linux-kernel - Re: [GIT PULL] x86/kaslr for v3.14

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Message-ID: <CAGXu5jKTr1udKiD7mhVEkN2W4z0w687DS=jJMORTT+ny+DqGCg@mail.gmail.com>
Date:	Fri, 7 Feb 2014 11:44:47 -0800
From:	Kees Cook <keescook@...omium.org>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Cong Ding <dinggnu@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mathias Krause <minipli@...glemail.com>,
	Michael Davidson <md@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Wei Yongjun <yongjun_wei@...ndmicro.com.cn>,
	Dave Young <dyoung@...hat.com>,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [GIT PULL] x86/kaslr for v3.14

On Fri, Feb 7, 2014 at 11:07 AM, H. Peter Anvin <hpa@...ux.intel.com> wrote:
> On 02/07/2014 06:49 AM, Vivek Goyal wrote:
>>
>> As a workaround, Dave is currently using "nokaslr" command line parameter
>> for second kernel. He is still facing issues where makedumpfile segment
>> faults. He is looking into it further.
>>
>
> Now, let's state this: kaslr for kdump is almost certainly useless (the
> amount of reserved memory is not enough to provide any meaningful
> randomization, so any randomization needs to happen during the memory
> reservation phase.)  So disabling kaslr in the kdump kernel is entirely
> appropriate.

Peter covered everything already, but yeah, kaslr and kdump may not
make a lot of sense together, but regardless, yes, it only examines
e820 for memory space. It has to do all this work before the kernel
decompresses, so it's very early.

-Kees

-- 
Kees Cook
Chrome OS Security
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