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

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Message-ID: <87h88xcptn.fsf@oldenburg2.str.redhat.com>
Date:   Mon, 10 Jun 2019 19:28:36 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        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>,
        "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

* Yu-cheng Yu:

> On Fri, 2019-06-07 at 14:09 -0700, Dave Hansen 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.
>
> If JIT manages the bitmap, it knows where it is.
> It can always read the bitmap again, right?

The problem are JIT libraries without assembler code which can be marked
non-CET, such as liborc.  Our builds (e.g., orc-0.4.29-2.fc30.x86_64)
currently carries the IBT and SHSTK flag, although the entry points into
the generated code do not start with ENDBR, so that a jump to them will
fault with the CET enabled.

Thanks,
Florian