[PATCH 3/3] lkdtm/heap: Add tests for freelist hardening

[Kees Cook <keescook@xxxxxxxxxxxx>]

This adds tests for double free and cross-cache freeing, which should
both be caught by CONFIG_SLAB_FREELIST_HARDENED.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 drivers/misc/lkdtm/core.c  |  5 +++
 drivers/misc/lkdtm/heap.c  | 72 ++++++++++++++++++++++++++++++++++++++
 drivers/misc/lkdtm/lkdtm.h |  5 +++
 3 files changed, 82 insertions(+)

diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
index 4f3a6e1cd331..b78df5a09217 100644
--- a/drivers/misc/lkdtm/core.c
+++ b/drivers/misc/lkdtm/core.c
@@ -133,6 +133,9 @@ static const struct crashtype crashtypes[] = {
 	CRASHTYPE(READ_AFTER_FREE),
 	CRASHTYPE(WRITE_BUDDY_AFTER_FREE),
 	CRASHTYPE(READ_BUDDY_AFTER_FREE),
+	CRASHTYPE(SLAB_FREE_DOUBLE),
+	CRASHTYPE(SLAB_FREE_CROSS),
+	CRASHTYPE(SLAB_FREE_PAGE),
 	CRASHTYPE(SOFTLOCKUP),
 	CRASHTYPE(HARDLOCKUP),
 	CRASHTYPE(SPINLOCKUP),
@@ -439,6 +442,7 @@ static int __init lkdtm_module_init(void)
 	lkdtm_bugs_init(&recur_count);
 	lkdtm_perms_init();
 	lkdtm_usercopy_init();
+	lkdtm_heap_init();
 
 	/* Register debugfs interface */
 	lkdtm_debugfs_root = debugfs_create_dir("provoke-crash", NULL);
@@ -485,6 +489,7 @@ static void __exit lkdtm_module_exit(void)
 	debugfs_remove_recursive(lkdtm_debugfs_root);
 
 	/* Handle test-specific clean-up. */
+	lkdtm_heap_exit();
 	lkdtm_usercopy_exit();
 
 	if (lkdtm_kprobe != NULL)
diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c
index 65026d7de130..3c5cec85edce 100644
--- a/drivers/misc/lkdtm/heap.c
+++ b/drivers/misc/lkdtm/heap.c
@@ -7,6 +7,10 @@
 #include <linux/slab.h>
 #include <linux/sched.h>
 
+static struct kmem_cache *double_free_cache;
+static struct kmem_cache *a_cache;
+static struct kmem_cache *b_cache;
+
 /*
  * This tries to stay within the next largest power-of-2 kmalloc cache
  * to avoid actually overwriting anything important if it's not detected
@@ -146,3 +150,71 @@ void lkdtm_READ_BUDDY_AFTER_FREE(void)
 
 	kfree(val);
 }
+
+void lkdtm_SLAB_FREE_DOUBLE(void)
+{
+	int *val;
+
+	val = kmem_cache_alloc(double_free_cache, GFP_KERNEL);
+	if (!val) {
+		pr_info("Unable to allocate double_free_cache memory.\n");
+		return;
+	}
+
+	/* Just make sure we got real memory. */
+	*val = 0x12345678;
+	pr_info("Attempting double slab free ...\n");
+	kmem_cache_free(double_free_cache, val);
+	kmem_cache_free(double_free_cache, val);
+}
+
+void lkdtm_SLAB_FREE_CROSS(void)
+{
+	int *val;
+
+	val = kmem_cache_alloc(a_cache, GFP_KERNEL);
+	if (!val) {
+		pr_info("Unable to allocate a_cache memory.\n");
+		return;
+	}
+
+	/* Just make sure we got real memory. */
+	*val = 0x12345679;
+	pr_info("Attempting cross-cache slab free ...\n");
+	kmem_cache_free(b_cache, val);
+}
+
+void lkdtm_SLAB_FREE_PAGE(void)
+{
+	unsigned long p = __get_free_page(GFP_KERNEL);
+
+	pr_info("Attempting non-Slab slab free ...\n");
+	kmem_cache_free(NULL, (void *)p);
+	free_page(p);
+}
+
+/*
+ * We have constructors to keep the caches distinctly separated without
+ * needing to boot with "slab_nomerge".
+ */
+static void ctor_double_free(void *region)
+{ }
+static void ctor_a(void *region)
+{ }
+static void ctor_b(void *region)
+{ }
+
+void __init lkdtm_heap_init(void)
+{
+	double_free_cache = kmem_cache_create("lkdtm-heap-double_free",
+					      64, 0, 0, ctor_double_free);
+	a_cache = kmem_cache_create("lkdtm-heap-a", 64, 0, 0, ctor_a);
+	b_cache = kmem_cache_create("lkdtm-heap-b", 64, 0, 0, ctor_b);
+}
+
+void __exit lkdtm_heap_exit(void)
+{
+	kmem_cache_destroy(double_free_cache);
+	kmem_cache_destroy(a_cache);
+	kmem_cache_destroy(b_cache);
+}
diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
index 23dc565b4307..c5ae0b37587d 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -28,11 +28,16 @@ void lkdtm_STACK_GUARD_PAGE_LEADING(void);
 void lkdtm_STACK_GUARD_PAGE_TRAILING(void);
 
 /* lkdtm_heap.c */
+void __init lkdtm_heap_init(void);
+void __exit lkdtm_heap_exit(void);
 void lkdtm_OVERWRITE_ALLOCATION(void);
 void lkdtm_WRITE_AFTER_FREE(void);
 void lkdtm_READ_AFTER_FREE(void);
 void lkdtm_WRITE_BUDDY_AFTER_FREE(void);
 void lkdtm_READ_BUDDY_AFTER_FREE(void);
+void lkdtm_SLAB_FREE_DOUBLE(void);
+void lkdtm_SLAB_FREE_CROSS(void);
+void lkdtm_SLAB_FREE_PAGE(void);
 
 /* lkdtm_perms.c */
 void __init lkdtm_perms_init(void);
-- 
2.17.1