kasan: add and integrate kasan boot parameters

Hardware tag-based KASAN mode is intended to eventually be used in
production as a security mitigation. Therefore there's a need for finer
control over KASAN features and for an existence of a kill switch.

This change adds a few boot parameters for hardware tag-based KASAN that
allow to disable or otherwise control particular KASAN features.

The features that can be controlled are:

1. Whether KASAN is enabled at all.
2. Whether KASAN collects and saves alloc/free stacks.
3. Whether KASAN panics on a detected bug or not.

With this change a new boot parameter kasan.mode allows to choose one of
three main modes:

- kasan.mode=off - KASAN is disabled, no tag checks are performed
- kasan.mode=prod - only essential production features are enabled
- kasan.mode=full - all KASAN features are enabled

The chosen mode provides default control values for the features mentioned
above. However it's also possible to override the default values by
providing:

- kasan.stacktrace=off/on - enable alloc/free stack collection
                            (default: on for mode=full, otherwise off)
- kasan.fault=report/panic - only report tag fault or also panic
                             (default: report)

If kasan.mode parameter is not provided, it defaults to full when
CONFIG_DEBUG_KERNEL is enabled, and to prod otherwise.

It is essential that switching between these modes doesn't require
rebuilding the kernel with different configs, as this is required by
the Android GKI (Generic Kernel Image) initiative [1].

[1] https://source.android.com/devices/architecture/kernel/generic-kernel-image

[andreyknvl@google.com: don't use read-only static keys]
  Link: https://lkml.kernel.org/r/f2ded589eba1597f7360a972226083de9afd86e2.1607537948.git.andreyknvl@google.com

Link: https://lkml.kernel.org/r/cb093613879d8d8841173f090133eddeb4c35f1f.1606162397.git.andreyknvl@google.com
Link: https://linux-review.googlesource.com/id/If7d37003875b2ed3e0935702c8015c223d6416a4
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.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>

1 files changed, 17 insertions, 5 deletions

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 780ec27459ab..219c2979bd3e 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -134,6 +134,11 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
 	unsigned int redzone_size;
 	int redzone_adjust;
 
+	if (!kasan_stack_collection_enabled()) {
+		*flags |= SLAB_KASAN;
+		return;
+	}
+
 	/* Add alloc meta. */
 	cache->kasan_info.alloc_meta_offset = *size;
 	*size += sizeof(struct kasan_alloc_meta);
@@ -170,6 +175,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
 
 size_t kasan_metadata_size(struct kmem_cache *cache)
 {
+	if (!kasan_stack_collection_enabled())
+		return 0;
 	return (cache->kasan_info.alloc_meta_offset ?
 		sizeof(struct kasan_alloc_meta) : 0) +
 		(cache->kasan_info.free_meta_offset ?
@@ -262,11 +269,13 @@ void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
 {
 	struct kasan_alloc_meta *alloc_meta;
 
-	if (!(cache->flags & SLAB_KASAN))
-		return (void *)object;
+	if (kasan_stack_collection_enabled()) {
+		if (!(cache->flags & SLAB_KASAN))
+			return (void *)object;
 
-	alloc_meta = kasan_get_alloc_meta(cache, object);
-	__memset(alloc_meta, 0, sizeof(*alloc_meta));
+		alloc_meta = kasan_get_alloc_meta(cache, object);
+		__memset(alloc_meta, 0, sizeof(*alloc_meta));
+	}
 
 	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
 		object = set_tag(object, assign_tag(cache, object, true, false));
@@ -303,6 +312,9 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
 	rounded_up_size = round_up(cache->object_size, KASAN_GRANULE_SIZE);
 	poison_range(object, rounded_up_size, KASAN_KMALLOC_FREE);
 
+	if (!kasan_stack_collection_enabled())
+		return false;
+
 	if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
 			unlikely(!(cache->flags & SLAB_KASAN)))
 		return false;
@@ -350,7 +362,7 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
 	poison_range((void *)redzone_start, redzone_end - redzone_start,
 		     KASAN_KMALLOC_REDZONE);
 
-	if (cache->flags & SLAB_KASAN)
+	if (kasan_stack_collection_enabled() && (cache->flags & SLAB_KASAN))
 		set_alloc_info(cache, (void *)object, flags);
 
 	return set_tag(object, tag);