Subject: [PATCH v6 2/4] kasan: use separate (un)poison implementation for integrated init

From: Peter Collingbourne <[email-masked]>
Date: Wed, 2 Jun 2021 16:52:28 -0700

Currently with integrated init page_alloc.c needs to know whether
kasan_alloc_pages() will zero initialize memory, but this will start
becoming more complicated once we start adding tag initialization
support for user pages. To avoid page_alloc.c needing to know more
details of what integrated init will do, move the unpoisoning logic
for integrated init into the HW tags implementation. Currently the
logic is identical but it will diverge in subsequent patches.

For symmetry do the same for poisoning although this logic will
be unaffected by subsequent patches.

Signed-off-by: Peter Collingbourne <[email-masked]>
Reviewed-by: Andrey Konovalov <[email-masked]>
Link: https://linux-review.googlesource.com/id/I2c550234c6c4a893c48c18ff0c6ce658c7c67056
---
v4:
- use IS_ENABLED(CONFIG_KASAN)
- add comments to kasan_alloc_pages and kasan_free_pages
- remove line break

v3:
- use BUILD_BUG()

v2:
- fix build with KASAN disabled

 include/linux/kasan.h | 64 +++++++++++++++++++++++++------------------
 mm/kasan/common.c     |  4 +--
 mm/kasan/hw_tags.c    | 22 +++++++++++++++
 mm/mempool.c          |  6 ++--
 mm/page_alloc.c       | 55 +++++++++++++++++++------------------
 5 files changed, 95 insertions(+), 56 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index b1678a61e6a7..a1c7ce5f3e4f 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_KASAN_H
 #define _LINUX_KASAN_H
 
+#include <linux/bug.h>
 #include <linux/static_key.h>
 #include <linux/types.h>
 
@@ -79,14 +80,6 @@ static inline void kasan_disable_current(void) {}
 
 #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
 
-#ifdef CONFIG_KASAN
-
-struct kasan_cache {
-	int alloc_meta_offset;
-	int free_meta_offset;
-	bool is_kmalloc;
-};
-
 #ifdef CONFIG_KASAN_HW_TAGS
 
 DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
@@ -101,11 +94,14 @@ static inline bool kasan_has_integrated_init(void)
 	return kasan_enabled();
 }
 
+void kasan_alloc_pages(struct page *page, unsigned int order, gfp_t flags);
+void kasan_free_pages(struct page *page, unsigned int order);
+
 #else /* CONFIG_KASAN_HW_TAGS */
 
 static inline bool kasan_enabled(void)
 {
-	return true;
+	return IS_ENABLED(CONFIG_KASAN);
 }
 
 static inline bool kasan_has_integrated_init(void)
@@ -113,8 +109,30 @@ static inline bool kasan_has_integrated_init(void)
 	return false;
 }
 
+static __always_inline void kasan_alloc_pages(struct page *page,
+					      unsigned int order, gfp_t flags)
+{
+	/* Only available for integrated init. */
+	BUILD_BUG();
+}
+
+static __always_inline void kasan_free_pages(struct page *page,
+					     unsigned int order)
+{
+	/* Only available for integrated init. */
+	BUILD_BUG();
+}
+
 #endif /* CONFIG_KASAN_HW_TAGS */
 
+#ifdef CONFIG_KASAN
+
+struct kasan_cache {
+	int alloc_meta_offset;
+	int free_meta_offset;
+	bool is_kmalloc;
+};
+
 slab_flags_t __kasan_never_merge(void);
 static __always_inline slab_flags_t kasan_never_merge(void)
 {
@@ -130,20 +148,20 @@ static __always_inline void kasan_unpoison_range(const void *addr, size_t size)
 		__kasan_unpoison_range(addr, size);
 }
 
-void __kasan_alloc_pages(struct page *page, unsigned int order, bool init);
-static __always_inline void kasan_alloc_pages(struct page *page,
+void __kasan_poison_pages(struct page *page, unsigned int order, bool init);
+static __always_inline void kasan_poison_pages(struct page *page,
 						unsigned int order, bool init)
 {
 	if (kasan_enabled())
-		__kasan_alloc_pages(page, order, init);
+		__kasan_poison_pages(page, order, init);
 }
 
