From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 7 Jun 2019 08:34:54 -0700 From: Kees Cook Subject: Re: [PATCH v6 2/3] mm: init: report memory auto-initialization features at boot time Message-ID: <201906070822.CEF77C844E@keescook> References: <20190606164845.179427-1-glider@google.com> <20190606164845.179427-3-glider@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190606164845.179427-3-glider@google.com> To: Alexander Potapenko Cc: Andrew Morton , Christoph Lameter , Dmitry Vyukov , James Morris , Jann Horn , Kostya Serebryany , Laura Abbott , Mark Rutland , Masahiro Yamada , Matthew Wilcox , Nick Desaulniers , Randy Dunlap , Sandeep Patil , "Serge E. Hallyn" , Souptick Joarder , Marco Elver , Kaiwan N Billimoria , kernel-hardening@lists.openwall.com, linux-mm@kvack.org, linux-security-module@vger.kernel.org List-ID: On Thu, Jun 06, 2019 at 06:48:44PM +0200, Alexander Potapenko wrote: > 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. Perhaps for clarity, add this to the end of the sentence: "... at boot, so the user can reason about the expected behavior of the running system." > 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". > > In the init_on_free mode initializing pages at boot time may take some > time, so print a notice about that as well. Perhaps give an example too: This depends on how much memory is installed, the memory bandwidth, etc. On a relatively modern x86 system, it takes about 0.75s/GB to wipe all memory: [ 0.418722] mem auto-init: stack:byref_all, heap alloc:off, heap free:on [ 0.419765] mem auto-init: clearing system memory may take some time... [ 12.376605] Memory: 16408564K/16776672K available (14339K kernel code, 1397K rwdata, 3756K rodata, 1636K init, 11460K bss, 368108K reserved, 0K cma-reserved) More notes below... > > Signed-off-by: Alexander Potapenko > Suggested-by: Kees Cook > To: Andrew Morton > To: Christoph Lameter > Cc: Dmitry Vyukov > Cc: James Morris > Cc: Jann Horn > Cc: Kostya Serebryany > Cc: Laura Abbott > Cc: Mark Rutland > Cc: Masahiro Yamada > Cc: Matthew Wilcox > Cc: Nick Desaulniers > Cc: Randy Dunlap > Cc: Sandeep Patil > Cc: "Serge E. Hallyn" > Cc: Souptick Joarder > Cc: Marco Elver > Cc: Kaiwan N Billimoria > Cc: kernel-hardening@lists.openwall.com > Cc: linux-mm@kvack.org > Cc: linux-security-module@vger.kernel.org > --- > v6: > - update patch description, fixed message about clearing memory > --- > init/main.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) > > diff --git a/init/main.c b/init/main.c > index 66a196c5e4c3..e68ef1f181f9 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -520,6 +520,29 @@ static inline void initcall_debug_enable(void) > } > #endif > > +/* Report memory auto-initialization states for this boot. */ > +void __init report_meminit(void) Sorry I missed this before: it should be a static function. > +{ > + const char *stack; > + > + if (IS_ENABLED(CONFIG_INIT_STACK_ALL)) > + stack = "all"; > + else if (IS_ENABLED(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL)) > + stack = "byref_all"; > + else if (IS_ENABLED(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF)) > + stack = "byref"; > + else if (IS_ENABLED(CONFIG_GCC_PLUGIN_STRUCTLEAK_USER)) > + stack = "__user"; > + else > + stack = "off"; > + > + pr_info("mem auto-init: stack:%s, heap alloc:%s, heap free:%s\n", > + stack, want_init_on_alloc(GFP_KERNEL) ? "on" : "off", > + want_init_on_free() ? "on" : "off"); > + if (want_init_on_free()) > + pr_info("mem auto-init: clearing system memory may take some time...\n"); > +} > + > /* > * Set up kernel memory allocators > */ > @@ -530,6 +553,7 @@ static void __init mm_init(void) > * bigger than MAX_ORDER unless SPARSEMEM. > */ > page_ext_init_flatmem(); > + report_meminit(); > mem_init(); > kmem_cache_init(); > pgtable_init(); > -- > 2.22.0.rc1.311.g5d7573a151-goog > But other than that: Acked-by: Kees Cook -- Kees Cook