From: Bill Irwin <bill.irwin@oracle.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Bill Irwin <bill.irwin@oracle.com>,
Dan Kruchinin <dubalom@gmail.com>,
linux-kernel@vger.kernel.org,
Jeremy Fitzhardinge <jeremy@xensource.com>,
Andi Kleen <ak@suse.de>, Ingo Molnar <mingo@elte.hu>,
wli@holomorphy.com
Subject: Re: [RFC BUG?] dereference PAGE_OFFSET address (rc7-mm2)
Date: Wed, 2 May 2007 03:06:00 -0700 [thread overview]
Message-ID: <20070502100600.GZ26598@holomorphy.com> (raw)
In-Reply-To: <20070502084617.GY26598@holomorphy.com>
On Wed, May 02, 2007 at 12:51:40AM -0700, Andrew Morton wrote:
>> Thanks for the report. I can reproduce it.
>> Bisection shows that x86_64-mm-paravirt-initial-pagetable.patch caused
>> this.
>> I didn't check whether the patch actually permits us to read kernel
>> memory. Probably it does. Probably we'd prefer that it didn't ;)
On Wed, May 02, 2007 at 01:46:17AM -0700, Bill Irwin wrote:
> Brown paper bag time. I don't know how it got past me.
Brain dump before crashing for the night:
The patch refuses to clobber already-present pagetable entries of
whatever origin. There are pagetables prior to this setup covering the
address range just above PAGE_OFFSET. If this theory is correct, you
should only be able to go a few MB above PAGE_OFFSET before encountering
unreadable kernel memory. IIRC those pagetables are a statically
allocated array in assembly; altering that array to set supervisor bits
may resolve it, though it may also be freed as initmem.
-- wli
next prev parent reply other threads:[~2007-05-02 10:06 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-02 3:26 [RFC BUG?] dereference PAGE_OFFSET address (rc7-mm2) Dan Kruchinin
2007-05-02 7:51 ` Andrew Morton
2007-05-02 8:46 ` Bill Irwin
2007-05-02 10:06 ` Bill Irwin [this message]
2007-05-02 16:28 ` Jeremy Fitzhardinge
2007-05-02 16:32 ` Bill Irwin
2007-05-02 16:51 ` Andi Kleen
2007-05-02 17:16 ` Eric W. Biederman
2007-05-02 17:52 ` Bill Irwin
2007-05-02 19:13 ` Eric W. Biederman
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