kasan: add match-all tag tests

Add 3 new tests for tag-based KASAN modes:

1. Check that match-all pointer tag is not assigned randomly.
2. Check that 0xff works as a match-all pointer tag.
3. Check that there are no match-all memory tags.

Note, that test #3 causes a significant number (255) of KASAN reports
to be printed during execution for the SW_TAGS mode.

[arnd@arndb.de: export kasan_poison]
  Link: https://lkml.kernel.org/r/20210125112831.2156212-1-arnd@kernel.org
[akpm@linux-foundation.org: s/EXPORT_SYMBOL_GPL/EXPORT_SYMBOL/, per Andrey]

Link: https://linux-review.googlesource.com/id/I78f1375efafa162b37f3abcb2c5bc2f3955dfd8e
Link: https://lkml.kernel.org/r/da841a5408e2204bf25f3b23f70540a65844e8a4.1610733117.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: 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: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@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>

lib/test_kasan.c

@@ -13,6 +13,7 @@
 #include <linux/mman.h>
 #include <linux/module.h>
 #include <linux/printk.h>
+#include <linux/random.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/uaccess.h>
@@ -754,6 +755,94 @@ static void vmalloc_oob(struct kunit *test)
 	vfree(area);
 }
 
+/*
+ * Check that the assigned pointer tag falls within the [KASAN_TAG_MIN,
+ * KASAN_TAG_KERNEL) range (note: excluding the match-all tag) for tag-based
+ * modes.
+ */
+static void match_all_not_assigned(struct kunit *test)
+{
+	char *ptr;
+	struct page *pages;
+	int i, size, order;
+
+	KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_GENERIC);
+
+	for (i = 0; i < 256; i++) {
+		size = (get_random_int() % 1024) + 1;
+		ptr = kmalloc(size, GFP_KERNEL);
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+		KUNIT_EXPECT_GE(test, (u8)get_tag(ptr), (u8)KASAN_TAG_MIN);
+		KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL);
+		kfree(ptr);
+	}
+
+	for (i = 0; i < 256; i++) {
+		order = (get_random_int() % 4) + 1;
+		pages = alloc_pages(GFP_KERNEL, order);
+		ptr = page_address(pages);
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+		KUNIT_EXPECT_GE(test, (u8)get_tag(ptr), (u8)KASAN_TAG_MIN);
+		KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL);
+		free_pages((unsigned long)ptr, order);
+	}
+}
+
+/* Check that 0xff works as a match-all pointer tag for tag-based modes. */
+static void match_all_ptr_tag(struct kunit *test)
+{
+	char *ptr;
+	u8 tag;
+
+	KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_GENERIC);
+
+	ptr = kmalloc(128, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+
+	/* Backup the assigned tag. */
+	tag = get_tag(ptr);
+	KUNIT_EXPECT_NE(test, tag, (u8)KASAN_TAG_KERNEL);
+
+	/* Reset the tag to 0xff.*/
+	ptr = set_tag(ptr, KASAN_TAG_KERNEL);
+
+	/* This access shouldn't trigger a KASAN report. */
+	*ptr = 0;
+
+	/* Recover the pointer tag and free. */
+	ptr = set_tag(ptr, tag);
+	kfree(ptr);
+}
+
+/* Check that there are no match-all memory tags for tag-based modes. */
+static void match_all_mem_tag(struct kunit *test)
+{
+	char *ptr;
+	int tag;
+
+	KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_GENERIC);
+
+	ptr = kmalloc(128, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+	KUNIT_EXPECT_NE(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL);
+
+	/* For each possible tag value not matching the pointer tag. */
+	for (tag = KASAN_TAG_MIN; tag <= KASAN_TAG_KERNEL; tag++) {
+		if (tag == get_tag(ptr))
+			continue;
+
+		/* Mark the first memory granule with the chosen memory tag. */
+		kasan_poison(ptr, KASAN_GRANULE_SIZE, (u8)tag);
+
+		/* This access must cause a KASAN report. */
+		KUNIT_EXPECT_KASAN_FAIL(test, *ptr = 0);
+	}
+
+	/* Recover the memory tag and free. */
+	kasan_poison(ptr, KASAN_GRANULE_SIZE, get_tag(ptr));
+	kfree(ptr);
+}
+
 static struct kunit_case kasan_kunit_test_cases[] = {
 	KUNIT_CASE(kmalloc_oob_right),
 	KUNIT_CASE(kmalloc_oob_left),
@@ -793,6 +882,9 @@ static struct kunit_case kasan_kunit_test_cases[] = {
 	KUNIT_CASE(kasan_bitops_tags),
 	KUNIT_CASE(kmalloc_double_kzfree),
 	KUNIT_CASE(vmalloc_oob),
+	KUNIT_CASE(match_all_not_assigned),
+	KUNIT_CASE(match_all_ptr_tag),
+	KUNIT_CASE(match_all_mem_tag),
 	{}
 };
 

mm/kasan/kasan.h

@@ -36,6 +36,12 @@ extern bool kasan_flag_panic __ro_after_init;
 #define KASAN_TAG_INVALID	0xFE /* inaccessible memory tag */
 #define KASAN_TAG_MAX		0xFD /* maximum value for random tags */
 
+#ifdef CONFIG_KASAN_HW_TAGS
+#define KASAN_TAG_MIN		0xF0 /* mimimum value for random tags */
+#else
+#define KASAN_TAG_MIN		0x00 /* mimimum value for random tags */
+#endif
+
 #ifdef CONFIG_KASAN_GENERIC
 #define KASAN_FREE_PAGE         0xFF  /* page was freed */
 #define KASAN_PAGE_REDZONE      0xFE  /* redzone for kmalloc_large allocations */

mm/kasan/shadow.c

@@ -89,6 +89,7 @@ void kasan_poison(const void *address, size_t size, u8 value)
 
 	__memset(shadow_start, value, shadow_end - shadow_start);
 }
+EXPORT_SYMBOL(kasan_poison);
 
 void kasan_unpoison(const void *address, size_t size)
 {