kasan, arm64: only init shadow for software modes

This is a preparatory commit for the upcoming addition of a new hardware
tag-based (MTE-based) KASAN mode.

Hardware tag-based KASAN won't be using shadow memory.  Only initialize it
when one of the software KASAN modes are enabled.

No functional changes for software modes.

Link: https://lkml.kernel.org/r/d1742eea2cd728d150d49b144e49b6433405c7ba.1606161801.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm64/include/asm/kasan.h

@@ -13,6 +13,12 @@
 #define arch_kasan_get_tag(addr)	__tag_get(addr)
 
 #ifdef CONFIG_KASAN
+void kasan_init(void);
+#else
+static inline void kasan_init(void) { }
+#endif
+
+#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 
 /*
  * KASAN_SHADOW_START: beginning of the kernel virtual addresses.
@@ -33,12 +39,10 @@
 #define _KASAN_SHADOW_START(va)	(KASAN_SHADOW_END - (1UL << ((va) - KASAN_SHADOW_SCALE_SHIFT)))
 #define KASAN_SHADOW_START      _KASAN_SHADOW_START(vabits_actual)
 
-void kasan_init(void);
 void kasan_copy_shadow(pgd_t *pgdir);
 asmlinkage void kasan_early_init(void);
 
 #else
-static inline void kasan_init(void) { }
 static inline void kasan_copy_shadow(pgd_t *pgdir) { }
 #endif
 

arch/arm64/mm/kasan_init.c

@@ -21,6 +21,8 @@
 #include <asm/sections.h>
 #include <asm/tlbflush.h>
 
+#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
+
 static pgd_t tmp_pg_dir[PTRS_PER_PGD] __initdata __aligned(PGD_SIZE);
 
 /*
@@ -208,7 +210,7 @@ static void __init clear_pgds(unsigned long start,
 		set_pgd(pgd_offset_k(start), __pgd(0));
 }
 
-void __init kasan_init(void)
+static void __init kasan_init_shadow(void)
 {
 	u64 kimg_shadow_start, kimg_shadow_end;
 	u64 mod_shadow_start, mod_shadow_end;
@@ -269,6 +271,17 @@ void __init kasan_init(void)
 
 	memset(kasan_early_shadow_page, KASAN_SHADOW_INIT, PAGE_SIZE);
 	cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
+}
+
+#else /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS) */
+
+static inline void __init kasan_init_shadow(void) { }
+
+#endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
+
+void __init kasan_init(void)
+{
+	kasan_init_shadow();
 
 	/* At this point kasan is fully initialized. Enable error messages */
 	init_task.kasan_depth = 0;