Date: Fri, 17 May 2019 16:20:48 +0200 From: Michal Hocko <mhocko@...nel.org> To: Alexander Potapenko <glider@...gle.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>, Kees Cook <keescook@...omium.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Masahiro Yamada <yamada.masahiro@...ionext.com>, James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, Nick Desaulniers <ndesaulniers@...gle.com>, Kostya Serebryany <kcc@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Sandeep Patil <sspatil@...roid.com>, Laura Abbott <labbott@...hat.com>, Randy Dunlap <rdunlap@...radead.org>, Jann Horn <jannh@...gle.com>, Mark Rutland <mark.rutland@....com>, Linux Memory Management List <linux-mm@...ck.org>, linux-security-module <linux-security-module@...r.kernel.org> Subject: Re: [PATCH v2 1/4] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options On Fri 17-05-19 16:11:32, Alexander Potapenko wrote: > On Fri, May 17, 2019 at 4:04 PM Michal Hocko <mhocko@...nel.org> wrote: > > > > On Tue 14-05-19 16:35:34, Alexander Potapenko wrote: > > > The new options are needed to prevent possible information leaks and > > > make control-flow bugs that depend on uninitialized values more > > > deterministic. > > > > > > init_on_alloc=1 makes the kernel initialize newly allocated pages and heap > > > objects with zeroes. Initialization is done at allocation time at the > > > places where checks for __GFP_ZERO are performed. > > > > > > init_on_free=1 makes the kernel initialize freed pages and heap objects > > > with zeroes upon their deletion. This helps to ensure sensitive data > > > doesn't leak via use-after-free accesses. > > > > Why do we need both? The later is more robust because even free memory > > cannot be sniffed and the overhead might be shifted from the allocation > > context (e.g. to RCU) but why cannot we stick to a single model? > init_on_free appears to be slower because of cache effects. It's > several % in the best case vs. <1% for init_on_alloc. This doesn't really explain why we need both. -- Michal Hocko SUSE Labs
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