From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Woodhouse, David" Subject: Re: [RFC 04/10] x86/mm: Only flush indirect branches when switching into non dumpable process Date: Sat, 20 Jan 2018 21:06:04 +0000 Message-ID: <1516482364.9814.18.camel@amazon.co.uk> References: <1516476182-5153-1-git-send-email-karahmed@amazon.de> <1516476182-5153-5-git-send-email-karahmed@amazon.de> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=sha-256; protocol="application/x-pkcs7-signature"; boundary="=-sZWo+Mycbp5Snswlgb+j" Cc: Andi Kleen , Andrea Arcangeli , Andy Lutomirski , 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 Hiramatsu , Paolo Bonzini , Peter Zijlstra < To: KarimAllah Ahmed , Return-path: Received: from smtp-fw-6002.amazon.com ([52.95.49.90]:57298 "EHLO smtp-fw-6002.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756684AbeATVJZ (ORCPT ); Sat, 20 Jan 2018 16:09:25 -0500 Received: from uc8d3ff76b9bc5848a9cc.ant.amazon.com (pdx2-ws-svc-lb17-vlan2.amazon.com [10.247.140.66]) by email-inbound-relay-2b-2eab95aa.us-west-2.amazon.com (8.14.7/8.14.7) with ESMTP id w0KL9ExO049729 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Sat, 20 Jan 2018 21:09:15 GMT Received: from uc8d3ff76b9bc5848a9cc.ant.amazon.com (localhost [127.0.0.1]) by uc8d3ff76b9bc5848a9cc.ant.amazon.com (8.15.2/8.15.2/Debian-3) with ESMTP id w0KL9DIg028105 for ; Sat, 20 Jan 2018 21:09:13 GMT Received: (from dwmw@localhost) by uc8d3ff76b9bc5848a9cc.ant.amazon.com (8.15.2/8.15.2/Submit) id w0KL9Cn6028104 for kvm@vger.kernel.org; Sat, 20 Jan 2018 21:09:12 GMT In-Reply-To: <1516476182-5153-5-git-send-email-karahmed@amazon.de> Sender: kvm-owner@vger.kernel.org List-ID: --=-sZWo+Mycbp5Snswlgb+j Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sat, 2018-01-20 at 20:22 +0100, KarimAllah Ahmed wrote: > From: Tim Chen I think this is probably From: Andi now rather than From: Tim? We do need the series this far in order to have a full retpoline-based mitigation, and I'd like to see that go in sooner rather than later. There's a little more discussion to be had about the IBRS parts which come later in the series (and the final one or two which weren't posted yet). I think this is the one patch of the "we want this now" IBPB set that we expect serious debate on, which is why it's still a separate "optimisation" patch on top of the previous one which just does IBPB unconditionally. > Flush indirect branches when switching into a process that marked > itself non dumpable.=C2=A0=C2=A0This protects high value processes like g= pg > better, without having too high performance overhead. >=20 > Signed-off-by: Andi Kleen > Signed-off-by: David Woodhouse > Signed-off-by: KarimAllah Ahmed > --- > =C2=A0arch/x86/mm/tlb.c | 13 ++++++++++++- > =C2=A01 file changed, 12 insertions(+), 1 deletion(-) >=20 > diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c > index 304de7d..f64e80c 100644 > --- a/arch/x86/mm/tlb.c > +++ b/arch/x86/mm/tlb.c > @@ -225,8 +225,19 @@ void switch_mm_irqs_off(struct mm_struct *prev, stru= ct mm_struct *next, > =C2=A0 =C2=A0* Avoid user/user BTB poisoning by flushing the branch pred= ictor > =C2=A0 =C2=A0* when switching between processes. This stops one process = from > =C2=A0 =C2=A0* doing Spectre-v2 attacks on another. > + =C2=A0* > + =C2=A0* As an optimization: Flush indirect branches only when > + =C2=A0* switching into processes that disable dumping. > + =C2=A0* > + =C2=A0* This will not flush when switching into kernel threads. > + =C2=A0* But it would flush when switching into idle and back > + =C2=A0* > + =C2=A0* It might be useful to have a one-off cache here > + =C2=A0* to also not flush the idle case, but we would need some > + =C2=A0* kind of stable sequence number to remember the previous mm. > =C2=A0 =C2=A0*/ > - indirect_branch_prediction_barrier(); > + if (tsk && tsk->mm && get_dumpable(tsk->mm) !=3D SUID_DUMP_USER) > + indirect_branch_prediction_barrier(); > =C2=A0 > =C2=A0 if (IS_ENABLED(CONFIG_VMAP_STACK)) { > =C2=A0 /* --=-sZWo+Mycbp5Snswlgb+j Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 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