Re: [PATCH] kasan: account for new sections when instrumenting globals

[Dmitry Vyukov <dvyukov@google.com>]

On Thu, Jun 23, 2016 at 3:06 PM, Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
> 2016-06-23 15:40 GMT+03:00 Dmitry Vyukov <dvyukov@google.com>:
>> On Thu, Jun 23, 2016 at 1:50 PM, Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
>>> 2016-06-23 14:49 GMT+03:00 Andrey Ryabinin <ryabinin.a.a@gmail.com>:
>>>
>>>> Frankly, I don't understand why .text.[exit,startup] sections has any relation
>>>> to the bug you described, but maybe I just don't now linker
>>>
>>> ... scripting well enough to understand what's going on here.
>>
>>
>> I noticed that these 3 new sections are what's different between
>> kernel that works and kernel that does not work. So I decided to
>> account all of them
>> Checked now, it works only with .dtors.
>> Is it preferable to add only .dtors or all sections?
>
> No. Merging text.startup/text.exit into INIT_TEXT/EXIT_TEXT makes sense anyway.
> This will save us some memory. Also we can add .fini_array into
> DISCARD section, because we don't need destructors.
>
> As for .dtors, at first I'd like to understand where it comes from.
> AFAIU it shouldn't exist at all.
> Recent gcc should generate .fini_array instead of .dtors -
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46770
> So something is wrong here. Can you share your kernel .config, kernel version?
> And you use gcc-6.1.0, right?

gcc version 6.1.1 20160513

.dtors contains asan destructors for global vars:

  [18] .dtors            PROGBITS         ffffffff8279a600  016c7600
       0000000000002e20  0000000000000000  WA       0     0     8

016c7600  00 1b b4 81 ff ff ff ff  20 1b b4 81 ff ff ff ff  |........ .......|
016c7610  40 1b b4 81 ff ff ff ff  60 1b b4 81 ff ff ff ff  |@.......`.......|
016c7620  80 1b b4 81 ff ff ff ff  a0 1b b4 81 ff ff ff ff  |................|
016c7630  c0 1b b4 81 ff ff ff ff  e0 1b b4 81 ff ff ff ff  |................|

vmlinux.old:ffffffff81b41b20 0000000000000017 t
_GLOBAL__sub_D_65535_0_init_uts_ns
vmlinux.old:ffffffff81b41b40 0000000000000017 t
_GLOBAL__sub_D_65535_0_root_mountflags
vmlinux.old:ffffffff81b41b60 0000000000000017 t _GLOBAL__sub_D_65535_0_rd_prompt
vmlinux.old:ffffffff81b41b80 0000000000000017 t
_GLOBAL__sub_D_65535_0_initrd_load

ffffffff81b41b20 <_GLOBAL__sub_D_65535_0_init_uts_ns>:
ffffffff81b41b20:       55                      push   %rbp
ffffffff81b41b21:       be 03 00 00 00          mov    $0x3,%esi
ffffffff81b41b26:       48 c7 c7 a0 23 21 82    mov    $0xffffffff822123a0,%rdi
ffffffff81b41b2d:       48 89 e5                mov    %rsp,%rbp
ffffffff81b41b30:       e8 9b 85 83 ff          callq
ffffffff8137a0d0 <__asan_unregister_globals>
ffffffff81b41b35:       5d                      pop    %rbp
ffffffff81b41b36:       c3                      retq
ffffffff81b41b37:       66 0f 1f 84 00 00 00    nopw   0x0(%rax,%rax,1)
ffffffff81b41b3e:       00 00