From mboxrd@z Thu Jan  1 00:00:00 1970
From: mark.rutland@arm.com (Mark Rutland)
Date: Tue, 30 Aug 2016 11:24:39 +0100
Subject: [PATCH v2 4/9] arm64: head.S: move KASLR processing out of
 __enable_mmu()
In-Reply-To: <CAKv+Gu-N+-Qykg30UDaisgA+J1e0p-+GGuE9diz1=Hoh_yPPtw@mail.gmail.com>
References: <1472049366-10922-1-git-send-email-ard.biesheuvel@linaro.org>
 <1472049366-10922-5-git-send-email-ard.biesheuvel@linaro.org>
 <20160824203609.GA1642@remoulade> <20160824204654.GA1775@remoulade>
 <CAKv+Gu-N+-Qykg30UDaisgA+J1e0p-+GGuE9diz1=Hoh_yPPtw@mail.gmail.com>
Message-ID: <20160830102439.GC1223@leverpostej>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, Aug 25, 2016 at 02:59:51PM +0100, Ard Biesheuvel wrote:
> On 24 August 2016 at 21:46, Mark Rutland <mark.rutland@arm.com> wrote:
> > On Wed, Aug 24, 2016 at 09:36:10PM +0100, Mark Rutland wrote:
> >> On Wed, Aug 24, 2016 at 04:36:01PM +0200, Ard Biesheuvel wrote:
> >> > +__primary_switch:
> >> > +#ifdef CONFIG_RANDOMIZE_BASE
> >> > +   mov     x19, x0                         // preserve new SCTLR_EL1 value
> >> > +   mrs     x20, sctlr_el1                  // preserve old SCTLR_EL1 value
> >> > +#endif
> >> > +
> >> > +   adr     x27, 0f
> >> > +   b       __enable_mmu
> >>
> >> As we do elsewhere, it's probably worth a comment on the line with the ADR into
> >> x27, mentioning that __enable_mmu will branch there.
> >>
> >> ... or perhaps we should just have __enable_mmu return to the LR like a normal
> >> AAPCS function, place the switch routines in the idmap, and use the idiomatic
> >> sequence:
> >>
> >> __thing_switch:
> >>       bl      __enable_mmu
> >>       ldr     xN, =__thing
> >>       blr     xN
> >
> > ... and now I see that this is what subsequent patches do ;)
> >
> > Is it possible to first AAPCS-ify __enable_mmu (with shuffling of callers as
> > above) in one patch, prior to this?
> 
> Yes, but that would result in an __enable_mmu() that needs to stash
> the link register value, and essentially returns twice in the KASLR
> case.

Ah, good point. I had missed that.

> As an intermediate step working towards the result after the series, I
> think the adr + label above is the lesser evil

Yes, it probably is.

I'll try to flip back into review mode, keeping the above in mind.

Thanks,
Mark.