linux-kernel - Re: kaslr relocation incompitable with kernel loaded high

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Date:	Mon, 21 Apr 2014 10:56:02 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	WANG Chao <chaowang@...hat.com>
Cc:	Kees Cook <keescook@...omium.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: kaslr relocation incompitable with kernel loaded high

On Mon, Apr 21, 2014 at 3:52 AM, WANG Chao <chaowang@...hat.com> wrote:
> Hi, Kees
>
> When I'm testing kaslr with kdump, I find that when 2nd kernel is loaded
> high, it doesn't boot.
>
> I reserved 128M memory at high with kernel cmdline
> "crashkernel=128M,high crashkernel=0,low", and for which I got:
>
> [    0.000000] Reserving 128MB of memory at 6896MB for crashkernel (System RAM: 6013MB)
>
> Then I load kdump kernel into the reserved memory region, using a local
> modified kexec-tools which is passing e820 in boot_params.
>
> The e820 map of system RAM passed to 2nd kernel:
>
> E820 memmap (of RAM):
> 0000000000001000-000000000009e3ff (1)
> 00000001af000000-00000001b6f5dfff (1)
> 00000001b6fff400-00000001b6ffffff (1)
>
> In which, 2nd kernel is loaded at 0x1b5000000.
>
> After triggerred a system crash, 2nd kernel doesn't boot even with
> "nokaslr" cmdline:
>
> # echo c > /proc/sysrq-trigger
> [..]
>
> I'm in purgatory
> early console in decompress_kernel
> KASLR disabled...
>
> Decompressing Linux... Parsing ELF... Performing relocations...
>
> 32-bit relocation outside of kernel!

Interesting, when kernel get at "early console in decompress_kernel"
kernel already in 64 bit...

what does it mean "32-bit relocation outside of kernel" ?

why 32-bit is involved ?

Yinghai
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