On Tue, Dec 14, 2021 at 05:20:48PM +0100, Alexander Potapenko wrote: > Heap and stack initialization is great, but not when we are trying > uses of uninitialized memory. When the kernel is built with KMSAN, > having kernel memory initialization enabled may introduce false > negatives. > > We disable CONFIG_INIT_STACK_ALL_PATTERN and CONFIG_INIT_STACK_ALL_ZERO > under CONFIG_KMSAN, making it impossible to auto-initialize stack > variables in KMSAN builds. We also disable CONFIG_INIT_ON_ALLOC_DEFAULT_ON > and CONFIG_INIT_ON_FREE_DEFAULT_ON to prevent accidental use of heap > auto-initialization. > > We however still let the users enable heap auto-initialization at > boot-time (by setting init_on_alloc=1 or init_on_free=1), in which case > a warning is printed. > > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> > --- > Link: https://linux-review.googlesource.com/id/I86608dd867018683a14ae1870f1928ad925f42e9 > --- > mm/page_alloc.c | 4 ++++ > security/Kconfig.hardening | 4 ++++ > 2 files changed, 8 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index fa8029b714a81..4218dea0c76a2 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -855,6 +855,10 @@ void init_mem_debugging_and_hardening(void) > else > static_branch_disable(&init_on_free); > > + if (IS_ENABLED(CONFIG_KMSAN) && > + (_init_on_alloc_enabled_early || _init_on_free_enabled_early)) > + pr_info("mem auto-init: please make sure init_on_alloc and init_on_free are disabled when running KMSAN\n"); > + > #ifdef CONFIG_DEBUG_PAGEALLOC > if (!debug_pagealloc_enabled()) > return; > diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening > index d051f8ceefddd..bd13a46024457 100644 > --- a/security/Kconfig.hardening > +++ b/security/Kconfig.hardening > @@ -106,6 +106,7 @@ choice > config INIT_STACK_ALL_PATTERN > bool "pattern-init everything (strongest)" > depends on CC_HAS_AUTO_VAR_INIT_PATTERN > + depends on !KMSAN > help > Initializes everything on the stack (including padding) > with a specific debug value. This is intended to eliminate > @@ -124,6 +125,7 @@ choice > config INIT_STACK_ALL_ZERO > bool "zero-init everything (strongest and safest)" > depends on CC_HAS_AUTO_VAR_INIT_ZERO > + depends on !KMSAN So this means KMSAN is a developer debugging feature only and should never be turned on on a real device/server that has users? thanks, greg k-h
