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Date: Wed, 10 Aug 2016 13:06:34 -0400
From: Daniel Micay <danielmicay@...il.com>
To: kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org>
Cc: linux-arch@...r.kernel.org, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
x86@...nel.org, linux-kernel@...r.kernel.org, Andrew Morton
<akpm@...ux-foundation.org>, Mathias Krause <minipli@...glemail.com>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: Re: [PATCH 2/2] arm: apply more
__ro_after_init
On Wed, 2016-08-10 at 10:43 +0100, 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().
This is one of the many cases where pax_open_kernel/pax_close_kernel are
needed to temporarily toggle it read-only. From grsecurity:
@@ -95,7 +95,10 @@ void set_fiq_handler(void *start, unsigned int
length)
void *base = vectors_page;
unsigned offset = FIQ_OFFSET;
+ pax_open_kernel();
memcpy(base + offset, start, length);
+ pax_close_kernel();
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