linux-kernel - Re: [PATCH 25/35] x86/cet/shstk: Add user-mode shadow stack support

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Message-ID: <bbcf2cf9-e039-0fba-457c-40455b8acf65@intel.com>
Date:   Fri, 11 Feb 2022 16:11:03 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Andy Lutomirski <luto@...nel.org>,
        Rick P Edgecombe <rick.p.edgecombe@...el.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, Linux API <linux-api@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        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 (Intel)" <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Moreira, Joao" <joao.moreira@...el.com>,
        "john.allen@....com" <john.allen@....com>,
        "kcc@...gle.com" <kcc@...gle.com>,
        "Eranian, Stephane" <eranian@...gle.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH 25/35] x86/cet/shstk: Add user-mode shadow stack support

On 2/11/22 16:07, Andy Lutomirski wrote:
> On Fri, Feb 11, 2022, at 3:37 PM, Dave Hansen wrote:
>> On 1/30/22 13:18, Rick Edgecombe wrote:
>>> Add the user shadow stack MSRs to the xsave helpers, so they can be used
>>> to implement the functionality.
>> Do these MSRs ever affect kernel-mode operation?
>>
>> If so, we might need to switch them more aggressively at context-switch
>> time like PKRU.
>>
>> If not, they can continue to be context-switched with the PASID state
>> which does not affect kernel-mode operation.
> PASID?  PASID is all kinds of weird.  I assume you mean switching it
> with all the normal state.

I was grouping PASID along with the CET MSRs because they're the only
supervisor state.  But, yeah, it's all XRSTOR'd at the same spot right
now, user or kernel.