linux-kernel - Re: [RFC PATCH 1/3] mm: Introduce VM

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Message-Id: <CBB8C19E-7F65-4D43-9783-6383478700A1@amacapital.net>
Date:   Fri, 28 Jun 2019 14:49:32 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
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>,
        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>
Subject: Re: [RFC PATCH 1/3] mm: Introduce VM_IBT for CET legacy code bitmap



> On Jun 28, 2019, at 12:41 PM, Yu-cheng Yu <yu-cheng.yu@...el.com> wrote:
> 
> The previous discussion of the IBT legacy code bitmap is here:
> 
>    https://lkml.org/lkml/2019/6/6/1032
> 
> When CET Indirect Branch Tracking (IBT) is enabled, the processor expects
> every branch target is an ENDBR instruction, or the target's address is
> marked as legacy in the legacy code bitmap.  The bitmap covers the whole
> user-mode address space (TASK_SIZE_MAX for 64-bit, TASK_SIZE for IA32),
> and each bit represents one page of linear address range.
> 
> This patch introduces VM_IBT for the bitmap.

There’s no need to allocate a bit for this and to clutter up the fault code with special cases. Use _install_special_mapping(), please.  If you need to make it more flexible to cover your use case, please do so.