From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 116C09000BD for ; Thu, 29 Sep 2011 13:29:22 -0400 (EDT) Received: by bkbzs2 with SMTP id zs2so1221715bkb.14 for ; Thu, 29 Sep 2011 10:29:20 -0700 (PDT) Date: Thu, 29 Sep 2011 21:28:21 +0400 From: Vasiliy Kulikov Subject: Re: [PATCH 2/2] mm: restrict access to /proc/meminfo Message-ID: <20110929172821.GA19601@albatros> References: <20110927175453.GA3393@albatros> <20110927175642.GA3432@albatros> <20110927193810.GA5416@albatros> <20110929161848.GA16348@albatros> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110929161848.GA16348@albatros> Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Christoph Lameter , kernel-hardening@lists.openwall.com, Pekka Enberg , Matt Mackall , Andrew Morton , linux-mm@kvack.org, Kees Cook , Dave Hansen , Valdis.Kletnieks@vt.edu, Linus Torvalds , Alan Cox , linux-kernel@vger.kernel.org On Thu, Sep 29, 2011 at 20:18 +0400, Vasiliy Kulikov wrote: > On Tue, Sep 27, 2011 at 13:33 -0700, David Rientjes wrote: > > I'd much rather just convert everything to use MB rather than KB so you > > can't determine things at a page level. I think that gets us much closer > > to what the patch is intending to restrict. But I also expect some > > breakage from things that just expect meminfo to be in KB units without > > parsing what the kernel is exporting. > > I'm not convinced with rounding the information to MBs. The attacker > still may fill slabs with new objects to trigger new slab pages > allocations. He will be able to see when this MB-granularity barrier is > overrun thus seeing how many kbs there were before: > > old = new - filled_obj_size_sum > > As `new' is just increased, it means it is known with KB granularity, > not MB. By counting used slab objects he learns filled_obj_size_sum. s/filled_obj_size_sum/old/ of course. > So, rounding gives us nothing, but obscurity. > > Thanks, -- Vasiliy Kulikov http://www.openwall.com - bringing security into open computing environments -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org