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Message-ID: <1516573213.9814.117.camel@amazon.co.uk>
Subject: Re: [RFC 04/10] x86/mm: Only flush indirect branches when
 switching into non dumpable process
To:     Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
CC:     KarimAllah Ahmed <karahmed@amazon.de>,
        <linux-kernel@vger.kernel.org>, Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Andy Lutomirski" <luto@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        "Ashok Raj" <ashok.raj@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        "Borislav Petkov" <bp@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>,
        Joerg Roedel <joro@8bytes.org>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Laura Abbott <labbott@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>, <kvm@vger.kernel.org>,
        <x86@kernel.org>, "Dave Hansen" <dave@sr71.net>
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Content-Type: multipart/signed; micalg=sha-256; protocol="application/x-pkcs7-signature"; boundary="=-PQiAzReV+niBcWeFX6zM"
Date:   Sun, 21 Jan 2018 22:20:13 +0000
MIME-Version: 1.0
From:   "Woodhouse, David" <dwmw@amazon.co.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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Content-Type: text/plain; charset="UTF-8"
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On Sun, 2018-01-21 at 17:21 +0100, Ingo Molnar wrote:
>=20
> Because putting something like this into an ELF flag raises the question =
of who is=C2=A0
> allowed to set the flag - does a user-compiled binary count? If yes then =
it would=C2=A0
> be a trivial thing for local exploits to set the flag and turn off the ba=
rrier.

You can only allow *yourself* to be exploited that way. The flag says,
"I'm OK, you don't need to protect me".

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