[PATCH v5 0/5] Add object validation in ksize()

[PATCH v5 0/5] Add object validation in ksize()

[Marco Elver]

This version fixes several build issues --
Reported-by: kbuild test robot <lkp@intel.com>

Previous version here:
http://lkml.kernel.org/r/20190627094445.216365-1-elver@google.com

Marco Elver (5):
  mm/kasan: Introduce __kasan_check_{read,write}
  mm/kasan: Change kasan_check_{read,write} to return boolean
  lib/test_kasan: Add test for double-kzfree detection
  mm/slab: Refactor common ksize KASAN logic into slab_common.c
  mm/kasan: Add object validation in ksize()

 include/linux/kasan-checks.h | 43 +++++++++++++++++++++++++++------
 include/linux/kasan.h        |  7 ++++--
 include/linux/slab.h         |  1 +
 lib/test_kasan.c             | 17 +++++++++++++
 mm/kasan/common.c            | 14 +++++------
 mm/kasan/generic.c           | 13 +++++-----
 mm/kasan/kasan.h             | 10 +++++++-
 mm/kasan/tags.c              | 12 ++++++----
 mm/slab.c                    | 28 +++++-----------------
 mm/slab_common.c             | 46 ++++++++++++++++++++++++++++++++++++
 mm/slob.c                    |  4 ++--
 mm/slub.c                    | 14 ++---------
 12 files changed, 144 insertions(+), 65 deletions(-)

-- 
2.22.0.410.gd8fdbe21b5-goog

[PATCH v5 1/5] mm/kasan: Introduce __kasan_check_{read,write}

[Marco Elver]

This introduces __kasan_check_{read,write}. __kasan_check functions may
be used from anywhere, even compilation units that disable
instrumentation selectively.

This change eliminates the need for the __KASAN_INTERNAL definition.

Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Qian Cai <cai@lca.pw>
Cc: kasan-dev@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
v5:
* Use #define for kasan_check_* in the __SANITIZE_ADDRESS__ case, as the
  inline functions conflict with the __no_sanitize_address attribute.
  Reported-by: kbuild test robot <lkp@intel.com>

v3:
* Fix Formatting and split introduction of __kasan_check_* and returning
  bool into 2 patches.
---
 include/linux/kasan-checks.h | 25 ++++++++++++++++++++++---
 mm/kasan/common.c            | 10 ++++------
 2 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/include/linux/kasan-checks.h b/include/linux/kasan-checks.h
index a61dc075e2ce..221f05fbddd7 100644
--- a/include/linux/kasan-checks.h
+++ b/include/linux/kasan-checks.h
@@ -2,9 +2,28 @@
 #ifndef _LINUX_KASAN_CHECKS_H
 #define _LINUX_KASAN_CHECKS_H
 
-#if defined(__SANITIZE_ADDRESS__) || defined(__KASAN_INTERNAL)
-void kasan_check_read(const volatile void *p, unsigned int size);
-void kasan_check_write(const volatile void *p, unsigned int size);
+/*
+ * __kasan_check_*: Always available when KASAN is enabled. This may be used
+ * even in compilation units that selectively disable KASAN, but must use KASAN
+ * to validate access to an address.   Never use these in header files!
+ */
+#ifdef CONFIG_KASAN
+void __kasan_check_read(const volatile void *p, unsigned int size);
+void __kasan_check_write(const volatile void *p, unsigned int size);
+#else
+static inline void __kasan_check_read(const volatile void *p, unsigned int size)
+{ }
+static inline void __kasan_check_write(const volatile void *p, unsigned int size)
+{ }
+#endif
+
+/*
+ * kasan_check_*: Only available when the particular compilation unit has KASAN
+ * instrumentation enabled. May be used in header files.
+ */
+#ifdef __SANITIZE_ADDRESS__
+#define kasan_check_read __kasan_check_read
+#define kasan_check_write __kasan_check_write
 #else
 static inline void kasan_check_read(const volatile void *p, unsigned int size)
 { }
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 242fdc01aaa9..6bada42cc152 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -14,8 +14,6 @@
  *
  */
 
