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Subject: [PATCH] mm, debug, kasan: save and dump freeing stack trace for kasan
To:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Walter Wu <walter-zh.wu@mediatek.com>
Cc:     Qian Cai <cai@lca.pw>, Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        Arnd Bergmann <arnd@arndb.de>, linux-kernel@vger.kernel.org,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com
References: <20190911083921.4158-1-walter-zh.wu@mediatek.com>
 <5E358F4B-552C-4542-9655-E01C7B754F14@lca.pw>
 <c4d2518f-4813-c941-6f47-73897f420517@suse.cz>
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 <613f9f23-c7f0-871f-fe13-930c35ef3105@suse.cz>
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 <6d58ce86-b2a4-40af-bf40-c604b457d086@suse.cz>
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From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <d98bf550-367d-0744-025a-52307248ec82@suse.cz>
Date:   Mon, 23 Sep 2019 10:20:59 +0200
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On 9/16/19 5:57 PM, Andrey Ryabinin wrote:
> I'd rather keep all logic in one place, i.e. "if (!page_owner_disabled && (IS_ENABLED(CONFIG_KASAN) || debug_pagealloc_enabled())"
> With this no changes in early_debug_pagealloc() required and CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT=y should also work correctly.

OK.

----8<----

From 7437c43f02682fdde5680fa83e87029f7529e222 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@suse.cz>
Date: Mon, 16 Sep 2019 11:28:19 +0200
Subject: [PATCH] mm, debug, kasan: save and dump freeing stack trace for kasan

The commit "mm, page_owner, debug_pagealloc: save and dump freeing stack trace"
enhanced page_owner to also store freeing stack trace, when debug_pagealloc is
also enabled. KASAN would also like to do this [1] to improve error reports to
debug e.g. UAF issues. This patch therefore introduces a helper config option
PAGE_OWNER_FREE_STACK, which is enabled when PAGE_OWNER and either of
DEBUG_PAGEALLOC or KASAN is enabled. Boot-time, the free stack saving is
enabled when booting a KASAN kernel with page_owner=on, or non-KASAN kernel
with debug_pagealloc=on and page_owner=on.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=203967

Suggested-by: Dmitry Vyukov <dvyukov@google.com>
Suggested-by: Walter Wu <walter-zh.wu@mediatek.com>
Suggested-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 Documentation/dev-tools/kasan.rst |  4 ++++
 mm/Kconfig.debug                  |  4 ++++
 mm/page_owner.c                   | 31 ++++++++++++++++++-------------
 3 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index b72d07d70239..434e605030e9 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -41,6 +41,10 @@ smaller binary while the latter is 1.1 - 2 times faster.
 Both KASAN modes work with both SLUB and SLAB memory allocators.
 For better bug detection and nicer reporting, enable CONFIG_STACKTRACE.
 
+To augment reports with last allocation and freeing stack of the physical
+page, it is recommended to configure kernel also with CONFIG_PAGE_OWNER = y
+and boot with page_owner=on.
+
 To disable instrumentation for specific files or directories, add a line
 similar to the following to the respective kernel Makefile:
 
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 327b3ebf23bf..1ea247da3322 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -62,6 +62,10 @@ config PAGE_OWNER
 
 	  If unsure, say N.
 
+config PAGE_OWNER_FREE_STACK
+	def_bool KASAN || DEBUG_PAGEALLOC
+	depends on PAGE_OWNER
+
 config PAGE_POISONING
 	bool "Poison pages after freeing"
 	select PAGE_POISONING_NO_SANITY if HIBERNATION
diff --git a/mm/page_owner.c b/mm/page_owner.c
index dee931184788..8b6b05676158 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -24,13 +24,14 @@ struct page_owner {
 	short last_migrate_reason;
 	gfp_t gfp_mask;
 	depot_stack_handle_t handle;
-#ifdef CONFIG_DEBUG_PAGEALLOC
+#ifdef CONFIG_PAGE_OWNER_FREE_STACK
 	depot_stack_handle_t free_handle;
 #endif
 };
 
 static bool page_owner_disabled = true;
 DEFINE_STATIC_KEY_FALSE(page_owner_inited);
+static DEFINE_STATIC_KEY_FALSE(page_owner_free_stack);
 
 static depot_stack_handle_t dummy_handle;
 static depot_stack_handle_t failure_handle;
@@ -91,6 +92,8 @@ static void init_page_owner(void)
 	register_failure_stack();
 	register_early_stack();
 	static_branch_enable(&page_owner_inited);
+	if (IS_ENABLED(CONFIG_KASAN) || debug_pagealloc_enabled())
+		static_branch_enable(&page_owner_free_stack);
 	init_early_allocated_pages();
 }
 
@@ -148,11 +151,11 @@ void __reset_page_owner(struct page *page, unsigned int order)
 {
 	int i;
 	struct page_ext *page_ext;
-#ifdef CONFIG_DEBUG_PAGEALLOC
+#ifdef CONFIG_PAGE_OWNER_FREE_STACK
 	depot_stack_handle_t handle = 0;
 	struct page_owner *page_owner;
 
-	if (debug_pagealloc_enabled())
+	if (static_branch_unlikely(&page_owner_free_stack))
 		handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
 #endif
 
@@ -161,8 +164,8 @@ void __reset_page_owner(struct page *page, unsigned int order)
 		if (unlikely(!page_ext))
 			continue;
 		__clear_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags);
-#ifdef CONFIG_DEBUG_PAGEALLOC
-		if (debug_pagealloc_enabled()) {
+#ifdef CONFIG_PAGE_OWNER_FREE_STACK
+		if (static_branch_unlikely(&page_owner_free_stack)) {
 			page_owner = get_page_owner(page_ext);
 			page_owner->free_handle = handle;
 		}
@@ -451,14 +454,16 @@ void __dump_page_owner(struct page *page)
 		stack_trace_print(entries, nr_entries, 0);
 	}
 
-#ifdef CONFIG_DEBUG_PAGEALLOC
-	handle = READ_ONCE(page_owner->free_handle);
-	if (!handle) {
-		pr_alert("page_owner free stack trace missing\n");
-	} else {
-		nr_entries = stack_depot_fetch(handle, &entries);
-		pr_alert("page last free stack trace:\n");
-		stack_trace_print(entries, nr_entries, 0);
+#ifdef CONFIG_PAGE_OWNER_FREE_STACK
+	if (static_branch_unlikely(&page_owner_free_stack)) {
+		handle = READ_ONCE(page_owner->free_handle);
+		if (!handle) {
+			pr_alert("page_owner free stack trace missing\n");
+		} else {
+			nr_entries = stack_depot_fetch(handle, &entries);
+			pr_alert("page last free stack trace:\n");
+			stack_trace_print(entries, nr_entries, 0);
+		}
 	}
 #endif
 
-- 
2.23.0