[PATCH AUTOSEL 5.18 09/53] mm: kasan: Skip unpoisoning of user pages

[Sasha Levin]

From: Catalin Marinas <catalin.marinas at arm.com>

[ Upstream commit 70c248aca9e7efa85a6664d5ab56c17c326c958f ]

Commit c275c5c6d50a ("kasan: disable freed user page poisoning with HW
tags") added __GFP_SKIP_KASAN_POISON to GFP_HIGHUSER_MOVABLE. A similar
argument can be made about unpoisoning, so also add
__GFP_SKIP_KASAN_UNPOISON to user pages. To ensure the user page is
still accessible via page_address() without a kasan fault, reset the
page->flags tag.

With the above changes, there is no need for the arm64
tag_clear_highpage() to reset the page->flags tag.

Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Cc: Andrey Ryabinin <ryabinin.a.a at gmail.com>
Cc: Andrey Konovalov <andreyknvl at gmail.com>
Cc: Peter Collingbourne <pcc at google.com>
Cc: Vincenzo Frascino <vincenzo.frascino at arm.com>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino at arm.com>
Reviewed-by: Andrey Konovalov <andreyknvl at gmail.com>
Link: https://lore.kernel.org/r/20220610152141.2148929-3-catalin.marinas@arm.com
Signed-off-by: Will Deacon <will at kernel.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 arch/arm64/mm/fault.c | 1 -
 include/linux/gfp.h   | 2 +-
 mm/page_alloc.c       | 7 +++++--
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 77341b160aca..f2f21cd6d43f 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -926,6 +926,5 @@ struct page *alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma,
 void tag_clear_highpage(struct page *page)
 {
 	mte_zero_clear_page_tags(page_address(page));
-	page_kasan_tag_reset(page);
 	set_bit(PG_mte_tagged, &page->flags);
 }
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 3e3d36fc2109..df0ec30524fb 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -348,7 +348,7 @@ struct vm_area_struct;
 #define GFP_DMA32	__GFP_DMA32
 #define GFP_HIGHUSER	(GFP_USER | __GFP_HIGHMEM)
 #define GFP_HIGHUSER_MOVABLE	(GFP_HIGHUSER | __GFP_MOVABLE | \
-			 __GFP_SKIP_KASAN_POISON)
+			 __GFP_SKIP_KASAN_POISON | __GFP_SKIP_KASAN_UNPOISON)
 #define GFP_TRANSHUGE_LIGHT	((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
 			 __GFP_NOMEMALLOC | __GFP_NOWARN) & ~__GFP_RECLAIM)
 #define GFP_TRANSHUGE	(GFP_TRANSHUGE_LIGHT | __GFP_DIRECT_RECLAIM)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5ced6cb260ed..edef84efba76 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2382,6 +2382,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 	bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) &&
 			!should_skip_init(gfp_flags);
 	bool init_tags = init && (gfp_flags & __GFP_ZEROTAGS);
+	int i;
 
 	set_page_private(page, 0);
 	set_page_refcounted(page);
@@ -2407,8 +2408,6 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 	 * should be initialized as well).
 	 */
 	if (init_tags) {
-		int i;
-
 		/* Initialize both memory and tags. */
 		for (i = 0; i != 1 << order; ++i)
 			tag_clear_highpage(page + i);
@@ -2423,6 +2422,10 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 		/* Note that memory is already initialized by KASAN. */
 		if (kasan_has_integrated_init())
 			init = false;
+	} else {
+		/* Ensure page_address() dereferencing does not fault. */
+		for (i = 0; i != 1 << order; ++i)
+			page_kasan_tag_reset(page + i);
 	}
 	/* If memory is still not initialized, do it now. */
 	if (init)
-- 
2.35.1