linux-kernel - Re: [RFC PATCH v9 06/27] mm: Introduce VM

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Message-ID: <021394ef-e552-0639-0294-472e32e0d3fc@intel.com>
Date:   Wed, 26 Feb 2020 10:07:54 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>, 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>,
        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>, x86-patch-review@...el.com
Subject: Re: [RFC PATCH v9 06/27] mm: Introduce VM_SHSTK for Shadow Stack
 memory

On 2/5/20 10:19 AM, Yu-cheng Yu wrote:
> A Shadow Stack (SHSTK) PTE must be read-only and have _PAGE_DIRTY set.
> However, read-only and Dirty PTEs also exist for copy-on-write (COW) pages.
> These two cases are handled differently for page faults and a new VM flag
> is necessary for tracking SHSTK VMAs.
> 
> v9:
> - Add VM_SHSTK case to arch_vma_name().
> - Revise the commit log to explain why a new VM flag is needed.

To be honest, a flag is not strictly *needed*.  It is certainly
convenient and straightforward, but it's far from being truly necessary.