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Message-ID: <20160810101253.GL1041@n2100.armlinux.org.uk>
Date: Wed, 10 Aug 2016 11:12:53 +0100
From: Russell King - ARM Linux <linux@...linux.org.uk>
To: Arnd Bergmann <arnd@...db.de>
Cc: linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
Kees Cook <keescook@...omium.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, x86@...nel.org,
linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
Andrew Morton <akpm@...ux-foundation.org>,
Mathias Krause <minipli@...glemail.com>
Subject: Re: [PATCH 2/2] arm: apply more __ro_after_init
On Wed, Aug 10, 2016 at 12:00:53PM +0200, Arnd Bergmann wrote:
> On Wednesday, August 10, 2016 10:43:39 AM CEST Russell King - ARM Linux wrote:
> > On Fri, Jun 03, 2016 at 11:40:24AM -0700, Kees Cook wrote:
> > > @@ -1309,16 +1309,11 @@ void __init arm_mm_memblock_reserve(void)
> > > * Any other function or debugging method which may touch any device _will_
> > > * crash the kernel.
> > > */
> > > +static char vectors[PAGE_SIZE * 2] __ro_after_init __aligned(PAGE_SIZE);
> > > static void __init devicemaps_init(const struct machine_desc *mdesc)
> > > {
> > > struct map_desc map;
> > > unsigned long addr;
> > > - void *vectors;
> > > -
> > > - /*
> > > - * Allocate the vector page early.
> > > - */
> > > - vectors = early_alloc(PAGE_SIZE * 2);
> >
> > This one is not appropriate. We _do_ write to these pages after init
> > for FIQ handler updates. See set_fiq_handler().
>
> Is that the only thing that modifies the page? If we think this is a
> valuable change, we could make it depend on the absence of FIQ
> support, as very few platforms (rpc, omap1, s3c24xx and possibly
> imx) seem to even use it.
There's the TLS emulation too, but that writes via the vectors mapping
at 0xffff0ff0.
--
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