-#define __KASAN_INTERNAL
-
 #include <linux/export.h>
 #include <linux/interrupt.h>
 #include <linux/init.h>
@@ -89,17 +87,17 @@ void kasan_disable_current(void)
 	current->kasan_depth--;
 }
 
-void kasan_check_read(const volatile void *p, unsigned int size)
+void __kasan_check_read(const volatile void *p, unsigned int size)
 {
 	check_memory_region((unsigned long)p, size, false, _RET_IP_);
 }
-EXPORT_SYMBOL(kasan_check_read);
+EXPORT_SYMBOL(__kasan_check_read);
 
-void kasan_check_write(const volatile void *p, unsigned int size)
+void __kasan_check_write(const volatile void *p, unsigned int size)
 {
 	check_memory_region((unsigned long)p, size, true, _RET_IP_);
 }
-EXPORT_SYMBOL(kasan_check_write);
+EXPORT_SYMBOL(__kasan_check_write);
 
 #undef memset
 void *memset(void *addr, int c, size_t len)
-- 
2.22.0.410.gd8fdbe21b5-goog

[PATCH v5 2/5] mm/kasan: Change kasan_check_{read,write} to return boolean

[Marco Elver]

This changes {,__}kasan_check_{read,write} functions to return a boolean
denoting if the access was valid or not.

Signed-off-by: Marco Elver <elver@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: kasan-dev@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
v5:
* Rebase on top of v5 of preceding patch.
* Include types.h for bool.

v3:
* Fix Formatting and split introduction of __kasan_check_* and returning
  bool into 2 patches.
---
 include/linux/kasan-checks.h | 30 ++++++++++++++++++++----------
 mm/kasan/common.c            |  8 ++++----
 mm/kasan/generic.c           | 13 +++++++------
 mm/kasan/kasan.h             | 10 +++++++++-
 mm/kasan/tags.c              | 12 +++++++-----
 5 files changed, 47 insertions(+), 26 deletions(-)

diff --git a/include/linux/kasan-checks.h b/include/linux/kasan-checks.h
index 221f05fbddd7..ac6aba632f2d 100644
--- a/include/linux/kasan-checks.h
+++ b/include/linux/kasan-checks.h
@@ -2,19 +2,25 @@
 #ifndef _LINUX_KASAN_CHECKS_H
 #define _LINUX_KASAN_CHECKS_H
 
+#include <linux/types.h>
+
 /*
  * __kasan_check_*: Always available when KASAN is enabled. This may be used
  * even in compilation units that selectively disable KASAN, but must use KASAN
  * to validate access to an address.   Never use these in header files!
  */
 #ifdef CONFIG_KASAN
-void __kasan_check_read(const volatile void *p, unsigned int size);
-void __kasan_check_write(const volatile void *p, unsigned int size);
+bool __kasan_check_read(const volatile void *p, unsigned int size);
+bool __kasan_check_write(const volatile void *p, unsigned int size);
 #else
-static inline void __kasan_check_read(const volatile void *p, unsigned int size)
-{ }
-static inline void __kasan_check_write(const volatile void *p, unsigned int size)
-{ }
+static inline bool __kasan_check_read(const volatile void *p, unsigned int size)
+{
+	return true;
+}
+static inline bool __kasan_check_write(const volatile void *p, unsigned int size)
+{
+	return true;
+}
 #endif
 
 /*
@@ -25,10 +31,14 @@ static inline void __kasan_check_write(const volatile void *p, unsigned int size
 #define kasan_check_read __kasan_check_read
 #define kasan_check_write __kasan_check_write
 #else
-static inline void kasan_check_read(const volatile void *p, unsigned int size)
-{ }
-static inline void kasan_check_write(const volatile void *p, unsigned int size)
-{ }
+static inline bool kasan_check_read(const volatile void *p, unsigned int size)
+{
+	return true;
+}
+static inline bool kasan_check_write(const volatile void *p, unsigned int size)
+{
+	return true;
+}
 #endif
 
