From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: ACJfBosVsByuotC3KJEiQqkKYklzD4JxhGfc/hY7qITTpoTXRysOebWqWenUB4M2gDPMI0MVSAEp ARC-Seal: i=1; a=rsa-sha256; t=1516318541; cv=none; d=google.com; s=arc-20160816; b=XNXQSzkmR8ye+beJbUIw6yg0Tlx9tt2v2ZuY+SrkAZtTWW1J3KZQ6xKgzKYqbgEeR7 TaUFsCHXoF5tLLALTh7Rpe7GMhrP8QLmwxt162JotU119clBZeN9QqFqNzOLjnLzMC66 VKgE0WDmsyO2swVglAhvGMrJBcMbdkbKN9XuGu+KOOpIZFIbjhKNW6Bg9ydZ8byUtziZ rRZ3ZYUPck48fVT2EdPlXVQEx+X0e3lFR8GjTnenHGohyBvUW1EHaKcpOCoOdqQ07qCm UVF3z3kg7H6tkBX31BnlV2iYb0gM4jcBhiipfc47VtmCB+4JI4vuA/HwgY9LPwFGt0RO CHPw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=sender:content-language:content-transfer-encoding:in-reply-to :mime-version:user-agent:date:message-id:from:references:cc:to :subject:arc-authentication-results; bh=RmqEH6AhChccIU4X6hBGuHJjaZNqqHXPyECKdxadESI=; b=0oqeECOUt6j7xRJHV7BDTwXHoSTYCgcoKnt/Vs70rHrrn1etG9XAKFqFq0Im917Ko/ 8FQ/Zq/YWMhZKcNPWzMTvbzByE++Sin/nekXFZZW2C7/dqJ8QoaUDSLl2JKjZNx5EcAk FLzNfE+vQi6zpHpoQcN9ZrBsIGyo5dwYO/jeuyI/dVV+VoT/GeyAat8I+Qwy6kEIHn8h rL1BUP7vdyZMy/KZFnnBi1jeK3BBSlquX7rrs41Znd4R8KcZQYWxCPnQSMfpIvA6qrUZ 8W2T/Myszhm5/nfft1e01Ql1igu5G50gZjGVgQGCGayhiNH5M4jrYdnn9aXjRLB+k52Y X8Pg== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of amc96@hermes.cam.ac.uk designates 131.111.8.131 as permitted sender) smtp.mailfrom=amc96@hermes.cam.ac.uk Authentication-Results: mx.google.com; spf=pass (google.com: domain of amc96@hermes.cam.ac.uk designates 131.111.8.131 as permitted sender) smtp.mailfrom=amc96@hermes.cam.ac.uk X-Cam-AntiVirus: no malware found X-Cam-ScannerInfo: http://help.uis.cam.ac.uk/email-scanner-virus Subject: Re: [PATCH 23/35] x86/speculation: Add basic speculation control code To: Andy Lutomirski , Andrea Arcangeli Cc: Josh Poimboeuf , Paolo Bonzini , Dave Hansen , Peter Zijlstra , David Woodhouse , Thomas Gleixner , LKML , Ashok Raj , Tim Chen , Linus Torvalds , Greg KH , Andi Kleen , Arjan Van De Ven , Dan Williams , Jun Nakajima , Asit Mallick , Jason Baron References: <20180118134800.711245485@infradead.org> <20180118140152.830682032@infradead.org> <20180118163745.t5nmwdr53wjsl7o5@treble> <73a5735a-6a5b-0e0f-1f0b-e7cd955880d2@intel.com> <20180118182431.xvmk6kzxpzu43b43@treble> <20180118190842.GA14136@redhat.com> From: Andrew Cooper Message-ID: <9e771f85-ed55-6a94-ad57-b6b8f93a3413@citrix.com> Date: Thu, 18 Jan 2018 23:35:36 +0000 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-GB Sender: Andrew Cooper X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcSW1wb3J0YW50Ig==?= X-GMAIL-THRID: =?utf-8?q?1589948948566960870?= X-GMAIL-MSGID: =?utf-8?q?1589975231696738020?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 18/01/2018 23:25, Andy Lutomirski wrote: > On Thu, Jan 18, 2018 at 11:08 AM, Andrea Arcangeli wrote: >> On Thu, Jan 18, 2018 at 12:24:31PM -0600, Josh Poimboeuf wrote: >>> On Thu, Jan 18, 2018 at 06:12:36PM +0100, Paolo Bonzini wrote: >>>> On 18/01/2018 18:08, Dave Hansen wrote: >>>>> On 01/18/2018 08:37 AM, Josh Poimboeuf wrote: >>>>>>> --- a/Documentation/admin-guide/kernel-parameters.txt >>>>>>> +++ b/Documentation/admin-guide/kernel-parameters.txt >>>>>>> @@ -3932,6 +3932,7 @@ >>>>>>> retpoline - replace indirect branches >>>>>>> retpoline,generic - google's original retpoline >>>>>>> retpoline,amd - AMD-specific minimal thunk >>>>>>> + ibrs - Intel: Indirect Branch Restricted Speculation >>>>>> Are there plans to add spectre_v2=ibrs_always to prevent SMT-based >>>>>> attacks? >>>>> What does "ibrs_always" mean to you? >>> Maybe ibrs_always isn't the best name. Basically we need an option to >>> protect user-user attacks via SMT. >>> >>> It could be implemented with IBRS=1, or STIBP, or as part of the >>> mythical IBRS_ATT. >> User stibp or user ibrs would be different things, both would be valid >> for different use cases, and the user stibp should perform better. >> >> Leaving ibrs on when returning from kernel to userland (or setting >> ibrs if kernel used retpolines instead of ibrs) achieves stronger >> semantics than just setting SPEC_CTRL with stibp when returning to >> userland. > I read the whitepaper that documented the new MSRs a couple days ago > and I'm now completely unable to find it. If anyone could send the > link, that would be great. https://software.intel.com/sites/default/files/managed/c5/63/336996-Speculative-Execution-Side-Channel-Mitigations.pdf ~Andrew