From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Fri, 2 Mar 2018 10:30:46 +0000 Subject: [PATCH 00/45] arm Spectre fix backport review for LTS 4.9 In-Reply-To: References: <1519908862-11425-1-git-send-email-alex.shi@linaro.org> <20180301164630.GB23321@kroah.com> Message-ID: <20180302103046.GC19323@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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