-void __kasan_free_pages(struct page *page, unsigned int order, bool init);
-static __always_inline void kasan_free_pages(struct page *page,
-						unsigned int order, bool init)
+void __kasan_unpoison_pages(struct page *page, unsigned int order, bool init);
+static __always_inline void kasan_unpoison_pages(struct page *page,
+						 unsigned int order, bool init)
 {
 	if (kasan_enabled())
-		__kasan_free_pages(page, order, init);
+		__kasan_unpoison_pages(page, order, init);
 }
 
 void __kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
@@ -285,21 +303,15 @@ void kasan_restore_multi_shot(bool enabled);
 
 #else /* CONFIG_KASAN */
 
-static inline bool kasan_enabled(void)
-{
-	return false;
-}
-static inline bool kasan_has_integrated_init(void)
-{
-	return false;
-}
 static inline slab_flags_t kasan_never_merge(void)
 {
 	return 0;
 }
 static inline void kasan_unpoison_range(const void *address, size_t size) {}
-static inline void kasan_alloc_pages(struct page *page, unsigned int order, bool init) {}
-static inline void kasan_free_pages(struct page *page, unsigned int order, bool init) {}
+static inline void kasan_poison_pages(struct page *page, unsigned int order,
+				      bool init) {}
+static inline void kasan_unpoison_pages(struct page *page, unsigned int order,
+					bool init) {}
 static inline void kasan_cache_create(struct kmem_cache *cache,
 				      unsigned int *size,
 				      slab_flags_t *flags) {}
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 6bb87f2acd4e..0ecd293af344 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -97,7 +97,7 @@ slab_flags_t __kasan_never_merge(void)
 	return 0;
 }
 
-void __kasan_alloc_pages(struct page *page, unsigned int order, bool init)
+void __kasan_unpoison_pages(struct page *page, unsigned int order, bool init)
 {
 	u8 tag;
 	unsigned long i;
@@ -111,7 +111,7 @@ void __kasan_alloc_pages(struct page *page, unsigned int order, bool init)
 	kasan_unpoison(page_address(page), PAGE_SIZE << order, init);
 }
 
-void __kasan_free_pages(struct page *page, unsigned int order, bool init)
+void __kasan_poison_pages(struct page *page, unsigned int order, bool init)
 {
 	if (likely(!PageHighMem(page)))
 		kasan_poison(page_address(page), PAGE_SIZE << order,
diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 4004388b4e4b..9d0f6f934016 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -238,6 +238,28 @@ struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
 	return &alloc_meta->free_track[0];
 }
 
+void kasan_alloc_pages(struct page *page, unsigned int order, gfp_t flags)
+{
+	/*
+	 * This condition should match the one in post_alloc_hook() in
+	 * page_alloc.c.
+	 */
+	bool init = !want_init_on_free() && want_init_on_alloc(flags);
+
+	kasan_unpoison_pages(page, order, init);
+}
+
+void kasan_free_pages(struct page *page, unsigned int order)
+{
+	/*
+	 * This condition should match the one in free_pages_prepare() in
+	 * page_alloc.c.
+	 */
+	bool init = want_init_on_free();
+
+	kasan_poison_pages(page, order, init);
+}
+
 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
 
 void kasan_set_tagging_report_once(bool state)
diff --git a/mm/mempool.c b/mm/mempool.c
index a258cf4de575..0b8afbec3e35 100644
--- a/mm/mempool.c
+++ b/mm/mempool.c
@@ -106,7 +106,8 @@ static __always_inline void kasan_poison_element(mempool_t *pool, void *element)
 	if (pool->alloc == mempool_alloc_slab || pool->alloc == mempool_kmalloc)
 		kasan_slab_free_mempool(element);
 	else if (pool->alloc == mempool_alloc_pages)
-		kasan_free_pages(element, (unsigned long)pool->pool_data, false);
+		kasan_poison_pages(element, (unsigned long)pool->pool_data,
+				   false);
 }
 
 static void kasan_unpoison_element(mempool_t *pool, void *element)
@@ -114,7 +115,8 @@ static void kasan_unpoison_element(mempool_t *pool, void *element)
 	if (pool->alloc == mempool_alloc_slab || pool->alloc == mempool_kmalloc)
 		kasan_unpoison_range(element, __ksize(element));
 	else if (pool->alloc == mempool_alloc_pages)
-		kasan_alloc_pages(element, (unsigned long)pool->pool_data, false);
+		kasan_unpoison_pages(element, (unsigned long)pool->pool_data,
+				     false);
 }
 
 static __always_inline void add_element(mempool_t *pool, void *element)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index aaa1655cf682..4fddb7cac3c6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -382,7 +382,7 @@ int page_group_by_mobility_disabled __read_mostly;
 static DEFINE_STATIC_KEY_TRUE(deferred_pages);
 
