On 9/12/19 5:31 PM, Vlastimil Babka wrote: > On 9/12/19 4:08 PM, Walter Wu wrote: >> >>> 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. > >> 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.
