linux-kernel - Re: [Problem] kernel hangs at boot (bisected 892d208bcf)

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Date:	Thu, 19 Jan 2012 14:00:58 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Dirk Gouders <gouders@...bocholt.fh-gelsenkirchen.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Problem] kernel hangs at boot (bisected 892d208bcf)

On Thu, Jan 19, 2012 at 12:16:56PM +0000, Dirk Gouders wrote:
> Catalin Marinas <catalin.marinas@....com> writes:
> > On Wed, Jan 18, 2012 at 07:32:59PM +0000, Dirk Gouders wrote:
> >> Freeing unused kernel memory: 608k freed
> >> kernel tried to execute NX-protected page - exploit attempt? (uid: 0)
> >> BUG: unable to handle kernel paging request at ffffffff818b232b
> >> IP: [<ffffffff818b232b>] kmemleak_late_init+0x8a/0x8a
...
> >> Code: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc <cc> cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
> >> RIP  [<ffffffff818b232b>] kmemleak_late_init+0x8a/0x8a
> >
> > I don't really see how kmemleak could cause such error (or any of the
> > recent changes I have made). It looks like some of the code in the
> > .init.text section is not executable.

Ah, the interesting part - 0xcc is the poison value for freed initmem.
And from the kernel logs you posted Linux frees the initmem and later
calls kmemleak_late_init() which should have been in the .init.text
section.

The kmemleak_late_init() function is defined as:

static int __init kmemleak_late_init(void)
{
...
}
late_initcall(kmemleak_late_init);

and it must *not* be called after the initmem has been freed. Was there
any change in the x86 or generic code with regards to the freeing of the
init memory?

-- 
Catalin
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