From: linux@arm.linux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v6 7/8] ARM: mm: allow non-text sections to be non-executable
Date: Fri, 26 Sep 2014 17:59:13 +0100 [thread overview]
Message-ID: <20140926165913.GX5182@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <CAGXu5jL+ksQ4nq4pxOk7gM0POmwtTQ7DgmugpVK45arpMLGzvg@mail.gmail.com>
On Fri, Sep 26, 2014 at 09:43:12AM -0700, Kees Cook wrote:
> On Fri, Sep 26, 2014 at 4:42 AM, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
> > On Thu, Sep 18, 2014 at 12:19:08PM -0700, Kees Cook wrote:
> >> @@ -1373,13 +1373,24 @@ static void __init map_lowmem(void)
> >> if (start >= end)
> >> break;
> >>
> >> - if (end < kernel_x_start || start >= kernel_x_end) {
> >> + if (end < kernel_x_start) {
> >> map.pfn = __phys_to_pfn(start);
> >> map.virtual = __phys_to_virt(start);
> >> map.length = end - start;
> >> map.type = MT_MEMORY_RWX;
> >>
> >> create_mapping(&map);
> >> + } else if (start >= kernel_x_end) {
> >> + map.pfn = __phys_to_pfn(start);
> >> + map.virtual = __phys_to_virt(start);
> >> + map.length = end - start;
> >> +#ifdef CONFIG_ARM_KERNMEM_PERMS
> >> + map.type = MT_MEMORY_RW;
> >> +#else
> >> + map.type = MT_MEMORY_RWX;
> >> +#endif
> >> +
> >> + create_mapping(&map);
> >
> >
> > I'm looking at this, and wondering two things. Firstly, why isn't it
> > MT_MEMORY_RW in the first place. Secondly, why do you need to make
> > this depend on CONFIG_ARM_KERNMEM_PERMS at all?
> >
> > I think the first is an oversight by me (and is a case which never came
> > up in my testing, because most of my platforms don't have segmented
> > memory layouts.)
> >
> > The second I think is not necessary - the memory region being considered
> > is not part of the kernel at all, and so should not be executable in any
> > shape or form.
>
> I'm happy to change this. My original intent was to make layout for
> builds without CONFIG_ARM_KERNMEM_PERMS identical to what was there
> before, so I took this step to make sure.
>
> I will drop the #ifdef and respin. Does the rest look ok? Shall I send
> a pull request?
I think all you need to is change that MT_MEMORY_RWX to be MT_MEMORY_RW.
However, I think I would also like to see the kernel text being read-only
as soon as possible - so maybe we should also have MT_MEMORY_RX, and
have map_lowmem() use this for the kernel text when we want this level
of protection?
--
FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up
according to speedtest.net.
next prev parent reply other threads:[~2014-09-26 16:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-18 19:19 [PATCH v6 0/8] arm: support CONFIG_RODATA Kees Cook
2014-09-18 19:19 ` [PATCH v6 1/8] arm: use generic fixmap.h Kees Cook
2014-09-18 19:19 ` [PATCH v6 2/8] ARM: expand fixmap region to 3MB Kees Cook
2014-09-18 19:19 ` [PATCH v6 3/8] arm: fixmap: implement __set_fixmap() Kees Cook
2014-09-18 19:19 ` [PATCH v6 4/8] arm: use fixmap for text patching when text is RO Kees Cook
2014-09-18 19:19 ` [PATCH v6 5/8] ARM: kexec: Make .text R/W in machine_kexec Kees Cook
2014-09-18 19:19 ` [PATCH v6 6/8] arm: kgdb: Handle read-only text / modules Kees Cook
2014-09-18 19:19 ` [PATCH v6 7/8] ARM: mm: allow non-text sections to be non-executable Kees Cook
2014-09-26 11:42 ` Russell King - ARM Linux
2014-09-26 16:43 ` Kees Cook
2014-09-26 16:59 ` Russell King - ARM Linux [this message]
2014-09-26 17:07 ` Kees Cook
2014-09-18 19:19 ` [PATCH v6 8/8] ARM: mm: allow text and rodata sections to be read-only Kees Cook
2014-09-26 5:58 ` [PATCH v6 0/8] arm: support CONFIG_RODATA Kees Cook
2014-09-26 11:21 ` Will Deacon
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