Re: [PATCH 2/3] mm, debug, kasan: save and dump freeing stack trace for kasan

[Kirill A. Shutemov]

On Wed, Sep 25, 2019 at 04:30:51PM +0200, Vlastimil Babka wrote:
> The commit 8974558f49a6 ("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.

I would like to have an option to enable free stack for any PAGE_OWNER
user at boot-time.

Maybe drop CONFIG_PAGE_OWNER_FREE_STACK completely and add
page_owner_free=on cmdline option as yet another way to trigger
'static_branch_enable(&page_owner_free_stack)'?

> [1] https://bugzilla.kernel.org/show_bug.cgi?id=203967
> 
> Suggested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Suggested-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
> Suggested-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> ---
>  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

Nit: remove spaces around '=' or write "with CONFIG_PAGE_OWNER enabled".

> +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 d3cf5d336ccf..f3aeec78822f 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)
>  		return;
>  	for (i = 0; i < (1 << order); i++) {
>  		__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;
>  		}
> @@ -450,14 +453,16 @@ 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
> 
> 

-- 
 Kirill A. Shutemov