From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-1243504-1519986646-2-15615725079463812923 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, RCVD_IN_DNSWL_HI -5, SPF_PASS -0.001, T_RP_MATCHES_RCVD -0.01, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='217.140.101.70', Host='foss.arm.com', Country='US', FromHeader='com', MailFrom='com' X-Spam-charsets: plain='us-ascii' X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: will.deacon@arm.com ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=arctest; t=1519986646; b=A8LXAUp+ggRz0FmavvDL4CB4xBtPJz3naVvxqgkNnWsJVoJ bU4DoYCQ6z+ToRweAav/7XYBh4axZ5Boje9R5lbUMlHmJFzU/QkL/4TXpy1ei1zE 2s75LIp0agUCTxP3kqhLCFgWQdYCfqi/cEmSA5UCO6MEZzGYOtLBoP70CSaoNL8n URLtvLPHDs7DxL32XRp048WKM75DwvMzOb6AOmCCPfX/FpMbJp+ANDRw2wJvX37I jX1tDP01essOcwMnWo0VyZD2UmtpmPWIrCuEDhvcTcUJOojpll7ywesw4tVNVXSr AZ5NcMmuZuz5uS7UO2rgNo9BZbXP+wEAQGNAO1g== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=date:from:to:cc:subject:message-id :references:mime-version:content-type:in-reply-to; s=arctest; t= 1519986646; bh=vOOVzcwPhmBSwCLGwYpbX4mCIGrwz7TAKHf72KqJ0Bc=; b=L 9Z34nHlLnJ6lQzktPHtA5HBw7umI+pHS3kSj2ZCU2ebM4tac2GJHyIR8cFBqYZP5 176PO3DTSrBkSIJiwPu4ROnd9JR7n7aDOtg/bqNCGsSW0HhqoHV1dmQvNAhN3EsR COhL5XfrsF8W1GbOlqKnPn9JottsEXWLzyeWNcKZk5WRippQ0PKjFWI0/IymKB52 LYvqwzMmbQyOtKQb1UTe/mqCebduWo5sPuDtWuKU7wXkqLRRIAO54wjA2YxbxHWc RIfKmaNJLjAJByfHFW+ykn/6+ztccFVCvojQJB8jFxIKyZbQsNPpeq9GUO1s2+bO fTNe18VBBElr4Xqsccsyw== ARC-Authentication-Results: i=1; mx5.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,d=none) header.from=arm.com; iprev=pass policy.iprev=217.140.101.70 (foss.arm.com,usa-sjc-mx-foss1.foss.arm.com); spf=pass smtp.mailfrom=will.deacon@arm.com smtp.helo=foss.arm.com; x-aligned-from=pass; x-ptr=pass x-ptr-helo=foss.arm.com x-ptr-lookup=foss.arm.com,usa-sjc-mx-foss1.foss.arm.com; x-return-mx=pass smtp.domain=arm.com smtp.result=pass smtp_is_org_domain=yes header.domain=arm.com header.result=pass header_is_org_domain=yes Authentication-Results: mx5.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,d=none) header.from=arm.com; iprev=pass policy.iprev=217.140.101.70 (foss.arm.com,usa-sjc-mx-foss1.foss.arm.com); spf=pass smtp.mailfrom=will.deacon@arm.com smtp.helo=foss.arm.com; x-aligned-from=pass; x-ptr=pass x-ptr-helo=foss.arm.com x-ptr-lookup=foss.arm.com,usa-sjc-mx-foss1.foss.arm.com; x-return-mx=pass smtp.domain=arm.com smtp.result=pass smtp_is_org_domain=yes header.domain=arm.com header.result=pass header_is_org_domain=yes Date: Fri, 2 Mar 2018 10:30:46 +0000 From: Will Deacon To: Alex Shi Cc: Greg KH , Marc Zyngier , Ard Biesheuvel , Catalin Marinas , stable@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 00/45] arm Spectre fix backport review for LTS 4.9 Message-ID: <20180302103046.GC19323@arm.com> References: <1519908862-11425-1-git-send-email-alex.shi@linaro.org> <20180301164630.GB23321@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Fri, Mar 02, 2018 at 05:02:32PM +0800, Alex Shi wrote: > As testing the spectre bug fix, that's a good question. I also asked > this question to original patch authors, like Marc. They said they just > figure out these patches could block spectre or meltdown issue. From my > side, I just reproduced the process internal spectre. But all fix on arm > can not resolve the user space internal spectre. It can block from user > to kernel or kernel to user spectre according the code purose. So I > believe these patch could do their job. And arm cpu would drop the > spectre branches if it has 20+ 'nop' instructions... Since this is archived on a public list and I don't want people to rely on this, no, you cannot rely on "20+ 'nop' instructions" to work around spectre on arm/arm64. It might prevent a particular PoC working on a particular SoC, but it's fragile at best. Will