mm: kasan: Skip unpoisoning of user pages

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@arm.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://lore.kernel.org/r/20220610152141.2148929-3-catalin.marinas@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index c5e11768e5c141ae854ef3b71cfbf8a1ca17d907..cdf3ffa0c22340e6bcb91077a4363d74e75ef82f 100644 (file)
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -927,6 +927,5 @@ 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 2d2ccae933c207cc9818679129f37d66f78959c8..0ace7759acd22345908edc19280f451ab015f214 100644 (file)
--- 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 e008a3df0485c79ac24ef31b4407dd5921a9649a..f6ed240870bc2142ff8fad0153a43834eff2e215 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2397,6 +2397,7 @@ 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);
@@ -2422,8 +2423,6 @@ 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);
@@ -2438,6 +2437,10 @@ 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)