kasan: add hooks implementation for tag-based mode

This commit adds tag-based KASAN specific hooks implementation and
adjusts common generic and tag-based KASAN ones.

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

2. On each kmalloc tag-based KASAN 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 tag-based KASAN 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 generic KASAN. Tag-based KASAN saves allocation and
free stack metadata to the slab object the same way generic KASAN does.

Link: http://lkml.kernel.org/r/bda78069e3b8422039794050ddcb2d53d053ed41.1544099024.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.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, 48 insertions, 0 deletions

diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 1c4e7ce2e6fe..1d1b79350e28 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -78,15 +78,60 @@ void *kasan_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;
+
+	if (unlikely(size == 0))
+		return;
+
+	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 KASAN_TAG_KERNEL (0xFF)).
+	 */
+	if (tag == KASAN_TAG_KERNEL)
+		return;
+
+	untagged_addr = reset_tag((const void *)addr);
+	if (unlikely(untagged_addr <
+			kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
+		kasan_report(addr, size, write, ret_ip);
+		return;
+	}
+	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)
 
@@ -98,15 +143,18 @@ 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);