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Date:   Sun, 21 Jan 2018 12:22:24 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     KarimAllah Ahmed <karahmed@amazon.de>
Cc:     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>,
        David Woodhouse <dwmw@amazon.co.uk>,
        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?B?S3LEjW3DocWZ?= <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
Subject: Re: [RFC 04/10] x86/mm: Only flush indirect branches when switching
 into non dumpable process
Message-ID: <20180121112224.GH2269@hirez.programming.kicks-ass.net>
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On Sat, Jan 20, 2018 at 08:22:55PM +0100, KarimAllah Ahmed wrote:
> From: Tim Chen <tim.c.chen@linux.intel.com>
> 
> Flush indirect branches when switching into a process that marked
> itself non dumpable.  This protects high value processes like gpg
> better, without having too high performance overhead.

So if I understand it right, this is only needed if the 'other'
executable itself is susceptible to spectre. If say someone audited gpg
for spectre-v1 and build it with retpoline, it would be safe to not
issue the IBPB, right?

So would it make sense to provide an ELF flag / personality thing such
that userspace can indicate its spectre-safe?

I realize that this is all future work, because so far auditing for v1
is a lot of pain (we need better tools), but would it be something that
makes sense in the longer term?