Commit 42eaa27d authored by Alexander Potapenko's avatar Alexander Potapenko Committed by Andrew Morton
Browse files

security: kmsan: fix interoperability with auto-initialization 

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.

Link: https://lkml.kernel.org/r/20220915150417.722975-31-glider@google.com


Signed-off-by: default avatarAlexander Potapenko <glider@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 74d89909

mm/page_alloc.c

+4 −0
Original line number Diff line number Diff line
@@ -938,6 +938,10 @@ 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;

security/Kconfig.hardening

+4 −0
Original line number Diff line number Diff line
@@ -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

		help

		  Initializes everything on the stack (including padding)

		  with a zero value. This is intended to eliminate all
@@ -218,6 +220,7 @@ config STACKLEAK_RUNTIME_DISABLE 


config INIT_ON_ALLOC_DEFAULT_ON

	bool "Enable heap memory zeroing on allocation by default"

	depends on !KMSAN

	help

	  This has the effect of setting "init_on_alloc=1" on the kernel

	  command line. This can be disabled with "init_on_alloc=0".
@@ -230,6 +233,7 @@ config INIT_ON_ALLOC_DEFAULT_ON 


config INIT_ON_FREE_DEFAULT_ON

	bool "Enable heap memory zeroing on free by default"

	depends on !KMSAN

	help

	  This has the effect of setting "init_on_free=1" on the kernel

	  command line. This can be disabled with "init_on_free=0".