 #endif
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 6bada42cc152..2277b82902d8 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -87,15 +87,15 @@ void kasan_disable_current(void)
 	current->kasan_depth--;
 }
 
-void __kasan_check_read(const volatile void *p, unsigned int size)
+bool __kasan_check_read(const volatile void *p, unsigned int size)
 {
-	check_memory_region((unsigned long)p, size, false, _RET_IP_);
+	return check_memory_region((unsigned long)p, size, false, _RET_IP_);
 }
 EXPORT_SYMBOL(__kasan_check_read);
 
-void __kasan_check_write(const volatile void *p, unsigned int size)
+bool __kasan_check_write(const volatile void *p, unsigned int size)
 {
-	check_memory_region((unsigned long)p, size, true, _RET_IP_);
+	return check_memory_region((unsigned long)p, size, true, _RET_IP_);
 }
 EXPORT_SYMBOL(__kasan_check_write);
 
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 504c79363a34..616f9dd82d12 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -166,29 +166,30 @@ static __always_inline bool memory_is_poisoned(unsigned long addr, size_t size)
 	return memory_is_poisoned_n(addr, size);
 }
 
-static __always_inline void check_memory_region_inline(unsigned long addr,
+static __always_inline bool check_memory_region_inline(unsigned long addr,
 						size_t size, bool write,
 						unsigned long ret_ip)
 {
 	if (unlikely(size == 0))
-		return;
+		return true;
 
 	if (unlikely((void *)addr <
 		kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
 		kasan_report(addr, size, write, ret_ip);
-		return;
+		return false;
 	}
 
 	if (likely(!memory_is_poisoned(addr, size)))
-		return;
+		return true;
 
 	kasan_report(addr, size, write, ret_ip);
+	return false;
 }
 
-void check_memory_region(unsigned long addr, size_t size, bool write,
+bool check_memory_region(unsigned long addr, size_t size, bool write,
 				unsigned long ret_ip)
 {
-	check_memory_region_inline(addr, size, write, ret_ip);
+	return check_memory_region_inline(addr, size, write, ret_ip);
 }
 
 void kasan_cache_shrink(struct kmem_cache *cache)
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 3ce956efa0cb..e62ea45d02e3 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -123,7 +123,15 @@ static inline bool addr_has_shadow(const void *addr)
 
 void kasan_poison_shadow(const void *address, size_t size, u8 value);
 
-void check_memory_region(unsigned long addr, size_t size, bool write,
+/**
+ * check_memory_region - Check memory region, and report if invalid access.
+ * @addr: the accessed address
+ * @size: the accessed size
+ * @write: true if access is a write access
+ * @ret_ip: return address
+ * @return: true if access was valid, false if invalid
+ */
+bool check_memory_region(unsigned long addr, size_t size, bool write,
 				unsigned long ret_ip);
 
 void *find_first_bad_addr(void *addr, size_t size);
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 63fca3172659..0e987c9ca052 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -76,7 +76,7 @@ void *kasan_reset_tag(const void *addr)
 	return reset_tag(addr);
 }
 
-void check_memory_region(unsigned long addr, size_t size, bool write,
+bool check_memory_region(unsigned long addr, size_t size, bool write,
 				unsigned long ret_ip)
 {
 	u8 tag;
@@ -84,7 +84,7 @@ void check_memory_region(unsigned long addr, size_t size, bool write,
 	void *untagged_addr;
 
 	if (unlikely(size == 0))
-		return;
+		return true;
 
 	tag = get_tag((const void *)addr);
 
@@ -106,22 +106,24 @@ void check_memory_region(unsigned long addr, size_t size, bool write,
 	 * set to KASAN_TAG_KERNEL (0xFF)).
 	 */
 	if (tag == KASAN_TAG_KERNEL)
-		return;
+		return true;
 
 	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;
+		return false;
 	}
 	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;
+			return false;
 		}
 	}
+
+	return true;
 }
 
 #define DEFINE_HWASAN_LOAD_STORE(size)					\
-- 
2.22.0.410.gd8fdbe21b5-goog

[PATCH v5 3/5] lib/test_kasan: Add test for double-kzfree detection

[Marco Elver]

Adds a simple test that checks if double-kzfree is being detected
correctly.

