linux-kernel - Re: [PATCH 3/6] x86: kaslr: return location from decompress

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Message-ID: <517AF5F2.50404@zytor.com>
Date:	Fri, 26 Apr 2013 14:47:30 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Kees Cook <keescook@...omium.org>
CC:	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
	Matthew Garrett <mjg@...hat.com>,
	Matt Fleming <matt.fleming@...el.com>,
	Eric Northup <digitaleric@...gle.com>,
	Dan Rosenberg <drosenberg@...curity.com>,
	Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 3/6] x86: kaslr: return location from decompress_kernel

On 04/26/2013 12:03 PM, Kees Cook wrote:
> This allows decompress_kernel to return a new location for the kernel to
> be relocated to. With CONFIG_RANDOMIZE_BASE, the choose_kernel_location
> routine will select a new location to decompress the kernel, and is
> presently a no-op. The logic for bypassing this routine with "noaslr"
> on the kernel command line is handled.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  Documentation/kernel-parameters.txt |    4 ++++
>  arch/x86/boot/compressed/Makefile   |    2 +-
>  arch/x86/boot/compressed/aslr.c     |   21 +++++++++++++++++++++
>  arch/x86/boot/compressed/cmdline.c  |    2 +-
>  arch/x86/boot/compressed/head_32.S  |    2 +-
>  arch/x86/boot/compressed/head_64.S  |    2 +-
>  arch/x86/boot/compressed/misc.c     |    7 +++++--
>  arch/x86/boot/compressed/misc.h     |   22 ++++++++++++++++------
>  8 files changed, 50 insertions(+), 12 deletions(-)
>  create mode 100644 arch/x86/boot/compressed/aslr.c
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 8ccbf27..eb1c62c 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1862,6 +1862,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  	noapic		[SMP,APIC] Tells the kernel to not make use of any
>  			IOAPICs that may be present in the system.
>  
> +	noaslr		[X86]
> +			Disable kernel base offset ASLR (Address Space
> +			Layout Randomization) if built into the kernel.
> +
>  	noautogroup	Disable scheduler automatic task group creation.
>  
>  	nobats		[PPC] Do not use BATs for mapping kernel lowmem

Calling it "nokaslr" might be useful to note that it is specifically
about the kernel.

	-hpa


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