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From:   "H.J. Lu" <hjl.tools@gmail.com>
Date:   Mon, 9 Mar 2020 14:12:31 -0700
Message-ID: <CAMe9rOqf0OHL9397Vikgb=UWhRMf+FmGq-9VAJNmfmzNMMDkCw@mail.gmail.com>
Subject: Re: [RFC PATCH v9 01/27] Documentation/x86: Add CET description
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Andy Lutomirski <luto@amacapital.net>,
        Yu-cheng Yu <yu-cheng.yu@intel.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, linux-doc@vger.kernel.org,
        Linux-MM <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
        Dave Martin <Dave.Martin@arm.com>, x86-patch-review@intel.com
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On Mon, Mar 9, 2020 at 1:59 PM Dave Hansen <dave.hansen@intel.com> wrote:
>
> On 3/9/20 1:54 PM, H.J. Lu wrote:
> >> If a program with the magic ELF CET flags missing can=E2=80=99t make a
> >> thread with IBT and/or SHSTK enabled, then I think we=E2=80=99ve made =
an
> >> error and should fix it.
> >>
> > A non-CET program can start a CET program and vice versa.
>
> Could we be specific here, please?
>
> HJ are you saying that:
> * CET program can execve() a non-CET program, and
> * a non-CET program can execve() a CET program
>
> ?

Yes.

> That's obvious.
>
> But what are the rules for clone()?  Should there be rules for
> mismatches for CET enabling between threads if a process (not child
> processes)?

What did you mean? A threaded application is either CET enabled or not
CET enabled.   A new thread from clone makes no difference.

--=20
H.J.