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

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Message-ID: <a645aefc-632f-b1eb-4f4e-1c5b0f9e75d5@intel.com>
Date:   Tue, 11 May 2021 11:35:03 -0700
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Haitao Huang <haitao.huang@...el.com>
Subject: Re: [PATCH v26 23/30] x86/cet/shstk: Handle thread shadow stack

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