linux-kernel - Re: [RFC 04/10] x86/mm: Only flush indirect branches when switching into non dumpable process

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Message-ID: <1516573213.9814.117.camel@amazon.co.uk>
Date:   Sun, 21 Jan 2018 22:20:13 +0000
From:   "Woodhouse, David" <dwmw@...zon.co.uk>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
CC:     KarimAllah Ahmed <karahmed@...zon.de>,
        <linux-kernel@...r.kernel.org>, Andi Kleen <ak@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Andy Lutomirski" <luto@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        "Ashok Raj" <ashok.raj@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        "Borislav Petkov" <bp@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Laura Abbott <labbott@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>, <kvm@...r.kernel.org>,
        <x86@...nel.org>, "Dave Hansen" <dave@...1.net>
Subject: Re: [RFC 04/10] x86/mm: Only flush indirect branches when
 switching into non dumpable process

On Sun, 2018-01-21 at 17:21 +0100, Ingo Molnar wrote:
> 
> Because putting something like this into an ELF flag raises the question of who is 
> allowed to set the flag - does a user-compiled binary count? If yes then it would 
> be a trivial thing for local exploits to set the flag and turn off the barrier.

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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