On Fri, Feb 8, 2019 at 5:16 AM Qian Cai <cai@lca.pw> wrote:
>
> Kmemleak is totally busted with CONFIG_KASAN_SW_TAGS=y because most of tracking
> object pointers passed to create_object() have the upper bits set by KASAN.

Hi Qian,

Yeah, the issue is that kmemleak performs a bunch of pointer
comparisons that break when pointers are tagged. Try the attached
patch, it should fix the issue. I don't like the way this patch does
it though, I'll see if I can come up with something better.

Thanks for the report!

> However, even after applied this patch [1] to fix a few things, it still has
> many errors during boot.
>
> https://git.sr.ht/~cai/linux-debug/tree/master/dmesg
>
> What I don't understand is that even the patch did call kasan_reset_tag() in
> paint_ptr(), it still complained on objects with upper bits set which indicates
> that this line did not run.
>
> return (__s64)(value << shift) >> shift;
>
> [   42.462799] kmemleak: Trying to color unknown object at 0xffff80082df80000 as
> Grey
> [   42.470524] CPU: 128 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc5+ #17
> [   42.477153] Call trace:
> [   42.479639]  dump_backtrace+0x0/0x450
> [   42.483362]  show_stack+0x20/0x2c
> [   42.486733]  __dump_stack+0x20/0x28
> [   42.490276]  dump_stack+0xa0/0xfc
> [   42.493649]  paint_ptr+0xa8/0xf4
> [   42.496934]  kmemleak_not_leak+0xa4/0x15c
> [   42.501013]  init_section_page_ext+0x1bc/0x328
> [   42.505528]  page_ext_init+0x4dc/0x75c
> [   42.509336]  kernel_init_freeable+0x684/0x1104
> [   42.513857]  kernel_init+0x18/0x2a4
> [   42.517407]  ret_from_fork+0x10/0x18
>
> [1]
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index f9d9dc250428..70343d887f34 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -588,7 +588,7 @@ static struct kmemleak_object *create_object(unsigned long
> ptr, size_t size,
>         spin_lock_init(&object->lock);
>         atomic_set(&object->use_count, 1);
>         object->flags = OBJECT_ALLOCATED;
> -       object->pointer = ptr;
> +       object->pointer = (unsigned long)kasan_reset_tag((void *)ptr);
>         object->size = size;
>         object->excess_ref = 0;
>         object->min_count = min_count;
> @@ -748,11 +748,12 @@ static void paint_it(struct kmemleak_object *object, int
> color)
>  static void paint_ptr(unsigned long ptr, int color)
>  {
>         struct kmemleak_object *object;
> +       unsigned long addr = (unsigned long)kasan_reset_tag((void *)ptr);
>
> -       object = find_and_get_object(ptr, 0);
> +       object = find_and_get_object(addr, 0);
>         if (!object) {
>                 kmemleak_warn("Trying to color unknown object at 0x%08lx as %s\n",
> -                             ptr,
> +                             addr,
>                               (color == KMEMLEAK_GREY) ? "Grey" :
>                               (color == KMEMLEAK_BLACK) ? "Black" : "Unknown");
>                 return;
>
>