Date: Wed, 28 Feb 2018 10:33:49 -0800 From: Matthew Wilcox <willy@...radead.org> To: Ilya Smith <blackzert@...il.com> Cc: Kees Cook <keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org>, Dan Williams <dan.j.williams@...el.com>, Michal Hocko <mhocko@...e.com>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Jan Kara <jack@...e.cz>, Jerome Glisse <jglisse@...hat.com>, Hugh Dickins <hughd@...gle.com>, Helge Deller <deller@....de>, Andrea Arcangeli <aarcange@...hat.com>, Oleg Nesterov <oleg@...hat.com>, Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: [RFC PATCH] Randomization of address chosen by mmap. On Wed, Feb 28, 2018 at 08:13:00PM +0300, Ilya Smith wrote: > > It would be worth spelling out the "not recommended" bit some more > > too: this fragments the mmap space, which has some serious issues on > > smaller address spaces if you get into a situation where you cannot > > allocate a hole large enough between the other allocations. > > > > I’m agree, that's the point. Would it be worth randomising the address returned just ever so slightly? ie instead of allocating exactly the next address, put in a guard hole of (configurable, by default maybe) 1-15 pages? Is that enough extra entropy to foil an interesting number of attacks, or do we need the full randomise-the-address-space approach in order to be useful?
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