Signed-off-by: Marco Elver <elver@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: kasan-dev@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
 lib/test_kasan.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index e3c593c38eff..dda5da9f5bd4 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -619,6 +619,22 @@ static noinline void __init kasan_strings(void)
 	strnlen(ptr, 1);
 }
 
+static noinline void __init kmalloc_double_kzfree(void)
+{
+	char *ptr;
+	size_t size = 16;
+
+	pr_info("double-free (kzfree)\n");
+	ptr = kmalloc(size, GFP_KERNEL);
+	if (!ptr) {
+		pr_err("Allocation failed\n");
+		return;
+	}
+
+	kzfree(ptr);
+	kzfree(ptr);
+}
+
 static int __init kmalloc_tests_init(void)
 {
 	/*
@@ -660,6 +676,7 @@ static int __init kmalloc_tests_init(void)
 	kasan_memchr();
 	kasan_memcmp();
 	kasan_strings();
+	kmalloc_double_kzfree();
 
 	kasan_restore_multi_shot(multishot);
 
-- 
2.22.0.410.gd8fdbe21b5-goog

[PATCH v5 4/5] mm/slab: Refactor common ksize KASAN logic into slab_common.c

[Marco Elver]

This refactors common code of ksize() between the various allocators
into slab_common.c: __ksize() is the allocator-specific implementation
without instrumentation, whereas ksize() includes the required KASAN
logic.

Signed-off-by: Marco Elver <elver@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: kasan-dev@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
 include/linux/slab.h |  1 +
 mm/slab.c            | 28 ++++++----------------------
 mm/slab_common.c     | 26 ++++++++++++++++++++++++++
 mm/slob.c            |  4 ++--
 mm/slub.c            | 14 ++------------
 5 files changed, 37 insertions(+), 36 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 9449b19c5f10..98c3d12b7275 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -184,6 +184,7 @@ void * __must_check __krealloc(const void *, size_t, gfp_t);
 void * __must_check krealloc(const void *, size_t, gfp_t);
 void kfree(const void *);
 void kzfree(const void *);
+size_t __ksize(const void *);
 size_t ksize(const void *);
 
 #ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR
diff --git a/mm/slab.c b/mm/slab.c
index f7117ad9b3a3..394e7c7a285e 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -4204,33 +4204,17 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 #endif /* CONFIG_HARDENED_USERCOPY */
 
 /**
- * ksize - get the actual amount of memory allocated for a given object
- * @objp: Pointer to the object
+ * __ksize -- Uninstrumented ksize.
  *
- * kmalloc may internally round up allocations and return more memory
- * than requested. ksize() can be used to determine the actual amount of
- * memory allocated. The caller may use this additional memory, even though
- * a smaller amount of memory was initially specified with the kmalloc call.
- * The caller must guarantee that objp points to a valid object previously
- * allocated with either kmalloc() or kmem_cache_alloc(). The object
- * must not be freed during the duration of the call.
- *
- * Return: size of the actual memory used by @objp in bytes
+ * Unlike ksize(), __ksize() is uninstrumented, and does not provide the same
+ * safety checks as ksize() with KASAN instrumentation enabled.
  */
-size_t ksize(const void *objp)
+size_t __ksize(const void *objp)
 {
-	size_t size;
-
 	BUG_ON(!objp);
 	if (unlikely(objp == ZERO_SIZE_PTR))
 		return 0;
 
