svn commit: r327876 - in head/sys/arm64: arm64 include

[Warner Losh]

On Fri, Jan 12, 2018 at 7:52 AM, Andrew Turner <andrew at freebsd.org> wrote:

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> On 12 Jan 2018, at 14:37, Warner Losh <imp at bsdimp.com> wrote:
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> On Fri, Jan 12, 2018 at 7:15 AM, Andrew Turner <andrew at freebsd.org> wrote:
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>> On 12 Jan 2018, at 14:10, Marcin Wojtas <mw at semihalf.com> wrote:
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>> Hi Andrew,
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>>
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>> 2018-01-12 15:01 GMT+01:00 Andrew Turner <andrew at freebsd.org>:
>>
>> Author: andrew
>> Date: Fri Jan 12 14:01:38 2018
>> New Revision: 327876
>> URL: https://svnweb.freebsd.org/changeset/base/327876
>>
>> Log:
>>  Workaround Spectre Variant 2 on arm64.
>>
>>  We need to handle two cases:
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>>  1. One process attacking another process.
>>  2. A process attacking the kernel.
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>>  For the first case we clear the branch predictor state on context switch
>>  between different processes. For the second we do this when taking an
>>  instruction abort on a non-userspace address.
>>
>>  To clear the branch predictor state a per-CPU function pointer has been
>>  added. This is set by the new cpu errata code based on if the CPU is
>>  known to be affected.
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>>  On Cortex-A57, A72, A73, and A75 we call into the PSCI firmware as newer
>>  versions of this will clear the branch predictor state for us.
>>
>>  It has been reported the ThunderX is unaffected, however the ThunderX2 is
>>  vulnerable. The Qualcomm Falkor core is also affected. As FreeBSD doesn't
>>  yet run on the ThunderX2 or Falkor no workaround is included for these
>> CPUs.
>>
>>
>> Regardless ThunderX2 / Falkor work-arounds, do I understand correctly
>> that pure CA72 machines, such as Marvell Armada 7k/8k are immune to
>> Variant 2 now?
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>>
>> It is my understanding that the A72 will be immune with this patch and an
>> updated Arm Trusted Firmware as documented in [1].
>>
>> Andrew
>>
>> [1] https://github.com/ARM-software/arm-trusted-firmware/wik
>> i/ARM-Trusted-Firmware-Security-Advisory-TFV-6
>>
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> Are you also working on aarch32 mitigation?
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>
> No. I think a similar technique could be used, however as aarch32 has
> instructions to invalidate the branch predictor these can be used directly.
>

That's my reading as well. It looks fairly easy to do it always, but I've
not researched it sufficiently.

Warner