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References: <1516476182-5153-1-git-send-email-karahmed@amazon.de>
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From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Sun, 21 Jan 2018 06:07:11 -0800
Message-ID: <CAMe9rOqJHATOc0GJMM-+Zf9_+7EFYXDPazreJ_KiPNnOGDEd+g@mail.gmail.com>
Subject: Re: [RFC 04/10] x86/mm: Only flush indirect branches when switching
 into non dumpable process
To: David Woodhouse <dwmw2@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>, KarimAllah Ahmed <karahmed@amazon.de>,
	LKML <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>, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <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
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On Sun, Jan 21, 2018 at 4:04 AM, David Woodhouse <dwmw2@infradead.org> wrote:
>
>> 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?
>
>
> Spectre V2 not v1. V1 is separate.
> For V2 retpoline is enough... as long as all the libraries have it too.
>
>> So would it make sense to provide an ELF flag / personality thing such
>> that userspace can indicate its spectre-safe?
>
> Yes, Arjan and I were pondering that yesterday; it probably does make
> sense. Also for allowing a return to userspace after vmexit, if the army
> process itself is so marked.

Please take a look at how CET is handled in program property in
x86-64 psABI for CET:

https://github.com/hjl-tools/x86-psABI/wiki/x86-64-psABI-cet.pdf


-- 
H.J.