Date: Thu, 11 Apr 2019 10:07:14 -0700 From: Kees Cook <keescook@...omium.org> To: Masahiro Yamada <yamada.masahiro@...ionext.com> Cc: Alexander Potapenko <glider@...gle.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>, Alexander Popov <alpopov@...ecurity.com>, Michal Marek <michal.lkml@...kovi.net>, Emese Revfy <re.emese@...il.com>, James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-security-module <linux-security-module@...r.kernel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH 3/3] kbuild: Implement Clang's stack initialization On Thu, Apr 11, 2019 at 1:06 AM Masahiro Yamada <yamada.masahiro@...ionext.com> wrote: > > On Thu, Apr 11, 2019 at 1:16 AM Kees Cook <keescook@...omium.org> wrote: > > > > CONFIG_INIT_STACK_ALL turns on stack initialization based on > > -ftrivial-auto-var-init in Clang builds and on > > -fplugin-arg-structleak_plugin-byref-all in GCC builds. > > Is CONFIG_INIT_STACK_ALL wired up to GCC plugin in any way? > I could not understand it from the code. No, it's only available under Clang. Clang is all-or-nothing, and the GCC plugin has a degrees up to "all passed by reference" which isn't truly "all" (i.e. Clang will initialize variables that aren't passed by reference and trigger a compiler warning about being uninitialized.) > > choice > > prompt "Initialize kernel stack variables at function entry" > > depends on CC_HAS_AUTO_VAR_INIT || GCC_PLUGINS > > + default INIT_STACK_ALL if CC_HAS_AUTO_VAR_INIT > > Why should this be enabled by default? > Ins't it a performance regression > since it inserts instructions in function prologue? There are very few users of Clang right now (mainly Android), so I figured it'd be nice to start Clang builds from a "protected by default" here, especially given Linus's thoughts on making this always happen. I don't want to do it for GCC yet, since that would likely come as a huge surprise to everyone else. :) But I'm happy to change this, of course. -Kees  https://lkml.kernel.org/r/CA+55aFykZL+cSBJjBBts7ebEFfyGPdMzTmLSxKnT_29=j942dA@mail.gmail.com -- Kees Cook
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