Date: Tue, 23 Apr 2019 10:31:48 +0200 From: Michal Hocko <mhocko@...nel.org> To: Dave Hansen <dave.hansen@...el.com> Cc: Alexander Potapenko <glider@...gle.com>, akpm@...ux-foundation.org, cl@...ux.com, dvyukov@...gle.com, keescook@...omium.org, labbott@...hat.com, linux-mm@...ck.org, linux-security-module@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH 1/3] mm: security: introduce the init_allocations=1 boot option On Thu 18-04-19 09:35:32, Dave Hansen wrote: > On 4/18/19 8:42 AM, Alexander Potapenko wrote: > > This option adds the possibility to initialize newly allocated pages and > > heap objects with zeroes. This is needed to prevent possible information > > leaks and make the control-flow bugs that depend on uninitialized values > > more deterministic. > > Isn't it better to do this at free time rather than allocation time? If > doing it at free, you can't even have information leaks for pages that > are in the allocator. I would tend to agree here. Free path is usually less performance sensitive than the allocation. Those really hot paths tend to defer the work. I am also worried that an opt-out gfp flag would tend to be used incorrectly as the history has shown for others - e.g. __GFP_TEMPORARY. So I would rather see this robust without a fine tuning unless there is real use case that would suffer from this and we can think of a background scrubbing or something similar. -- Michal Hocko SUSE Labs
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