-	size = virt_to_cache(objp)->object_size;
-	/* We assume that ksize callers could use the whole allocated area,
-	 * so we need to unpoison this area.
-	 */
-	kasan_unpoison_shadow(objp, size);
-
-	return size;
+	return virt_to_cache(objp)->object_size;
 }
-EXPORT_SYMBOL(ksize);
+EXPORT_SYMBOL(__ksize);
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 58251ba63e4a..b7c6a40e436a 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1597,6 +1597,32 @@ void kzfree(const void *p)
 }
 EXPORT_SYMBOL(kzfree);
 
+/**
+ * ksize - get the actual amount of memory allocated for a given object
+ * @objp: Pointer to the object
+ *
+ * kmalloc may internally round up allocations and return more memory
+ * than requested. ksize() can be used to determine the actual amount of
+ * memory allocated. The caller may use this additional memory, even though
+ * a smaller amount of memory was initially specified with the kmalloc call.
+ * The caller must guarantee that objp points to a valid object previously
+ * allocated with either kmalloc() or kmem_cache_alloc(). The object
+ * must not be freed during the duration of the call.
+ *
+ * Return: size of the actual memory used by @objp in bytes
+ */
+size_t ksize(const void *objp)
+{
+	size_t size = __ksize(objp);
+	/*
+	 * We assume that ksize callers could use whole allocated area,
+	 * so we need to unpoison this area.
+	 */
+	kasan_unpoison_shadow(objp, size);
+	return size;
+}
+EXPORT_SYMBOL(ksize);
+
 /* Tracepoints definitions. */
 EXPORT_TRACEPOINT_SYMBOL(kmalloc);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc);
diff --git a/mm/slob.c b/mm/slob.c
index 84aefd9b91ee..7f421d0ca9ab 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -527,7 +527,7 @@ void kfree(const void *block)
 EXPORT_SYMBOL(kfree);
 
 /* can't use ksize for kmem_cache_alloc memory, only kmalloc */
-size_t ksize(const void *block)
+size_t __ksize(const void *block)
 {
 	struct page *sp;
 	int align;
@@ -545,7 +545,7 @@ size_t ksize(const void *block)
 	m = (unsigned int *)(block - align);
 	return SLOB_UNITS(*m) * SLOB_UNIT;
 }
-EXPORT_SYMBOL(ksize);
+EXPORT_SYMBOL(__ksize);
 
 int __kmem_cache_create(struct kmem_cache *c, slab_flags_t flags)
 {
diff --git a/mm/slub.c b/mm/slub.c
index cd04dbd2b5d0..05a8d17dd9b2 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3901,7 +3901,7 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 }
 #endif /* CONFIG_HARDENED_USERCOPY */
 
-static size_t __ksize(const void *object)
+size_t __ksize(const void *object)
 {
 	struct page *page;
 
@@ -3917,17 +3917,7 @@ static size_t __ksize(const void *object)
 
 	return slab_ksize(page->slab_cache);
 }
-
-size_t ksize(const void *object)
-{
-	size_t size = __ksize(object);
-	/* We assume that ksize callers could use whole allocated area,
-	 * so we need to unpoison this area.
-	 */
-	kasan_unpoison_shadow(object, size);
-	return size;
-}
-EXPORT_SYMBOL(ksize);
+EXPORT_SYMBOL(__ksize);
 
 void kfree(const void *x)
 {
-- 
2.22.0.410.gd8fdbe21b5-goog

Re: [PATCH v5 4/5] mm/slab: Refactor common ksize KASAN logic into slab_common.c

[Christopher Lameter]

On Mon, 8 Jul 2019, Marco Elver wrote:

> This refactors common code of ksize() between the various allocators
> into slab_common.c: __ksize() is the allocator-specific implementation
> without instrumentation, whereas ksize() includes the required KASAN
> logic.

