linux-kernel - Re: access

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Message-Id: <200907141843.05629.arnd@arndb.de>
Date:	Tue, 14 Jul 2009 18:43:05 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	monstr@...str.eu
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	LTP <ltp-list@...ts.sourceforge.net>
Subject: Re: access_ok macor

On Tuesday 14 July 2009, Michal Simek wrote:
> Arnd Bergmann wrote:

> >>  r29=00000000, r30=00000000, r31=CE9759A4, rPC=C000123C
> >>  msr=800045AE, ear=00000001, esr=000000B2, fsr=000080D0
> >> Segmentation fault
> >>
> > 
> > I guess then you should check if 0xc000123c is in your
> > exception table, or why it is not.
> 
> on that address is load instruction for unaligned exception because addr is odd number
> that's why is called unaligned exception handler and from this function
> is called load instruction which failed. :-(
> 
> Currently this make more sense why that tests failed. If that pointers are
> even number exception is not taken and exception sure don't have fixup for it because
> this is generic code. :-(
> 
> That's the problem because we are looking for regs->pc but this point to unaligned exception
> handler.

Ok, that makes a lot of sense.

The solution then is to handle fixups from the unaligned exception handler
if you come from the kernel. That should fix the three text cases.

I don't fully understand your exception handling there, but I think you
also need to add code checking for __range_ok() to your unaligned handler,
to prevent malicious user space code from accessing the kernel through
unaligned pointers.

	Arnd <><
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