[PATCH v6 31/44] security: kmsan: fix interoperability with auto-initialization

Alexander Potapenko
2022-09-05T12:30:36Z

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@google.com>
---
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 b28093e3bb42a..e5eed276ee41d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -936,6 +936,10 @@ 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 bd2aabb2c60f9..2739a6776454e 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
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".
--
2.37.2.789.g6183377224-goog