[PATCH v4 13/17] khwasan: add hooks implementation

From: Andrey Konovalov
Date: Tue Jun 26 2018 - 09:17:46 EST

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In reply to: Andrey Konovalov: "[PATCH v4 15/17] khwasan, mm, arm64: tag non slab memory allocated via pagealloc"
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This commit adds KHWASAN specific hooks implementation and adjusts
common KASAN and KHWASAN ones.

1. When a new slab cache is created, KHWASAN rounds up the size of the
objects in this cache to KASAN_SHADOW_SCALE_SIZE (== 16).

2. On each kmalloc KHWASAN generates a random tag, sets the shadow memory,
that corresponds to this object to this tag, and embeds this tag value
into the top byte of the returned pointer.

3. On each kfree KHWASAN poisons the shadow memory with a random tag to
allow detection of use-after-free bugs.

The rest of the logic of the hook implementation is very much similar to
the one provided by KASAN. KHWASAN saves allocation and free stack metadata
to the slab object the same was KASAN does this.

Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
mm/kasan/common.c | 83 +++++++++++++++++++++++++++++++++++-----------
mm/kasan/kasan.h | 8 +++++
mm/kasan/khwasan.c | 40 ++++++++++++++++++++++
3 files changed, 111 insertions(+), 20 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 656baa8984c7..1e96ca050c75 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -140,6 +140,9 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value)
{
void *shadow_start, *shadow_end;

+ /* Perform shadow offset calculation based on untagged address */
+ address = reset_tag(address);
+
shadow_start = kasan_mem_to_shadow(address);
shadow_end = kasan_mem_to_shadow(address + size);

@@ -148,11 +151,20 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value)

void kasan_unpoison_shadow(const void *address, size_t size)
{
- kasan_poison_shadow(address, size, 0);
+ u8 tag = get_tag(address);
+
+ /* Perform shadow offset calculation based on untagged address */
+ address = reset_tag(address);
+
+ kasan_poison_shadow(address, size, tag);

if (size & KASAN_SHADOW_MASK) {
u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
- *shadow = size & KASAN_SHADOW_MASK;
+
+ if (IS_ENABLED(CONFIG_KASAN_HW))
+ *shadow = tag;
+ else
+ *shadow = size & KASAN_SHADOW_MASK;
}
}

@@ -200,8 +212,9 @@ void kasan_unpoison_stack_above_sp_to(const void *watermark)

void kasan_alloc_pages(struct page *page, unsigned int order)
{
- if (likely(!PageHighMem(page)))
- kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
+ if (unlikely(PageHighMem(page)))
+ return;
+ kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
}

void kasan_free_pages(struct page *page, unsigned int order)
@@ -235,6 +248,7 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
slab_flags_t *flags)
{
unsigned int orig_size = *size;
+ unsigned int redzone_size = 0;
int redzone_adjust;

/* Add alloc meta. */
@@ -242,20 +256,20 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
*size += sizeof(struct kasan_alloc_meta);

/* Add free meta. */
- if (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
- cache->object_size < sizeof(struct kasan_free_meta)) {
+ if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
+ (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
+ cache->object_size < sizeof(struct kasan_free_meta))) {
cache->kasan_info.free_meta_offset = *size;
*size += sizeof(struct kasan_free_meta);
}
- redzone_adjust = optimal_redzone(cache->object_size) -
- (*size - cache->object_size);

+ redzone_size = optimal_redzone(cache->object_size);
+ redzone_adjust = redzone_size - (*size - cache->object_size);
if (redzone_adjust > 0)
*size += redzone_adjust;

*size = min_t(unsigned int, KMALLOC_MAX_SIZE,
- max(*size, cache->object_size +
- optimal_redzone(cache->object_size)));
+ max(*size, cache->object_size + redzone_size));

/*
* If the metadata doesn't fit, don't enable KASAN at all.
@@ -268,6 +282,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
return;
}

+ cache->align = round_up(cache->align, KASAN_SHADOW_SCALE_SIZE);
+
*flags |= SLAB_KASAN;
}

@@ -325,18 +341,41 @@ void kasan_init_slab_obj(struct kmem_cache *cache, const void *object)

void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
{
- return kasan_kmalloc(cache, object, cache->object_size, flags);
+ object = kasan_kmalloc(cache, object, cache->object_size, flags);
+ if (IS_ENABLED(CONFIG_KASAN_HW) && unlikely(cache->ctor)) {
+ /*
+ * Cache constructor might use object's pointer value to
+ * initialize some of its fields.
+ */
+ cache->ctor(object);
+ }
+ return object;
+}
+
+static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
+{
+ if (IS_ENABLED(CONFIG_KASAN_GENERIC))
+ return shadow_byte < 0 ||
+ shadow_byte >= KASAN_SHADOW_SCALE_SIZE;
+ else
+ return tag != (u8)shadow_byte;
}

static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
unsigned long ip, bool quarantine)
{
s8 shadow_byte;
+ u8 tag;
+ void *tagged_object;
unsigned long rounded_up_size;

+ tag = get_tag(object);
+ tagged_object = object;
+ object = reset_tag(object);
+
if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) !=
object)) {
- kasan_report_invalid_free(object, ip);
+ kasan_report_invalid_free(tagged_object, ip);
return true;
}

@@ -345,20 +384,22 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
return false;

shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
- if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
- kasan_report_invalid_free(object, ip);
+ if (shadow_invalid(tag, shadow_byte)) {
+ kasan_report_invalid_free(tagged_object, ip);
return true;
}

rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE);
kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);