Acked-by: Christoph Lameter <cl@linux.com>

[PATCH v5 5/5] mm/kasan: Add object validation in ksize()

[Marco Elver]

ksize() has been unconditionally unpoisoning the whole shadow memory region
associated with an allocation. This can lead to various undetected bugs,
for example, double-kzfree().

Specifically, kzfree() uses ksize() to determine the actual allocation
size, and subsequently zeroes the memory. Since ksize() used to just
unpoison the whole shadow memory region, no invalid free was detected.

This patch addresses this as follows:

1. Add a check in ksize(), and only then unpoison the memory region.

2. Preserve kasan_unpoison_slab() semantics by explicitly unpoisoning
   the shadow memory region using the size obtained from __ksize().

Tested:
1. With SLAB allocator: a) normal boot without warnings; b) verified the
   added double-kzfree() is detected.
2. With SLUB allocator: a) normal boot without warnings; b) verified the
   added double-kzfree() is detected.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199359
Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: kasan-dev@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
v4:
* Prefer WARN_ON_ONCE() instead of BUG_ON().
---
 include/linux/kasan.h |  7 +++++--
 mm/slab_common.c      | 22 +++++++++++++++++++++-
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index b40ea104dd36..cc8a03cc9674 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -76,8 +76,11 @@ void kasan_free_shadow(const struct vm_struct *vm);
 int kasan_add_zero_shadow(void *start, unsigned long size);
 void kasan_remove_zero_shadow(void *start, unsigned long size);
 
-size_t ksize(const void *);
-static inline void kasan_unpoison_slab(const void *ptr) { ksize(ptr); }
+size_t __ksize(const void *);
+static inline void kasan_unpoison_slab(const void *ptr)
+{
+	kasan_unpoison_shadow(ptr, __ksize(ptr));
+}
 size_t kasan_metadata_size(struct kmem_cache *cache);
 
 bool kasan_save_enable_multi_shot(void);
diff --git a/mm/slab_common.c b/mm/slab_common.c
index b7c6a40e436a..a09bb10aa026 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1613,7 +1613,27 @@ EXPORT_SYMBOL(kzfree);
  */
 size_t ksize(const void *objp)
 {
-	size_t size = __ksize(objp);
+	size_t size;
+
+	if (WARN_ON_ONCE(!objp))
+		return 0;
+	/*
+	 * We need to check that the pointed to object is valid, and only then
+	 * unpoison the shadow memory below. We use __kasan_check_read(), to
+	 * generate a more useful report at the time ksize() is called (rather
+	 * than later where behaviour is undefined due to potential
+	 * use-after-free or double-free).
+	 *
+	 * If the pointed to memory is invalid we return 0, to avoid users of
+	 * ksize() writing to and potentially corrupting the memory region.
+	 *
+	 * We want to perform the check before __ksize(), to avoid potentially
+	 * crashing in __ksize() due to accessing invalid metadata.
+	 */
+	if (unlikely(objp == ZERO_SIZE_PTR) || !__kasan_check_read(objp, 1))
+		return 0;
+
+	size = __ksize(objp);
 	/*
 	 * We assume that ksize callers could use whole allocated area,
 	 * so we need to unpoison this area.
-- 
2.22.0.410.gd8fdbe21b5-goog

Re: [PATCH v5 0/5] Add object validation in ksize()

[Andrey Ryabinin]

On 7/8/19 8:07 PM, Marco Elver wrote:
> This version fixes several build issues --
> Reported-by: kbuild test robot <lkp@intel.com>
> 
> Previous version here:
> http://lkml.kernel.org/r/20190627094445.216365-1-elver@google.com
> 
> Marco Elver (5):
>   mm/kasan: Introduce __kasan_check_{read,write}
>   mm/kasan: Change kasan_check_{read,write} to return boolean
>   lib/test_kasan: Add test for double-kzfree detection
>   mm/slab: Refactor common ksize KASAN logic into slab_common.c
>   mm/kasan: Add object validation in ksize()
> 

Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>