From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation Date: Wed, 24 Jan 2018 01:22:03 +0000 Message-ID: <1516756923.13558.62.camel@infradead.org> References: <1516476182-5153-1-git-send-email-karahmed@amazon.de> <1516476182-5153-10-git-send-email-karahmed@amazon.de> <243BE571-AF73-44B3-8D17-193F9E07686A@amacapital.net> <4e01a7a9-29e4-adcc-3f53-550fb7f3d370@amd.com> <1516724457.9521.156.camel@amazon.co.uk> <20180123224956.GQ7844@tassilo.jf.intel.com> <1516749276.13558.25.camel@amazon.co.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-Jacf2AEHFbfvBuQEC/Bc" Cc: Andi Kleen , Tom Lendacky , KarimAllah Ahmed , LKML , Andrea Arcangeli , Arjan van de Ven , Ashok Raj , Asit Mallick , Borislav Petkov , Dan Williams , Dave Hansen , Greg Kroah-Hartman , "H . Peter Anvin" , Ingo Molnar , Janakarajan Natarajan , Joerg Roedel , Jun Nakajima , Laura Abbott , Linus Torvalds , Masami Hiramat To: Andy Lutomirski , Tim Chen Return-path: Received: from twosheds.infradead.org ([90.155.92.209]:41752 "EHLO twosheds.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751945AbeAXBWL (ORCPT ); Tue, 23 Jan 2018 20:22:11 -0500 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: --=-Jacf2AEHFbfvBuQEC/Bc Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2018-01-23 at 17:00 -0800, Andy Lutomirski wrote: > On Tue, Jan 23, 2018 at 4:47 PM, Tim Chen wr= ote: > >=20 > > On 01/23/2018 03:14 PM, Woodhouse, David wrote: > > >=20 > > > On Tue, 2018-01-23 at 14:49 -0800, Andi Kleen wrote: > > > >=20 > > > > >=20 > > > > > Not sure.=C2=A0=C2=A0Maybe to start, the answer might be to allow= it to be set for > > > > > the ultra-paranoid, but in general don't enable it by default.=C2= =A0=C2=A0Having it > > > > > enabled would be an alternative to someone deciding to disable SM= T, since > > > > > that would have even more of a performance impact. > > > > I agree. A reasonable strategy would be to only enable it for > > > > processes that have dumpable disabled. This should be already set f= or > > > > high value processes like GPG, and allows others to opt-in if > > > > they need to. > > > That seems to make sense, and I think was the solution we were > > > approaching for IBPB on context switch too, right? > > >=20 > > > Are we generally agreed on dumpable as the criterion for both of thos= e? > > >=20 > > It is a reasonable approach.=C2=A0=C2=A0Let a process who needs max sec= urity > > opt in with disabled dumpable. It can have a flush with IBPB clear befo= re > > starting to run, and have STIBP set while running. > >=20 > Do we maybe want a separate opt in?=C2=A0=C2=A0I can easily imagine thing= s like > web browsers that *don't* want to be non-dumpable but do want this > opt-in. =C2=A0 This is to protect you from another local process running on a HT sibling. Not the kind of thing that web browsers are normally worrying about. > Also, what's the performance hit of STIBP? Varies per CPU generation, but generally approaching that of full IBRS I think? 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