linux-kernel - Re: [PATCH 02/35] x86/cet/shstk: Add Kconfig option for Shadow Stack

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Message-ID: <87sfstvjh9.ffs@tglx>
Date:   Tue, 08 Feb 2022 09:41:06 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dave Hansen <dave.hansen@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, 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>,
        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>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH 02/35] x86/cet/shstk: Add Kconfig option for Shadow Stack

On Mon, Feb 07 2022 at 14:39, Dave Hansen wrote:

> On 1/30/22 13:18, Rick Edgecombe wrote:
>> +config X86_SHADOW_STACK
>> +	prompt "Intel Shadow Stack"
>> +	def_bool n
>> +	depends on AS_WRUSS
>> +	depends on ARCH_HAS_SHADOW_STACK
>> +	select ARCH_USES_HIGH_VMA_FLAGS
>> +	help
>> +	  Shadow Stack protection is a hardware feature that detects function
>> +	  return address corruption.  This helps mitigate ROP attacks.
>> +	  Applications must be enabled to use it, and old userspace does not
>> +	  get protection "for free".
>> +	  Support for this feature is present on Tiger Lake family of
>> +	  processors released in 2020 or later.  Enabling this feature
>> +	  increases kernel text size by 3.7 KB.
>
> I guess the "2020" comment is still OK.  But, given that it's on AMD and
> a could of other Intel models, maybe we should just leave this at:
>
> 	CPUs supporting shadow stacks were first released in 2020.

Yes.

> If we say anything.  We mostly want folks to just go read the
> documentation if they needs more details.

Also the kernel text size increase blurb is pretty useless as that's a
number which is wrong from day one.

Thanks,

        tglx