Re: [PATCH 00/45] arm Spectre fix backport review for LTS 4.9

[Alex Shi]

On 03/02/2018 06:30 PM, Will Deacon wrote:
> 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.
> 


Thanks for comments, Will!

Yes, I full understand the difference between SoCs. Thanks for point it out!


Regards
Alex