On Thu, Apr 11, 2019 at 1:06 AM Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote: > > On Thu, Apr 11, 2019 at 1:16 AM Kees Cook <keescook@xxxxxxxxxxxx> 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[1]. 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 [1] https://lkml.kernel.org/r/CA+55aFykZL+cSBJjBBts7ebEFfyGPdMzTmLSxKnT_29=j942dA@xxxxxxxxxxxxxx -- Kees Cook
