linux-kernel - Re: brk randomization breaks columns

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Date:	Tue, 5 Feb 2008 19:24:46 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, Pavel Machek <pavel@....cz>,
	Hugh Dickins <hugh@...itas.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	Abel Bernabeu <abel.bernabeu@...il.com>
Subject: Re: brk randomization breaks columns

On Tue, 5 Feb 2008 23:35:27 +0100 (CET) Jiri Kosina wrote:

> On Tue, 5 Feb 2008, Arjan van de Ven wrote:
> 
> > the combo of a config option + sysctl sounds the right way forward then 
> > ;(
> 
> OK, so I propose the one below (unested yet, but should be trivial). Does 
> anyone have any objections?
> 
> 
> 
> From: Jiri Kosina <jkosina@...e.cz>
> 
> ASLR: add possibility for more fine-grained tweaking
> 
> Some prehistoric binaries don't like when start of brk area is located 
> anywhere else than just after code+bss.
> 
> This patch adds possibility to configure the default behavior of address 
> space randomization. In addition to that, randomize_va_space now can have 
> value of '2', which means full randomization including brk space.
> 
> Also, documentation of randomize_va_space is added.

Thanks.

> Signed-off-by: Jiri Kosina <jkosina@...e.cz>
> 
> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
> index 8984a53..0373bbe 100644
> --- a/Documentation/sysctl/kernel.txt
> +++ b/Documentation/sysctl/kernel.txt
> @@ -41,6 +41,7 @@ show up in /proc/sys/kernel:
>  - pid_max
>  - powersave-nap               [ PPC only ]
>  - printk
> +- randomize_va_space
>  - real-root-dev               ==> Documentation/initrd.txt
>  - reboot-cmd                  [ SPARC only ]
>  - rtsig-max
> @@ -280,6 +281,37 @@ send before ratelimiting kicks in.
>  
>  ==============================================================
>  
> +randomize-va-space:
> +
> +This option can be used to select the type of process address
> +space randomization is used in the system, for architectures

s/is used/that is used/

> +that support this feature.
> +
> +One of the following numeric values is possible:
> +
> +0 - [none]
> +	Turn the process address space randomization off by default.
> +
> +1 - [conservative]
> +	Conservative address space randomization makes the addresses of
> +	mmap base and VDSO page randomized. This, among other things,
> +	implies that shared libraries will be loaded to random addresses.
> +	Also for PIE binaries, the location of code start is randomized.
> +
> +2 - [full]
> +
> +	This includes all the features that Conservative randomization
> +	provides. In addition to that, also start of the brk area is
> +	randomized.
> +	There a few legacy applications out there (such as some ancient
> +	versions of libc.so.5 from 1996), that assume that brk area starts

                    Drop comma          ^             that the brk area

> +	just after the end of the code+bss. These applications break when
> +	start of the brk area is randomized. There are however no known
> +	non-legacy applications that would be broken this way, so for most
> +	systems it is safe to chose Full randomization.

                              choose

> +
> +==============================================================
> +
>  reboot-cmd: (Sparc only)
>  
>  ??? This seems to be a way to give an argument to the Sparc

> diff --git a/init/Kconfig b/init/Kconfig
> index 87f50df..804a3a6 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -662,6 +662,46 @@ config SLOB
>  
>  endchoice
>  
> +choice
> +	prompt "Address space randomization type"
> +	default RANDOMIZATION_CONSERVATIVE
> +	help
> +	   This option allows to select the type of process address space
> +	   randomization that will be used by default (for those architectures
> +	   that support address space randomization). This option can be
> +	   overriden in runtime through kernel.randomize_va_space sysctl.
> +
> +config RANDOMIZATION_NONE
> +	bool "NONE"
> +	help
> +	   Turn the process address space randomization off by default.
> +	   Equivalent to sysctl kernel.randomize_va_space = 0.
> +
> +config RANDOMIZATION_CONSERVATIVE
> +	bool "CONSERVATIVE"
> +	help
> +	   Conservative address space randomization makes the addresses of
> +	   mmap base and VDSO page randomized. This, among other things,
> +	   implies that shared libraries will be loaded to random addresses.
> +	   Also for PIE binaries, the location of code start is randomized.
> +	   Equivalent to sysctl kernel.randomize_va_space = 1.
> +
> +config RANDOMIZATION_FULL
> +	bool "FULL"
> +	help
> +	   This includes all the features that Conservative randomization
> +	   provides. In addition to that, also start of the brk area is
> +	   randomized.
> +	   There a few legacy applications out there (such as some ancient
> +	   versions of libc.so.5 from 1996), that assume that brk area starts

Drop comma.  s/that brk/that the brk/

> +	   just after the end of the code+bss. These applications break when
> +	   start of the brk area is randomized. There are however no known
> +	   non-legacy applications that would be broken this way, so for most
> +	   systems it is safe to chose Full randomization.

s/chose/choose/

> +	   Equivalent to sysctl kernel.randomize_va_space = 2.
> +
> +endchoice
> +
>  config PROFILING
>  	bool "Profiling support (EXPERIMENTAL)"
>  	help

---
~Randy
--
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