Re: [PATCH 04/11] kasan: add match-all tag tests

On Tue, Jan 12, 2021 at 2:17 PM Marco Elver [off-list ref] wrote:

On Tue, Jan 05, 2021 at 07:27PM +0100, Andrey Konovalov wrote:

quoted

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.

Signed-off-by: Andrey Konovalov <redacted>
Link: https://linux-review.googlesource.com/id/I78f1375efafa162b37f3abcb2c5bc2f3955dfd8e
---
 lib/test_kasan.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++
 mm/kasan/kasan.h |  6 ++++
 2 files changed, 99 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 46e578c8e842..f1eda0bcc780 100644
--- a/lib/test_kasan.c
+++ b/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>

@@ -790,6 +791,95 @@ static void vmalloc_oob(struct kunit *test)
      vfree(area);
 }

+/*
+ * Check that match-all pointer tag is not assigned randomly for
+ * tag-based modes.
+ */
+static void match_all_not_assigned(struct kunit *test)
+{
+     char *ptr;
+     struct page *pages;
+     int i, size, order;
+
+     for (i = 0; i < 256; i++) {
+             size = get_random_int() % KMALLOC_MAX_SIZE;

size appears to be unused?

Indeed, will fix in v2, thanks!

quoted

+             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);
+             kfree(ptr);
+     }
+
+     for (i = 0; i < 256; i++) {
+             order = get_random_int() % 4;
+             pages = alloc_pages(GFP_KERNEL, order);
+             ptr = page_address(pages);
+             KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+             KUNIT_EXPECT_NE(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;
+
+     if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
+             kunit_info(test, "skipping, CONFIG_KASAN_SW/HW_TAGS required");
+             return;
+     }
+
+     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;
+
+     if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
+             kunit_info(test, "skipping, CONFIG_KASAN_SW/HW_TAGS required");
+             return;
+     }
+
+     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),

@@ -829,6 +919,9 @@ 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),
      {}
 };

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 3b38baddec47..c3fb9bf241d3 100644
--- a/mm/kasan/kasan.h
+++ b/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 */
--

2.29.2.729.g45daf8777d-goog