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SubjectRe: [PATCH 2/3] mm, debug, kasan: save and dump freeing stack trace for kasan
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@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>
> Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> ---
> 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

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