kasan: clean up comments in internal kasan.h

Clean up comments in mm/kasan/kasan.h: clarify, unify styles, fix
punctuation, etc.

Link: https://lkml.kernel.org/r/a0680ff30035b56cb7bdd5f59fd400e71712ceb5.1652111464.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/kasan/kasan.h

@@ -42,6 +42,7 @@ static inline bool kasan_sync_fault_possible(void)
 {
 	return kasan_mode == KASAN_MODE_SYNC || kasan_mode == KASAN_MODE_ASYMM;
 }
+
 #else
 
 static inline bool kasan_stack_collection_enabled(void)
@@ -73,47 +74,41 @@ static inline bool kasan_sync_fault_possible(void)
 #define KASAN_MEMORY_PER_SHADOW_PAGE	(KASAN_GRANULE_SIZE << PAGE_SHIFT)
 
 #ifdef CONFIG_KASAN_GENERIC
-#define KASAN_FREE_PAGE         0xFF  /* page was freed */
-#define KASAN_PAGE_REDZONE      0xFE  /* redzone for kmalloc_large allocations */
-#define KASAN_KMALLOC_REDZONE   0xFC  /* redzone inside slub object */
-#define KASAN_KMALLOC_FREE      0xFB  /* object was freed (kmem_cache_free/kfree) */
-#define KASAN_VMALLOC_INVALID   0xF8  /* unallocated space in vmapped page */
+#define KASAN_FREE_PAGE         0xFF  /* freed page */
+#define KASAN_PAGE_REDZONE      0xFE  /* redzone for kmalloc_large allocation */
+#define KASAN_KMALLOC_REDZONE   0xFC  /* redzone for slab object */
+#define KASAN_KMALLOC_FREE      0xFB  /* freed slab object */
+#define KASAN_VMALLOC_INVALID   0xF8  /* inaccessible space in vmap area */
 #else
 #define KASAN_FREE_PAGE         KASAN_TAG_INVALID
 #define KASAN_PAGE_REDZONE      KASAN_TAG_INVALID
 #define KASAN_KMALLOC_REDZONE   KASAN_TAG_INVALID
 #define KASAN_KMALLOC_FREE      KASAN_TAG_INVALID
-#define KASAN_VMALLOC_INVALID   KASAN_TAG_INVALID /* only for SW_TAGS */
+#define KASAN_VMALLOC_INVALID   KASAN_TAG_INVALID /* only used for SW_TAGS */
 #endif
 
 #ifdef CONFIG_KASAN_GENERIC
 
-#define KASAN_KMALLOC_FREETRACK 0xFA  /* object was freed and has free track set */
+#define KASAN_KMALLOC_FREETRACK 0xFA  /* freed slab object with free track */
 #define KASAN_GLOBAL_REDZONE    0xF9  /* redzone for global variable */
 
-/*
- * Stack redzone shadow values
- * (Those are compiler's ABI, don't change them)
- */
+/* Stack redzone shadow values. Compiler ABI, do not change. */
 #define KASAN_STACK_LEFT        0xF1
 #define KASAN_STACK_MID         0xF2
 #define KASAN_STACK_RIGHT       0xF3
 #define KASAN_STACK_PARTIAL     0xF4
 
-/*
- * alloca redzone shadow values
- */
+/* alloca redzone shadow values. */
 #define KASAN_ALLOCA_LEFT	0xCA
 #define KASAN_ALLOCA_RIGHT	0xCB
 
+/* alloca redzone size. Compiler ABI, do not change. */
 #define KASAN_ALLOCA_REDZONE_SIZE	32
 
-/*
- * Stack frame marker (compiler ABI).
- */
+/* Stack frame marker. Compiler ABI, do not change. */
 #define KASAN_CURRENT_STACK_FRAME_MAGIC 0x41B58AB3
 
-/* Don't break randconfig/all*config builds */
+/* Dummy value to avoid breaking randconfig/all*config builds. */
 #ifndef KASAN_ABI_VERSION
 #define KASAN_ABI_VERSION 1
 #endif
@@ -141,21 +136,21 @@ struct kasan_report_info {
 	unsigned long ip;
 };
 