- if (!quarantine || unlikely(!(cache->flags & SLAB_KASAN)))
+ if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
+ unlikely(!(cache->flags & SLAB_KASAN)))
return false;

set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT);
quarantine_put(get_free_info(cache, object), cache);
- return true;
+
+ return IS_ENABLED(CONFIG_KASAN_GENERIC);
}

bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
@@ -371,6 +412,7 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
{
unsigned long redzone_start;
unsigned long redzone_end;
+ u8 tag;

if (gfpflags_allow_blocking(flags))
quarantine_reduce();
@@ -383,14 +425,15 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
redzone_end = round_up((unsigned long)object + cache->object_size,
KASAN_SHADOW_SCALE_SIZE);

- kasan_unpoison_shadow(object, size);
+ tag = random_tag();
+ kasan_unpoison_shadow(set_tag(object, tag), size);
kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
KASAN_KMALLOC_REDZONE);

if (cache->flags & SLAB_KASAN)
set_track(&get_alloc_info(cache, object)->alloc_track, flags);

- return (void *)object;
+ return set_tag(object, tag);
}
EXPORT_SYMBOL(kasan_kmalloc);

@@ -440,7 +483,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
page = virt_to_head_page(ptr);

if (unlikely(!PageSlab(page))) {
- if (ptr != page_address(page)) {
+ if (reset_tag(ptr) != page_address(page)) {
kasan_report_invalid_free(ptr, ip);
return;
}
@@ -453,7 +496,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)

void kasan_kfree_large(void *ptr, unsigned long ip)
{
- if (ptr != page_address(virt_to_head_page(ptr)))
+ if (reset_tag(ptr) != page_address(virt_to_head_page(ptr)))
kasan_report_invalid_free(ptr, ip);
/* The object will be poisoned by page_alloc. */
}
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index d60859d26be7..6f4f2ebf5f57 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -12,10 +12,18 @@
#define KHWASAN_TAG_INVALID 0xFE /* inaccessible memory tag */
#define KHWASAN_TAG_MAX 0xFD /* maximum value for random tags */

+#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) */
+#else
+#define KASAN_FREE_PAGE KHWASAN_TAG_INVALID
+#define KASAN_PAGE_REDZONE KHWASAN_TAG_INVALID
+#define KASAN_KMALLOC_REDZONE KHWASAN_TAG_INVALID
+#define KASAN_KMALLOC_FREE KHWASAN_TAG_INVALID
+#endif
+
#define KASAN_GLOBAL_REDZONE 0xFA /* redzone for global variable */

/*
diff --git a/mm/kasan/khwasan.c b/mm/kasan/khwasan.c
index d34679b8f8c7..fd1725022794 100644
--- a/mm/kasan/khwasan.c
+++ b/mm/kasan/khwasan.c
@@ -88,15 +88,52 @@ void *khwasan_reset_tag(const void *addr)
void check_memory_region(unsigned long addr, size_t size, bool write,
unsigned long ret_ip)
{
+ u8 tag;
+ u8 *shadow_first, *shadow_last, *shadow;
+ void *untagged_addr;
+
+ tag = get_tag((const void *)addr);
+
+ /* Ignore accesses for pointers tagged with 0xff (native kernel
+ * pointer tag) to suppress false positives caused by kmap.
+ *
+ * Some kernel code was written to account for archs that don't keep
+ * high memory mapped all the time, but rather map and unmap particular
+ * pages when needed. Instead of storing a pointer to the kernel memory,
+ * this code saves the address of the page structure and offset within
+ * that page for later use. Those pages are then mapped and unmapped
+ * with kmap/kunmap when necessary and virt_to_page is used to get the
+ * virtual address of the page. For arm64 (that keeps the high memory
+ * mapped all the time), kmap is turned into a page_address call.
+
+ * The issue is that with use of the page_address + virt_to_page
+ * sequence the top byte value of the original pointer gets lost (gets
+ * set to KHWASAN_TAG_KERNEL (0xFF).
+ */
+ if (tag == KHWASAN_TAG_KERNEL)
+ return;
+
+ untagged_addr = reset_tag((const void *)addr);
+ shadow_first = kasan_mem_to_shadow(untagged_addr);
+ shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
+
+ for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
+ if (*shadow != tag) {
+ kasan_report(addr, size, write, ret_ip);
+ return;
+ }
+ }
}

#define DEFINE_HWASAN_LOAD_STORE(size) \
void __hwasan_load##size##_noabort(unsigned long addr) \
{ \
+ check_memory_region(addr, size, false, _RET_IP_); \
} \
EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
void __hwasan_store##size##_noabort(unsigned long addr) \
{ \
+ check_memory_region(addr, size, true, _RET_IP_); \
} \
EXPORT_SYMBOL(__hwasan_store##size##_noabort)

@@ -108,15 +145,18 @@ DEFINE_HWASAN_LOAD_STORE(16);

void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
{
+ check_memory_region(addr, size, false, _RET_IP_);
}
EXPORT_SYMBOL(__hwasan_loadN_noabort);

void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
{
+ check_memory_region(addr, size, true, _RET_IP_);
}
EXPORT_SYMBOL(__hwasan_storeN_noabort);

void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
{
+ kasan_poison_shadow((void *)addr, size, tag);
}
EXPORT_SYMBOL(__hwasan_tag_memory);
--
2.18.0.rc2.346.g013aa6912e-goog

Next message: Andrey Konovalov: "[PATCH v4 14/17] khwasan, arm64: add brk handler for inline instrumentation"
Previous message: Liviu Dudau: "Re: [RFC PATCH 3/4] drm/arm/malidp: Set the AFBC register bits if the framebuffer has AFBC modifier"
In reply to: Andrey Konovalov: "[PATCH v4 15/17] khwasan, mm, arm64: tag non slab memory allocated via pagealloc"
Next in thread: Andrey Konovalov: "[PATCH v4 14/17] khwasan, arm64: add brk handler for inline instrumentation"
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