From: Vlastimil Babka <vbabka@xxxxxxx>
Subject: mm, page_owner: decouple freeing stack trace from debug_pagealloc
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. 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@xxxxxxx: v3]
Link: http://lkml.kernel.org/r/20191007091808.7096-3-vbabka@xxxxxxx
Link: http://lkml.kernel.org/r/20190930122916.14969-3-vbabka@xxxxxxx
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Reviewed-by: Qian Cai <cai@xxxxxx>
Suggested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Suggested-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
Suggested-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Suggested-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Suggested-by: Qian Cai <cai@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/dev-tools/kasan.rst | 3 +++
mm/page_owner.c | 28 +++++++---------------------
2 files changed, 10 insertions(+), 21 deletions(-)
--- a/Documentation/dev-tools/kasan.rst~mm-page_owner-decouple-freeing-stack-trace-from-debug_pagealloc
+++ a/Documentation/dev-tools/kasan.rst
@@ -41,6 +41,9 @@ smaller binary while the latter is 1.1 -
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:
--- a/mm/page_owner.c~mm-page_owner-decouple-freeing-stack-trace-from-debug_pagealloc
+++ a/mm/page_owner.c
@@ -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
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_own
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_stac
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 *pag
{
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
+ handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
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_owner = get_page_owner(page_ext);
+ page_owner->free_handle = handle;
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",
_
