linux-kernel - Re: arch_align_stack() seems useless

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Message-ID: <46D42057.9090507@gmail.com>
Date:	Tue, 28 Aug 2007 15:17:11 +0200
From:	Franck Bui-Huu <vagabon.xyz@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: arch_align_stack() seems useless

Hello Arjan,

Arjan van de Ven wrote:
> arch_align_stack aligns, on x86, within a 2 page range (this is for
> cache coloring).

OK, but for elf case this seems useless since the top of the stack is
already randomized.

It seems that the randomization stuff (top of the stack + stack
pointer inside a page) belongs to the elf binary format whereas it
could have been part of exec.c. Are there any reasons ?

> The other thing you missed is that arch_align_stack()
> is called in 2 locations, binfmt_elf.c is the primary location for
> inside-the-page randomization.
> 

Well not really because for mips case, we have:

	$ git grep ELF_PLATFORM include/asm-mips
	include/asm-mips/elf.h:#define ELF_PLATFORM  (NULL)

So on mips, the stack pointer won't get the inside the page
randomization. Is that correct ?

If so, I'm wondering why this randomization must depend on that string
to be defined. I must admit that I'm not sure how it's used. I guess
it's used by ld.so and it could be set to "mips" for now...

thanks
		Franck
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