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Re: [RFC] User stack pointer randomisation

To: Franck Bui-Huu <vagabon.xyz@gmail.com>
Subject: Re: [RFC] User stack pointer randomisation
From: Ralf Baechle <ralf@linux-mips.org>
Date: Thu, 19 Jul 2007 12:14:40 +0100
Cc: linux-mips <linux-mips@linux-mips.org>
In-reply-to: <469F0E5F.4050005@innova-card.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <469F0E5F.4050005@innova-card.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.14 (2007-02-12)
On Thu, Jul 19, 2007 at 09:10:23AM +0200, Franck Bui-Huu wrote:

> This patch adds a page size range randomisation to the user
> stack pointer.

Looks fine to me aside of the issue Nigel raised.

There is a constant defining the ABI-specific alignment in <asm/asm.h>:

#if (_MIPS_SIM == _MIPS_SIM_ABI32)
#define ALSZ    7
#define ALMASK  ~7
#endif
#if (_MIPS_SIM == _MIPS_SIM_NABI32) || (_MIPS_SIM == _MIPS_SIM_ABI64)
#define ALSZ    15
#define ALMASK  ~15
#endif

This will unnecessarily increase the alignment of the stack wasting a few
bytes of memory for O32 binaries running on 64-bit kernels but I'd just
ignore this artefact; the cure would be uglier than the disease ;-)

  Ralf

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