 /*
- * Calling kasan_free_pages() only after deferred memory initialization
+ * Calling kasan_poison_pages() only after deferred memory initialization
  * has completed. Poisoning pages during deferred memory init will greatly
  * lengthen the process and cause problem in large memory systems as the
  * deferred pages initialization is done with interrupt disabled.
@@ -394,15 +394,11 @@ static DEFINE_STATIC_KEY_TRUE(deferred_pages);
  * on-demand allocation and then freed again before the deferred pages
  * initialization is done, but this is not likely to happen.
  */
-static inline void kasan_free_nondeferred_pages(struct page *page, int order,
-						bool init, fpi_t fpi_flags)
+static inline bool should_skip_kasan_poison(fpi_t fpi_flags)
 {
-	if (static_branch_unlikely(&deferred_pages))
-		return;
-	if (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
-			(fpi_flags & FPI_SKIP_KASAN_POISON))
-		return;
-	kasan_free_pages(page, order, init);
+	return static_branch_unlikely(&deferred_pages) ||
+	       (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
+		(fpi_flags & FPI_SKIP_KASAN_POISON));
 }
 
 /* Returns true if the struct page for the pfn is uninitialised */
@@ -453,13 +449,10 @@ defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
 	return false;
 }
 #else
-static inline void kasan_free_nondeferred_pages(struct page *page, int order,
-						bool init, fpi_t fpi_flags)
+static inline bool should_skip_kasan_poison(fpi_t fpi_flags)
 {
-	if (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
-			(fpi_flags & FPI_SKIP_KASAN_POISON))
-		return;
-	kasan_free_pages(page, order, init);
+	return (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
+		(fpi_flags & FPI_SKIP_KASAN_POISON));
 }
 
 static inline bool early_page_uninitialised(unsigned long pfn)
@@ -1245,7 +1238,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
 			unsigned int order, bool check_free, fpi_t fpi_flags)
 {
 	int bad = 0;
-	bool init;
+	bool skip_kasan_poison = should_skip_kasan_poison(fpi_flags);
 
 	VM_BUG_ON_PAGE(PageTail(page), page);
 
@@ -1314,10 +1307,17 @@ static __always_inline bool free_pages_prepare(struct page *page,
 	 * With hardware tag-based KASAN, memory tags must be set before the
 	 * page becomes unavailable via debug_pagealloc or arch_free_page.
 	 */
-	init = want_init_on_free();
-	if (init && !kasan_has_integrated_init())
-		kernel_init_free_pages(page, 1 << order);
-	kasan_free_nondeferred_pages(page, order, init, fpi_flags);
+	if (kasan_has_integrated_init()) {
+		if (!skip_kasan_poison)
+			kasan_free_pages(page, order);
+	} else {
+		bool init = want_init_on_free();
+
+		if (init)
+			kernel_init_free_pages(page, 1 << order);
+		if (!skip_kasan_poison)
+			kasan_poison_pages(page, order, init);
+	}
 
 	/*
 	 * arch_free_page() can make the page's contents inaccessible.  s390
@@ -2324,8 +2324,6 @@ static bool check_new_pages(struct page *page, unsigned int order)
 inline void post_alloc_hook(struct page *page, unsigned int order,
 				gfp_t gfp_flags)
 {
-	bool init;
-
 	set_page_private(page, 0);
 	set_page_refcounted(page);
 
@@ -2344,10 +2342,15 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 	 * kasan_alloc_pages and kernel_init_free_pages must be
 	 * kept together to avoid discrepancies in behavior.
 	 */
-	init = !want_init_on_free() && want_init_on_alloc(gfp_flags);
-	kasan_alloc_pages(page, order, init);
-	if (init && !kasan_has_integrated_init())
-		kernel_init_free_pages(page, 1 << order);
+	if (kasan_has_integrated_init()) {
+		kasan_alloc_pages(page, order, gfp_flags);
+	} else {
+		bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags);
+
+		kasan_unpoison_pages(page, order, init);
+		if (init)
+			kernel_init_free_pages(page, 1 << order);
+	}
 
 	set_page_owner(page, order, gfp_flags);
 }
-- 
2.32.0.rc1.229.g3e70b5a671-goog

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