On 9/12/19 5:31 PM, Vlastimil Babka wrote:

On 9/12/19 4:08 PM, Walter Wu wrote:

quoted

quoted

  extern void __reset_page_owner(struct page *page, unsigned int order);

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index 6c9682ce0254..dc560c7562e8 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan

@@ -41,6 +41,8 @@ config KASAN_GENERIC

      select SLUB_DEBUG if SLUB
      select CONSTRUCTORS
      select STACKDEPOT
+    select PAGE_OWNER
+    select PAGE_OWNER_FREE_STACK
      help
        Enables generic KASAN mode.
        Supported in both GCC and Clang. With GCC it requires version 4.9.2

@@ -63,6 +65,8 @@ config KASAN_SW_TAGS

      select SLUB_DEBUG if SLUB
      select CONSTRUCTORS
      select STACKDEPOT
+    select PAGE_OWNER
+    select PAGE_OWNER_FREE_STACK
      help

What is the difference between PAGE_OWNER+PAGE_OWNER_FREE_STACK and
DEBUG_PAGEALLOC?

Same memory usage, but debug_pagealloc means also extra checks and restricting memory access to freed pages to catch UAF.

quoted

If you directly enable PAGE_OWNER+PAGE_OWNER_FREE_STACK
PAGE_OWNER_FREE_STACK,don't you think low-memory device to want to use
KASAN?

OK, so it should be optional? But I think it's enough to distinguish no PAGE_OWNER at all, and PAGE_OWNER+PAGE_OWNER_FREE_STACK together - I don't see much point in PAGE_OWNER only for this kind of debugging.

So how about this? KASAN wouldn't select PAGE_OWNER* but it would be recommended in the help+docs. When PAGE_OWNER and KASAN are selected by user, PAGE_OWNER_FREE_STACK gets also selected, and both will be also runtime enabled without explicit page_owner=on.
I mostly want to avoid another boot-time option for enabling PAGE_OWNER_FREE_STACK.
Would that be enough flexibility for low-memory devices vs full-fledged debugging?

Originally I thought that with you patch users still can disable page_owner via "page_owner=off" boot param.
But now I realized that this won't work. I think it should work, we should allow users to disable it.



Or another alternative option (and actually easier one to implement), leave PAGE_OWNER as is (no "select"s in Kconfigs)
Make PAGE_OWNER_FREE_STACK like this:

+config PAGE_OWNER_FREE_STACK
+	def_bool KASAN || DEBUG_PAGEALLOC
+	depends on PAGE_OWNER
+

So, users that want alloc/free stack will have to enable CONFIG_PAGE_OWNER=y and add page_owner=on to boot cmdline.


Basically the difference between these alternative is whether we enable page_owner by default or not. But there is always a possibility to disable it.


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