linux-kernel - Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation

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Date:   Mon, 29 Jan 2018 12:59:46 +0100
From:   Mason <slash.tmp@...e.fr>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation

[ Dropping large CC list ]

On 25/01/2018 18:16, Greg Kroah-Hartman wrote:

> On Thu, Jan 25, 2018 at 05:19:04PM +0100, Mason wrote:
> 
>> On 23/01/2018 10:30, David Woodhouse wrote:
>>
>>> Skylake takes predictions from the generic branch target buffer when
>>> the RSB underflows.
>>
>> Adding LAKML.
>>
>> AFAIU, some ARM Cortex cores have the same optimization.
>> (A9 maybe, A17 probably, some recent 64-bit cores)
>>
>> Are there software work-arounds for Spectre planned for arm32 and arm64?
> 
> Yes, I think they are currently buried in one of the arm64 trees, and
> they have been posted to the mailing list a few times in the past.

Found the burial ground, thanks Greg.

  https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=kpti

Via https://developer.arm.com/support/security-update

"For Cortex-R8, Cortex-A8, Cortex-A9, and Cortex-A17, invalidate
the branch predictor using a BPIALL instruction."

The latest arm32 patch series was submitted recently:

  https://www.spinics.net/lists/arm-kernel/msg630892.html

Regards.