Date: Thu, 29 Sep 2011 21:28:21 +0400 From: Vasiliy Kulikov <segoon@...nwall.com> To: David Rientjes <rientjes@...gle.com> Cc: Christoph Lameter <cl@...two.org>, kernel-hardening@...ts.openwall.com, Pekka Enberg <penberg@...nel.org>, Matt Mackall <mpm@...enic.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, Kees Cook <kees@...ntu.com>, Dave Hansen <dave@...ux.vnet.ibm.com>, Valdis.Kletnieks@...edu, Linus Torvalds <torvalds@...ux-foundation.org>, Alan Cox <alan@...ux.intel.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/2] mm: restrict access to /proc/meminfo 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
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