-/* The layout of struct dictated by compiler */
+/* Do not change the struct layout: compiler ABI. */
 struct kasan_source_location {
 	const char *filename;
 	int line_no;
 	int column_no;
 };
 
-/* The layout of struct dictated by compiler */
+/* Do not change the struct layout: compiler ABI. */
 struct kasan_global {
 	const void *beg;		/* Address of the beginning of the global variable. */
 	size_t size;			/* Size of the global variable. */
-	size_t size_with_redzone;	/* Size of the variable + size of the red zone. 32 bytes aligned */
+	size_t size_with_redzone;	/* Size of the variable + size of the redzone. 32 bytes aligned. */
 	const void *name;
 	const void *module_name;	/* Name of the module where the global variable is declared. */
-	unsigned long has_dynamic_init;	/* This needed for C++ */
+	unsigned long has_dynamic_init;	/* This is needed for C++. */
 #if KASAN_ABI_VERSION >= 4
 	struct kasan_source_location *location;
 #endif
@@ -164,9 +159,7 @@ struct kasan_global {
 #endif
 };
 
-/**
- * Structures to keep alloc and free tracks *
- */
+/* Structures for keeping alloc and free tracks. */
 
 #define KASAN_STACK_DEPTH 64
 
@@ -183,11 +176,8 @@ struct kasan_track {
 
 struct kasan_alloc_meta {
 	struct kasan_track alloc_track;
+	/* Generic mode stores free track in kasan_free_meta. */
 #ifdef CONFIG_KASAN_GENERIC
-	/*
-	 * The auxiliary stack is stored into struct kasan_alloc_meta.
-	 * The free stack is stored into struct kasan_free_meta.
-	 */
 	depot_stack_handle_t aux_stack[2];
 #else
 	struct kasan_track free_track[KASAN_NR_FREE_STACKS];
@@ -203,18 +193,18 @@ struct qlist_node {
 };
 
 /*
- * Generic mode either stores free meta in the object itself or in the redzone
- * after the object. In the former case free meta offset is 0, in the latter
- * case it has some sane value smaller than INT_MAX. Use INT_MAX as free meta
- * offset when free meta isn't present.
+ * Free meta is stored either in the object itself or in the redzone after the
+ * object. In the former case, free meta offset is 0. In the latter case, the
+ * offset is between 0 and INT_MAX. INT_MAX marks that free meta is not present.
  */
 #define KASAN_NO_FREE_META INT_MAX
 
+/*
+ * Free meta is only used by Generic mode while the object is in quarantine.
+ * After that, slab allocator stores the freelist pointer in the object.
+ */
 struct kasan_free_meta {
 #ifdef CONFIG_KASAN_GENERIC
-	/* This field is used while the object is in the quarantine.
-	 * Otherwise it might be used for the allocator freelist.
-	 */
 	struct qlist_node quarantine_link;
 	struct kasan_track free_track;
 #endif
@@ -417,9 +407,10 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init)
 		return;
 	/*
 	 * Explicitly initialize the memory with the precise object size to
-	 * avoid overwriting the SLAB redzone. This disables initialization in
-	 * the arch code and may thus lead to performance penalty. The penalty
-	 * is accepted since SLAB redzones aren't enabled in production builds.
+	 * avoid overwriting the slab redzone. This disables initialization in
+	 * the arch code and may thus lead to performance penalty. This penalty
+	 * does not affect production builds, as slab redzones are not enabled
+	 * there.
 	 */
 	if (__slub_debug_enabled() &&
 	    init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
@@ -503,8 +494,9 @@ void kasan_restore_multi_shot(bool enabled);
 
 /*
  * Exported functions for interfaces called from assembly or from generated
- * code. Declarations here to avoid warning about missing declarations.
+ * code. Declared here to avoid warnings about missing declarations.
  */
+
 asmlinkage void kasan_unpoison_task_stack_below(const void *watermark);
 void __asan_register_globals(struct kasan_global *globals, size_t size);
 void __asan_unregister_globals(struct kasan_global *globals, size_t size);
@@ -573,4 +565,4 @@ void __hwasan_storeN_noabort(unsigned long addr, size_t size);
 
 void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size);
 
-#endif
+#endif /* __MM_KASAN_KASAN_H */