Re: [PATCH v6 00/39] kasan, vmalloc, arm64: add vmalloc tagging support for SW/HW_TAGS

[Andrey Konovalov]

On Thu, Apr 28, 2022 at 4:14 PM Qian Cai <quic_qiancai@xxxxxxxxxxx> wrote:
>
> > SW_TAGS vmalloc tagging support is straightforward. It reuses all of
> > the generic KASAN machinery, but uses shadow memory to store tags
> > instead of magic values. Naturally, vmalloc tagging requires adding
> > a few kasan_reset_tag() annotations to the vmalloc code.
>
> I could use some help here. Ever since this series, our system starts to
> trigger bad page state bugs from time to time. Any thoughts?
>
>  BUG: Bad page state in process systemd-udevd  pfn:83ffffcd
>  page:fffffc20fdfff340 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x83ffffcd
>  flags: 0xbfffc0000001000(reserved|node=0|zone=2|lastcpupid=0xffff)
>  raw: 0bfffc0000001000 fffffc20fdfff348 fffffc20fdfff348 0000000000000000
>  raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
>  page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
>  page_owner info is not present (never set?)

Hi Qian,

No ideas so far.

Looks like the page has reserved tag set when it's being freed.

Does this crash only happen with the SW_TAGS mode?

Does this crash only happen when loading modules?

Does your system have any hot-plugged memory?

Thanks!