[PATCH v8 14/15] mm/kasan: Introduce helpers for lazy MMU mode sanitizer

[Alexander Gordeev <agordeev@linux.ibm.com>]

Provide helpers that allow architectures implement
illegitimate PTE direct accesses while the lazy MMU
mode is enabled, such as:

	pte_t pte = *ptep;
	*ptep = pte;

By contrast, these would have to be:

	pte_t pte = ptep_get(ptep);
	set_pte(ptep, pte);

The direct PTE accesses pose a real issue on s390.

Suggested-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
---
 include/linux/kasan.h     | 19 +++++++++++++++++--
 mm/kasan/common.c         | 14 ++++++++++++++
 mm/kasan/kasan.h          |  2 ++
 mm/kasan/report_generic.c |  3 +++
 4 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index ff41949c0ac0..01f710f03114 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -6,6 +6,7 @@
 #include <linux/kasan-enabled.h>
 #include <linux/kasan-tags.h>
 #include <linux/kernel.h>
+#include <linux/pgtable.h>
 #include <linux/static_key.h>
 #include <linux/types.h>
 
@@ -35,8 +36,6 @@ typedef unsigned int __bitwise kasan_vmalloc_flags_t;
 
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 
-#include <linux/pgtable.h>
-
 /* Software KASAN implementations use shadow memory. */
 
 #ifdef CONFIG_KASAN_SW_TAGS
@@ -134,6 +133,20 @@ static __always_inline void kasan_poison_slab(struct slab *slab)
 		__kasan_poison_slab(slab);
 }
 
+void __kasan_poison_pte(hw_pte_t *pte, int nr);
+static __always_inline void kasan_poison_pte(hw_pte_t *pte, int nr)
+{
+	if (kasan_enabled())
+		__kasan_poison_pte(pte, nr);
+}
+
+void __kasan_unpoison_pte(hw_pte_t *pte, int nr);
+static __always_inline void kasan_unpoison_pte(hw_pte_t *pte, int nr)
+{
+	if (kasan_enabled())
+		__kasan_unpoison_pte(pte, nr);
+}
+
 void __kasan_unpoison_new_object(struct kmem_cache *cache, void *object);
 /**
  * kasan_unpoison_new_object - Temporarily unpoison a new slab object.
@@ -414,6 +427,8 @@ static inline bool kasan_unpoison_pages(struct page *page, unsigned int order,
 	return false;
 }
 static inline void kasan_poison_slab(struct slab *slab) {}
+static inline void kasan_poison_pte(hw_pte_t *pte, int nr) {}
+static inline void kasan_unpoison_pte(hw_pte_t *pte, int nr) {}
 static inline void kasan_unpoison_new_object(struct kmem_cache *cache,
 					void *object) {}
 static inline void kasan_poison_new_object(struct kmem_cache *cache,
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 7d21c4db68d2..f3cbbeb8ad0e 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -174,6 +174,20 @@ void __kasan_poison_slab(struct slab *slab)
 		     KASAN_SLAB_REDZONE, false);
 }
 
+void __kasan_poison_pte(hw_pte_t *pte, int nr)
+{
+	if (IS_ALIGNED(sizeof(*pte), KASAN_GRANULE_SIZE))
+		kasan_poison(pte, sizeof(*pte) * nr, KASAN_LAZY_MMU_PTE, false);
+}
+EXPORT_SYMBOL_GPL(__kasan_poison_pte);
+
+void __kasan_unpoison_pte(hw_pte_t *pte, int nr)
+{
+	if (IS_ALIGNED(sizeof(*pte), KASAN_GRANULE_SIZE))
+		kasan_unpoison(pte, sizeof(*pte) * nr, false);
+}
+EXPORT_SYMBOL_GPL(__kasan_unpoison_pte);
+
 void __kasan_unpoison_new_object(struct kmem_cache *cache, void *object)
 {
 	kasan_unpoison(object, cache->object_size, false);
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index fc9169a54766..1a2d18cdb21d 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -144,12 +144,14 @@ static inline bool kasan_requires_meta(void)
 #define KASAN_PAGE_REDZONE	0xFE  /* redzone for kmalloc_large allocation */
 #define KASAN_SLAB_REDZONE	0xFC  /* redzone for slab object */
 #define KASAN_SLAB_FREE		0xFB  /* freed slab object */
+#define KASAN_LAZY_MMU_PTE	0xFD  /* direct pte access in lazy mmu mode */
 #define KASAN_VMALLOC_INVALID	0xF8  /* inaccessible space in vmap area */
 #else
 #define KASAN_PAGE_FREE		KASAN_TAG_INVALID
 #define KASAN_PAGE_REDZONE	KASAN_TAG_INVALID
 #define KASAN_SLAB_REDZONE	KASAN_TAG_INVALID
 #define KASAN_SLAB_FREE		KASAN_TAG_INVALID
+#define KASAN_LAZY_MMU_PTE	KASAN_TAG_INVALID
 #define KASAN_VMALLOC_INVALID	KASAN_TAG_INVALID /* only used for SW_TAGS */
 #endif
 
diff --git a/mm/kasan/report_generic.c b/mm/kasan/report_generic.c
index f5b8e37b3805..489d4a8d6902 100644
--- a/mm/kasan/report_generic.c
+++ b/mm/kasan/report_generic.c
@@ -113,6 +113,9 @@ static const char *get_shadow_bug_type(struct kasan_report_info *info)
 	case KASAN_SLAB_FREE_META:
 		bug_type = "slab-use-after-free";
 		break;
+	case KASAN_LAZY_MMU_PTE:
+		bug_type = "lazy-mmu-pte-access";
+		break;
 	case KASAN_ALLOCA_LEFT:
 	case KASAN_ALLOCA_RIGHT:
 		bug_type = "alloca-out-of-bounds";
-- 
2.53.0