linux-kernel - Re: [PATCH v19 02/25] x86/cet/shstk: Add Kconfig option for user-mode control-flow protection

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Message-ID: <19793d76-6793-20a0-059c-cd153cf36a8b@intel.com>
Date:   Thu, 4 Feb 2021 16:05:04 -0800
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Kees Cook <keescook@...omium.org>
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>,
        Borislav Petkov <bp@...en8.de>,
        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>,
        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>
Subject: Re: [PATCH v19 02/25] x86/cet/shstk: Add Kconfig option for user-mode
 control-flow protection

On 2/4/2021 11:56 AM, Kees Cook wrote:
> On Wed, Feb 03, 2021 at 02:55:24PM -0800, Yu-cheng Yu wrote:
>> Shadow Stack provides protection against function return address
>> corruption.  It is active when the processor supports it, the kernel has
>> CONFIG_X86_CET enabled, and the application is built for the feature.
>> This is only implemented for the 64-bit kernel.  When it is enabled, legacy
>> non-Shadow Stack applications continue to work, but without protection.
>>
>> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
>> ---
>>   arch/x86/Kconfig           | 22 ++++++++++++++++++++++
>>   arch/x86/Kconfig.assembler |  5 +++++
>>   2 files changed, 27 insertions(+)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 21f851179ff0..074b3c0e6bf6 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -1951,6 +1951,28 @@ config X86_SGX
>>   
>>   	  If unsure, say N.
>>   
>> +config ARCH_HAS_SHADOW_STACK
>> +	def_bool n
>> +
>> +config X86_CET
>> +	prompt "Intel Control-flow protection for user-mode"
>> +	def_bool n
>> +	depends on X86_64
>> +	depends on AS_WRUSS
>> +	select ARCH_USES_HIGH_VMA_FLAGS
>> +	select ARCH_HAS_SHADOW_STACK
> 
> This seems backwards to me? Shouldn't 'config X86_64' do the 'select
> ARCH_HAS_SHADOW_STACK' and 'config X86_CET' do a 'depends on
> ARCH_HAS_SHADOW_STACK' instead?

I will change it.  Thanks!

--
Yu-cheng