linux-kernel - Re: [PATCH] dt-bindings: mailbox: arm,mhu: Make secure interrupt optional

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Date:   Fri, 29 Jul 2022 10:18:04 -0500
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: mailbox: arm,mhu: Make secure interrupt optional

On Fri, Jul 29, 2022 at 6:10 AM Sudeep Holla <sudeep.holla@....com> wrote:
> On Thu, Jul 28, 2022 at 04:07:45PM -0500, Jassi Brar wrote:

> > >
> > I could learn why specifying secure irq isn't desirable?
> > No non-secure client node would ask for that secure irq/channel, which
> > will simply lay unused.
>
> Did you mean would or wouldn't ?
>
I mean what's written.

> Anyways I can insert a module that requests this channel and bring down
> the system as accessing anything configure secure from non-secure side
> on Juno results in system hang/error.
>
Why go to those lengths? These are already simpler options available  ;-)
1)   while (1) ;      // preferably in some atomic context
2)   *((int *) 0) = 0;   // you might want to iterate over offset for
guaranteed results
3) Slightly more work, but you also have the opportunity to erase your
storage device


> > index f6c55877fbd94..004b1566be74d 100644
> > --- a/arch/arm64/boot/dts/arm/juno-base.dtsi
> > +++ b/arch/arm64/boot/dts/arm/juno-base.dtsi
> > @@ -26,7 +26,8 @@ mailbox: mhu@...f0000 {
> >         compatible = "arm,mhu", "arm,primecell";
> >         reg = <0x0 0x2b1f0000 0x0 0x1000>;
> >         interrupts = <GIC_SPI 36 IRQ_TYPE_LEVEL_HIGH>,
> > -                <GIC_SPI 35 IRQ_TYPE_LEVEL_HIGH>;
> > +                <GIC_SPI 35 IRQ_TYPE_LEVEL_HIGH>,
> > +                <GIC_SPI 37 IRQ_TYPE_LEVEL_HIGH>;
> >         interrupt-names = "mhu_lpri_rx",
> >                   "mhu_hpri_rx";
> >         #mbox-cells = <1>;
> >
> > If this works for you, I could submit a proper patch.
>
> No this doesn't work IMO.
>
If you _really_ tested and faced an error, please share it.

> Yes standalone everything looks fine, but you can
> insert a module requesting this channel and bring down the system.
>
If anyone other than a super-user is able to do that, then you have a
serious security problem at hand.
If you do that as a super-user, have fun.

cheers.