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     Adam Ford <aford173@...il.com>, Tony Lindgren <tony@...mide.com>,
        Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Paul Walmsley <paul@...an.com>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Russell King <linux@...linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tero Kristo <t-kristo@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Benoît Cousson <bcousson@...libre.com>,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        Adam Ford <adam.ford@...icpd.com>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC] ARM: omap3: Enable HWMODS for HW Random Number Generator

On Tuesday 10 September 2019 15:37:32 Sebastian Reichel wrote:
> Hi,
> 
> On Tue, Sep 10, 2019 at 08:56:49AM -0500, Adam Ford wrote:
> > On Thu, Sep 5, 2019 at 6:04 PM Tony Lindgren <tony@...mide.com> wrote:
> > > Oh and this needs to default to status = "disabled" for
> > > HS devices like n900 as it needs to use the omap3-rom-rng.
> > 
> > I don't know enough about the HS version of the OMAP3, but what's the
> > main difference between omap3-rom-rng and this one?
> 
> The OMAP HS chips have the bus firewall configured to block direct
> access to some cryptography related devices. The kernel will crash
> with a bus error, if you try to read/write the registers for
> protected devices.

And if you try to read it more times, SOC would be rebooted for security
reasons.

> The omap3-rom-rng avoids this by communicating
> with the security middleware component instead of directly accessing
> the RNG hardware.

And that component is loaded by signed bootloader into "secure" area not
accessible by "non-secure" work (like kernel) and communication is done
via arm smc instruction.

-- 
Pali Rohár
pali.rohar@...il.com