linux-kernel - Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function

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Message-Id: <4F7D0C3C-F239-4B67-BB05-31350F809293@amacapital.net>
Date:   Fri, 7 Jun 2019 15:27:16 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>, 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>,
        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: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function


> On Jun 7, 2019, at 2:09 PM, Dave Hansen <dave.hansen@...el.com> wrote:
> 
> On 6/7/19 1:06 PM, Yu-cheng Yu wrote:
>>> Huh, how does glibc know about all possible past and future legacy code
>>> in the application?
>> When dlopen() gets a legacy binary and the policy allows that, it will manage
>> the bitmap:
>> 
>>  If a bitmap has not been created, create one.
>>  Set bits for the legacy code being loaded.
> 
> I was thinking about code that doesn't go through GLIBC like JITs.

CRIU is another consideration: it would be rather annoying if CET programs can’t migrate between LA57 and normal machines.