Date: Fri, 17 May 2019 14:59:16 +0200 From: Michal Hocko <mhocko@...nel.org> To: Alexander Potapenko <glider@...gle.com> Cc: akpm@...ux-foundation.org, cl@...ux.com, keescook@...omium.org, 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>, Souptick Joarder <jrdr.linux@...il.com>, Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org, linux-security-module@...r.kernel.org Subject: Re: [PATCH v2 3/4] gfp: mm: introduce __GFP_NO_AUTOINIT [It would be great to keep people involved in the previous version in the CC list] On Tue 14-05-19 16:35:36, Alexander Potapenko wrote: > When passed to an allocator (either pagealloc or SL[AOU]B), > __GFP_NO_AUTOINIT tells it to not initialize the requested memory if the > init_on_alloc boot option is enabled. This can be useful in the cases > newly allocated memory is going to be initialized by the caller right > away. > > __GFP_NO_AUTOINIT doesn't affect init_on_free behavior, except for SLOB, > where init_on_free implies init_on_alloc. > > __GFP_NO_AUTOINIT basically defeats the hardening against information > leaks provided by init_on_alloc, so one should use it with caution. > > This patch also adds __GFP_NO_AUTOINIT to alloc_pages() calls in SL[AOU]B. > Doing so is safe, because the heap allocators initialize the pages they > receive before passing memory to the callers. I still do not like the idea of a new gfp flag as explained in the previous email. People will simply use it incorectly or arbitrarily. We have that juicy experience from the past. Freeing a memory is an opt-in feature and the slab allocator can already tell many (with constructor or GFP_ZERO) do not need it. So can we go without this gfp thing and see whether somebody actually finds a performance problem with the feature enabled and think about what can we do about it rather than add this maint. nightmare from the very beginning? -- Michal Hocko SUSE Labs
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