From: "H. Peter Anvin" <hpa@zytor.com>
To: Kees Cook <kees@outflux.net>
Cc: "Yan, Zheng" <zheng.z.yan@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: RW and executable hole in page tables on x86_64
Date: Fri, 25 Oct 2013 15:59:23 +0100 [thread overview]
Message-ID: <526A874B.2040108@zytor.com> (raw)
In-Reply-To: <20131025133454.GC4994@outflux.net>
On 10/25/2013 02:34 PM, Kees Cook wrote:
> Hi,
>
> I've noticed there's a chunk of kernel memory still marked RW and x. See
> 0xffffffff82956000 below...
>
> ---[ High Kernel Mapping ]---
> 0xffffffff80000000-0xffffffff81000000 16M pmd
> 0xffffffff81000000-0xffffffff81a00000 10M ro PSE GLB x pmd
> 0xffffffff81a00000-0xffffffff81e00000 4M ro PSE GLB NX pmd
> 0xffffffff81e00000-0xffffffff82200000 4M RW GLB NX pte
> 0xffffffff82200000-0xffffffff82800000 6M RW PSE GLB NX pmd
> 0xffffffff82800000-0xffffffff82956000 1368K RW GLB NX pte
> 0xffffffff82956000-0xffffffff82a00000 680K RW GLB x pte
> 0xffffffff82a00000-0xffffffffa0000000 470M pmd
>
> HPA looked at it for a bit, but it wasn't obvious what was going on. It's
> after the end of bss. I do note that the two adjacent regions add up to
> 2MiB. Is this some kind of leftover mapping? What is this region? Is there
> a sensible place to clean it up?
>
It looks to be what is left after the 2 MB page for bss is broken up.
It doesn't mean it isn't broken, though.
-hpa
next prev parent reply other threads:[~2013-10-25 14:59 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-25 13:34 RW and executable hole in page tables on x86_64 Kees Cook
2013-10-25 14:59 ` H. Peter Anvin [this message]
2014-11-14 19:02 ` Kees Cook
2014-11-14 20:04 ` Thomas Gleixner
2014-11-14 20:15 ` Kees Cook
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