Date: Tue, 4 Jun 2019 11:31:26 +0530 From: Kaiwan N Billimoria <kaiwan@...wantech.com> To: Kees Cook <keescook@...omium.org> Cc: Alexander Potapenko <glider@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>, Dmitry Vyukov <dvyukov@...gle.com>, James Morris <jmorris@...ei.org>, Jann Horn <jannh@...gle.com>, Kostya Serebryany <kcc@...gle.com>, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, Masahiro Yamada <yamada.masahiro@...ionext.com>, Matthew Wilcox <willy@...radead.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Randy Dunlap <rdunlap@...radead.org>, Sandeep Patil <sspatil@...roid.com>, "Serge E. Hallyn" <serge@...lyn.com>, Souptick Joarder <jrdr.linux@...il.com>, Marco Elver <elver@...gle.com>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linux Memory Management List <linux-mm@...ck.org>, linux-security-module <linux-security-module@...r.kernel.org> Subject: Re: [PATCH v5 2/3] mm: init: report memory auto-initialization features at boot time On Tue, Jun 4, 2019 at 8:44 AM Kees Cook <keescook@...omium.org> wrote: > > On Mon, Jun 03, 2019 at 11:24:49AM +0200, Alexander Potapenko wrote: > > On Sat, Jun 1, 2019 at 3:18 AM Andrew Morton <akpm@...ux-foundation.org> wrote: > > > > > > On Wed, 29 May 2019 14:38:11 +0200 Alexander Potapenko <glider@...gle.com> wrote: > > > > > > > Print the currently enabled stack and heap initialization modes. > > > > > > > > The possible options for stack are: > > > > - "all" for CONFIG_INIT_STACK_ALL; > > > > - "byref_all" for CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL; > > > > - "byref" for CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF; > > > > - "__user" for CONFIG_GCC_PLUGIN_STRUCTLEAK_USER; > > > > - "off" otherwise. > > > > > > > > Depending on the values of init_on_alloc and init_on_free boottime > > > > options we also report "heap alloc" and "heap free" as "on"/"off". > > > > > > Why? > > > > > > Please fully describe the benefit to users so that others can judge the > > > desirability of the patch. And so they can review it effectively, etc. > > I'm going to update the description with the following passage: > > > > Print the currently enabled stack and heap initialization modes. > > > > Stack initialization is enabled by a config flag, while heap > > initialization is configured at boot time with defaults being set > > in the config. It's more convenient for the user to have all information > > about these hardening measures in one place. > > > > Does this make sense? > > > Always! > > > > > > > In the init_on_free mode initializing pages at boot time may take some > > > > time, so print a notice about that as well. > > > > > > How much time? > > I've seen pauses up to 1 second, not actually sure they're worth a > > separate line in the log. > > Kees, how long were the delays in your case? > > I didn't measure it, but I think it was something like 0.5 second per GB. > I noticed because normally boot flashes by. With init_on_free it pauses > for no apparent reason, which is why I suggested the note. (I mean *I* > knew why it was pausing, but it might surprise someone who sets > init_on_free=1 without really thinking about what's about to happen at > boot.) (Pardon the gmail client) How about: - if (want_init_on_free()) - pr_info("Clearing system memory may take some time...\n"); + if (want_init_on_free()) + pr_info("meminit: clearing system memory may take some time...\n"); or even + if (want_init_on_free()) + pr_info("meminit (init_on_free == 1): clearing system memory may take some time...\n"); or some combo thereof? -- Kaiwan > > -- > Kees Cook >
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