|| ||Peter Zijlstra <peterz-AT-infradead.org> |
|| ||"Larry H." <research-AT-subreption.com> |
|| ||Re: [patch 0/5] Support for sanitization flag in low-level page
|| ||Sat, 30 May 2009 12:39:33 +0200|
|| ||Arjan van de Ven <arjan-AT-infradead.org>, Alan Cox <alan-AT-lxorguk.ukuu.org.uk>, Ingo Molnar <mingo-AT-elte.hu>, Rik van Riel <riel-AT-redhat.com>, linux-kernel-AT-vger.kernel.org, Linus Torvalds <torvalds-AT-osdl.org>, linux-mm-AT-kvack.org, Ingo Molnar <mingo-AT-redhat.com>, pageexec-AT-freemail.hu|
|| ||Article, Thread
On Fri, 2009-05-29 at 22:48 -0700, Larry H. wrote:
> On 07:32 Fri 29 May , Arjan van de Ven wrote:
> > On Thu, 28 May 2009 21:36:01 +0200
> > Peter Zijlstra <email@example.com> wrote:
> > > > ... and if we zero on free, we don't need to zero on allocate.
> > > > While this is a little controversial, it does mean that at least
> > > > part of the cost is just time-shifted, which means it'll not be TOO
> > > > bad hopefully...
> > >
> > > zero on allocate has the advantage of cache hotness, we're going to
> > > use the memory, why else allocate it.
> Because zero on allocate kills the very purpose of this patch and it has
> obvious security implications. Like races (in information leak
> scenarios, that is). What happens in-between the release of the page and
> the new allocation that yields the same page? What happens if no further
> allocations happen in a while (that can return the old page again)?
> That's the idea.
I don't get it, these are in-kernel data leaks, you need to be able to
run kernel code to exploit these, if someone can run kernel code, you've
Why waste time on this?
> > So if you zero on free, the next allocation will reuse the zeroed page.
> > And due to LIFO that is not too far out "often", which makes it likely
> > the page is still in L2 cache.
> Thanks for pointing this out clearly, Arjan.
Thing is, the time between allocation and use is typically orders of
magnitude less than between free and use.
Really, get a life, go fix real bugs. Don't make our kernel slower for
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