linux-kernel - Re: [PATCH] disable kaslr in kdump kernel

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Message-ID: <20140211131640.GB1055@redhat.com>
Date:	Tue, 11 Feb 2014 08:16:40 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Dave Young <dyoung@...hat.com>
Cc:	keescook@...omium.org, hpa@...or.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] disable kaslr in kdump kernel

On Tue, Feb 11, 2014 at 06:08:38PM +0800, Dave Young wrote:
> 
> KASLR does not work in kdump kernel because it's too early that mem=exactmap
> has not been parsed.
> 
> Since KASLR does not make much sense for kdump kernel thus let's disable it
> for kdump kernel. To check if it is a kdump kernel I just check the cmdline
> param elfcorehdr just like is_kdump_kernel.
> 
> Signed-off-by: Dave Young <dyoung@...hat.com>

I don't think it is a good idea. I don't like hardcoding second kernel's
behavior. I rather vary second kernel's behavior based on command line
parameters or based on values passed in bootparams.

So I am more than happy to pass command line option "nokaslr" instead
of hardcoding this in kernel.

Thanks
Vivek

> ---
>  linux-2.6/arch/x86/boot/compressed/aslr.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> Index: dyoung/git/linux-2.6/arch/x86/boot/compressed/aslr.c
> ===================================================================
> --- linux-2.6/arch/x86/boot/compressed/aslr.c
> +++ linux-2.6/arch/x86/boot/compressed/aslr.c
> @@ -293,6 +293,11 @@ unsigned char *choose_kernel_location(un
>  		goto out;
>  	}
>  
> +	if (cmdline_find_option("elfcorehdr", NULL, 0) != -1) {
> +		debug_putstr("KASLR disabled...\n");
> +		goto out;
> +	}
> +
>  	/* Record the various known unsafe memory ranges. */
>  	mem_avoid_init((unsigned long)input, input_size,
>  		       (unsigned long)output, output_size);
--
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