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Date:   Fri, 26 Feb 2021 02:25:37 +0100
Message-Id: <1aa83e48627978de8068d5e3314185f3a0d7a849.1614302398.git.andreyknvl@google.com>
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Subject: [PATCH] kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC
From:   Andrey Konovalov <andreyknvl@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Christoph Hellwig <hch@infradead.org>,
        kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Currently, kasan_free_nondeferred_pages()->kasan_free_pages() is called
after debug_pagealloc_unmap_pages(). This causes a crash when
debug_pagealloc is enabled, as HW_TAGS KASAN can't set tags on an
unmapped page.

This patch puts kasan_free_nondeferred_pages() before
debug_pagealloc_unmap_pages().

Besides fixing the crash, this also makes the annotation order consistent
with debug_pagealloc_map_pages() preceding kasan_alloc_pages().

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/page_alloc.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c89e7b107514..54bc237fd319 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1311,10 +1311,14 @@ static __always_inline bool free_pages_prepare(struct page *page,
 	 */
 	arch_free_page(page, order);
 
-	debug_pagealloc_unmap_pages(page, 1 << order);
-
+	/*
+	 * With hardware tag-based KASAN, memory tags must be set
+	 * before unmapping the page with debug_pagealloc.
+	 */
 	kasan_free_nondeferred_pages(page, order, fpi_flags);
 
+	debug_pagealloc_unmap_pages(page, 1 << order);
+
 	return true;
 }
 
-- 
2.30.1.766.gb4fecdf3b7-goog