Re: [PATCH v26 23/30] x86/cet/shstk: Handle thread shadow stack

Yu, Yu-cheng
2021-05-11T18:35:13Z

On 5/10/2021 7:15 AM, Borislav Petkov wrote:
> On Tue, Apr 27, 2021 at 01:43:08PM -0700, Yu-cheng Yu wrote:
>> @@ -181,6 +184,12 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg,
>> if (clone_flags & CLONE_SETTLS)
>> ret = set_new_tls(p, tls);
>>
>> +#ifdef CONFIG_X86_64
>
> IS_ENABLED
>
>> + /* Allocate a new shadow stack for pthread */
>> + if (!ret)
>> + ret = shstk_setup_thread(p, clone_flags, stack_size);
>> +#endif
>> +
>
> And why is this addition here...
>
>> if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP)))
>> io_bitmap_share(p);
>
> ... instead of here?
>
> <---
>

io_bitmap_share() does refcount_inc(&current->thread.io_bitmap->refcnt),
and the function won't fail. However, shadow stack allocation can fail.
So, maybe leave io_bitmap_share() at the end?

Thanks,
Yu-cheng