linux-kernel - Re: BUG: unable to handle kernel paging request at ffffc7ff81000398 (sys_kexec

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Message-ID: <1327763490.16907.1.camel@lappy>
Date:	Sat, 28 Jan 2012 10:11:30 -0500
From:	Sasha Levin <levinsasha928@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Dave Jones <davej@...hat.com>, kexec@...ts.infradead.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: BUG: unable to handle kernel paging request at ffffc7ff81000398
 (sys_kexec_load)

On Sat, 2012-01-21 at 20:49 -0800, Eric W. Biederman wrote:
> Interesting.
> 
> The fact that this happens in native_set_pte would suggest that we are
> trying to write to a page table that does not exist.  So this might
> be a layer below kexec_load that has the problem.
> 
> Do you have the kernel you were testing?    A disassembly of the
> native_set_pte, machine_kexec_prepare and sys_kexec_load
> would be interesting, for attempting to trace this back to what went
> wrong.

I did some work into investigating it today, looks like it's simple to trigger it using the following code:

	#include <fcntl.h>
	int main(void)
	{
		char dummy[4096] = {0};
		syscall(246, 0xffffffff81008000, 1, dummy, 2);
		return 0;
	}

I'll continue trying to figure out whats wrong, but hopefully this lead will help in reproducing it easily.

-- 

Sasha.

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