linux-kernel - Re: Executability of the stack

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Date:	Thu, 14 Dec 2006 10:57:24 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	Franck Pommereau <pommereau@...v-paris12.fr>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Executability of the stack

On Thu, 2006-12-14 at 10:26 +0100, Franck Pommereau wrote:
> Dear Linux developers,
> 
> I recently discovered that the Linux kernel on 32 bits x86 processors
> reports the stack as being non-executable while it is actually
> executable (because located in the same memory segment).

this is not per se true, it depends on the capabilities of your 32 bit
x86 processor.

> # grep maps /proc/self/maps
> bfce8000-bfcfe000 rw-p bfce8000 00:00 0          [stack]

this shows that the *intent* is to have it non-executable. 
Not all x86 processors can enforce this. All modern ones do.

> Is there any reason for this situation? 

the alternative (showing effective permission) is equally confusing;
apps would see permissions they didn't set...

> Maybe it comes from sharing source code for 64 bits and 32 bits
> architectures but if so, it should be possible (and highly desirable) to
> treat 32 bits differently.

it's not a "32 bit" thing, it's an "older processors don't, newer ones
do" thing.

Can you paste your /proc/cpuinfo file here ? Maybe you have a processor
with the capability but just haven't enabled it (either in the bios or
in the kernel config)

Greetings,
   Arjan van de Ven

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