[PATCH v6 03/39] kasan, page_alloc: merge kasan_free_pages into free_pages_prepare

andrey.konovalov
2022-01-24T18:32:20Z

Currently, the code responsible for initializing and poisoning memory
in free_pages_prepare() is scattered across two locations:
kasan_free_pages() for HW_TAGS KASAN and free_pages_prepare() itself.
This is confusing.

This and a few following patches combine the code from these two
locations. Along the way, these patches also simplify the performed
checks to make them easier to follow.

Replaces the only caller of kasan_free_pages() with its implementation.

As kasan_has_integrated_init() is only true when CONFIG_KASAN_HW_TAGS
is enabled, moving the code does no functional changes.

This patch is not useful by itself but makes the simplifications in
the following patches easier to follow.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>

---

Changes v2->v3:
- Update patch description.
---
include/linux/kasan.h | 8 --------
mm/kasan/common.c | 2 +-
mm/kasan/hw_tags.c | 11 -----------
mm/page_alloc.c | 6 ++++--
4 files changed, 5 insertions(+), 22 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 4a45562d8893..a8bfe9f157c9 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -96,7 +96,6 @@ static inline bool kasan_hw_tags_enabled(void)
}

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 */

@@ -117,13 +116,6 @@ static __always_inline void kasan_alloc_pages(struct page *page,
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 */

static inline bool kasan_has_integrated_init(void)
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 92196562687b..a0082fad48b1 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -387,7 +387,7 @@ static inline bool ____kasan_kfree_large(void *ptr, unsigned long ip)
}

/*
- * The object will be poisoned by kasan_free_pages() or
+ * The object will be poisoned by kasan_poison_pages() or
* kasan_slab_free_mempool().
*/

diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 7355cb534e4f..0b8225add2e4 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -213,17 +213,6 @@ void kasan_alloc_pages(struct page *page, unsigned int order, gfp_t flags)
}
}

-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_enable_tagging_sync(void)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 012170b1c47a..e5f95c6ab0ac 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1368,15 +1368,17 @@ static __always_inline bool free_pages_prepare(struct page *page,

/*
* As memory initialization might be integrated into KASAN,
- * kasan_free_pages and kernel_init_free_pages must be
+ * KASAN poisoning and memory initialization code must be
* kept together to avoid discrepancies in behavior.
*
* With hardware tag-based KASAN, memory tags must be set before the
* page becomes unavailable via debug_pagealloc or arch_free_page.
*/
if (kasan_has_integrated_init()) {
+ bool init = want_init_on_free();
+
if (!skip_kasan_poison)
- kasan_free_pages(page, order);
+ kasan_poison_pages(page, order, init);
} else {
bool init = want_init_on_free();