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

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Message-Id: <4eeab037-502c-4d8d-84da-e29203dad6ad@www.fastmail.com>
Date:   Fri, 11 Feb 2022 16:07:51 -0800
From:   "Andy Lutomirski" <luto@...nel.org>
To:     "Dave Hansen" <dave.hansen@...el.com>,
        "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 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.

>
> Either way, it would be nice to have some changelog material to that effect.