UserMode Linux needs deferred KASAN initialization as it has a custom
kasan_arch_is_ready() implementation that tracks shadow memory readiness
via the kasan_um_is_ready flag.
As it's explained in commit 5b301409e8bc("UML: add support for KASAN
under x86_64"), if CONFIG_STATIC_LINK=y, then it works only with
CONFIG_KASAN_OUTLINE instrumentation.
Calling kasan_init_generic() in the end of kasan_init() like in other
arch does not work for UML as kasan_init() is called way before
main()->linux_main(). It produces the SEGFAULT in:
kasan_init()
kasan_init_generic
kasan_enable
static_key_enable
STATIC_KEY_CHECK_USE
...
<kasan_init+173> movabs r9, kasan_flag_enabled
<kasan_init+183> movabs r8, __func__.2
<kasan_init+193> movabs rcx, 0x60a04540
<kasan_init+203> movabs rdi, 0x60a045a0
<kasan_init+213> movabs r10, warn_slowpath_fmt
WARN_ON_ONCE("static key '%pS' used before call to jump_label_init()")
<kasan_init+226> movabs r12, kasan_flag_enabled
That's why we need to call kasan_init_generic() which enables the
static flag after jump_label_init(). The earliest available place
is arch_mm_preinit().
kasan_init()
main()
start_kernel
setup_arch
jump_label_init
...
mm_core_init
arch_mm_preinit
kasan_init_generic()
PowerPC, for example, has kasan_late_init() in arch_mm_preinit().
Though there is no static key enabling there, but it should be the best
place to enable KASAN "fully".
Verified with defconfig, enabling KASAN.
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049
Signed-off-by: Sabyrzhan Tasbolatov <snovit...@gmail.com>
---
Changes in v4:
- Addressed the issue in UML arch, where kasan_init_generic() is
called before jump_label_init() (Andrey Ryabinin)
---
arch/um/Kconfig | 1 +
arch/um/include/asm/kasan.h | 5 -----
arch/um/kernel/mem.c | 12 +++++++++---
3 files changed, 10 insertions(+), 8 deletions(-)
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 9083bfdb773..8d14c8fc2cd 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -5,6 +5,7 @@ menu "UML-specific options"
config UML
bool
default y
+ select ARCH_DEFER_KASAN
select ARCH_WANTS_DYNAMIC_TASK_STRUCT
select ARCH_HAS_CACHE_LINE_SIZE
select ARCH_HAS_CPU_FINALIZE_INIT
diff --git a/arch/um/include/asm/kasan.h b/arch/um/include/asm/kasan.h
index f97bb1f7b85..81bcdc0f962 100644
--- a/arch/um/include/asm/kasan.h
+++ b/arch/um/include/asm/kasan.h
@@ -24,11 +24,6 @@
#ifdef CONFIG_KASAN
void kasan_init(void);
-extern int kasan_um_is_ready;
-
-#ifdef CONFIG_STATIC_LINK
-#define kasan_arch_is_ready() (kasan_um_is_ready)
-#endif
#else
static inline void kasan_init(void) { }
#endif /* CONFIG_KASAN */
diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
index 76bec7de81b..704a26211ed 100644
--- a/arch/um/kernel/mem.c
+++ b/arch/um/kernel/mem.c
@@ -21,10 +21,10 @@
#include <os.h>
#include <um_malloc.h>
#include <linux/sched/task.h>
+#include <linux/kasan.h>
#ifdef CONFIG_KASAN
-int kasan_um_is_ready;
-void kasan_init(void)
+void __init kasan_init(void)
{
/*
* kasan_map_memory will map all of the required address space and
@@ -32,7 +32,10 @@ void kasan_init(void)
*/
kasan_map_memory((void *)KASAN_SHADOW_START, KASAN_SHADOW_SIZE);
init_task.kasan_depth = 0;
- kasan_um_is_ready = true;
+ /* Since kasan_init() is called before main(),
+ * KASAN is initialized but the enablement is deferred after
+ * jump_label_init(). See arch_mm_preinit().
+ */
}
static void (*kasan_init_ptr)(void)
@@ -58,6 +61,9 @@ static unsigned long brk_end;
void __init arch_mm_preinit(void)
{
+ /* Safe to call after jump_label_init(). Enables KASAN. */
+ kasan_init_generic();
+
/* clear the zero-page */
memset(empty_zero_page, 0, PAGE_SIZE);
--
2.34.1
