Commit 0fe9a448 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
Browse files

mm, page_owner: decouple freeing stack trace from debug_pagealloc 

Commit 8974558f ("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.

Kirill has suggested that the freeing stack trace saving should be also
possible to be enabled separately from KASAN or debug_pagealloc, i.e.
with an extra boot option.  Qian argued that we have enough options
already, and avoiding the extra overhead is not worth the complications
in the case of a debugging option.  Kirill noted that the extra stack
handle in struct page_owner requires 0.1% of memory.

This patch therefore enables free stack saving whenever page_owner is
enabled, regardless of whether debug_pagealloc or KASAN is also enabled.
KASAN kernels booted with page_owner=on will thus benefit from the
improved error reports.

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

[vbabka@suse.cz: v3]
  Link: http://lkml.kernel.org/r/20191007091808.7096-3-vbabka@suse.cz
Link: http://lkml.kernel.org/r/20190930122916.14969-3-vbabka@suse.cz


Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarQian Cai <cai@lca.pw>
Suggested-by: default avatarDmitry Vyukov <dvyukov@google.com>
Suggested-by: default avatarWalter Wu <walter-zh.wu@mediatek.com>
Suggested-by: default avatarAndrey Ryabinin <aryabinin@virtuozzo.com>
Suggested-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Suggested-by: default avatarQian Cai <cai@lca.pw>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5556cfe8

Documentation/dev-tools/kasan.rst

+3 −0
Original line number Diff line number Diff line
@@ -41,6 +41,9 @@ 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 enable also CONFIG_PAGE_OWNER 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:

mm/page_owner.c

+7 −21
Original line number Diff line number Diff line
@@ -24,12 +24,10 @@ struct page_owner { 
	short last_migrate_reason;

	gfp_t gfp_mask;

	depot_stack_handle_t handle;

#ifdef CONFIG_DEBUG_PAGEALLOC

	depot_stack_handle_t free_handle;

#endif

};



static bool page_owner_disabled = true;

static bool page_owner_enabled = false;

DEFINE_STATIC_KEY_FALSE(page_owner_inited);



static depot_stack_handle_t dummy_handle;
@@ -44,7 +42,7 @@ static int __init early_page_owner_param(char *buf) 
		return -EINVAL;



	if (strcmp(buf, "on") == 0)

		page_owner_disabled = false;

		page_owner_enabled = true;



	return 0;

}
@@ -52,10 +50,7 @@ early_param("page_owner", early_page_owner_param); 


static bool need_page_owner(void)

{

	if (page_owner_disabled)

		return false;



	return true;

	return page_owner_enabled;

}



static __always_inline depot_stack_handle_t create_dummy_stack(void)
@@ -84,7 +79,7 @@ static noinline void register_early_stack(void) 


static void init_page_owner(void)

{

	if (page_owner_disabled)

	if (!page_owner_enabled)

		return;



	register_dummy_stack();
@@ -148,25 +143,18 @@ void __reset_page_owner(struct page *page, unsigned int order) 
{

	int i;

	struct page_ext *page_ext;

#ifdef CONFIG_DEBUG_PAGEALLOC

	depot_stack_handle_t handle = 0;

	struct page_owner *page_owner;



	if (debug_pagealloc_enabled())

	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);

#endif



	page_ext = lookup_page_ext(page);

	if (unlikely(!page_ext))

		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()) {

		page_owner = get_page_owner(page_ext);

		page_owner->free_handle = handle;

		}

#endif

		page_ext = page_ext_next(page_ext);

	}

}
@@ -450,7 +438,6 @@ 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");
@@ -459,7 +446,6 @@ void __dump_page_owner(struct page *page) 
		pr_alert("page last free stack trace:\n");

		stack_trace_print(entries, nr_entries, 0);

	}

#endif



	if (page_owner->last_migrate_reason != -1)

		pr_alert("page has been migrated, last migrate reason: %s\n",

CRA Git | Maintained and supported by SUSTech CRA and CCSE