Re: [PATCH v3 10/13] x86/retpoline/pvops: Convert assembler indirect jumps

[Andrew Cooper]

On 04/01/18 15:02, Juergen Gross wrote:
> On 04/01/18 15:37, David Woodhouse wrote:
>> Convert pvops invocations to use non-speculative call sequences, when
>> CONFIG_RETPOLINE is enabled.
>>
>> There is scope for future optimisation here â once the pvops methods are
>> actually set, we could just turn the damn things into *direct* jumps.
>> But this is perfectly sufficient for now, without that added complexity.
> I don't see the need to modify the pvops calls.
>
> All indirect calls are replaced by either direct calls or other code
> long before any user code is active.
>
> For modules the replacements are in place before the module is being
> used.

When booting virtualised, sibling hyperthreads can arrange VM-to-VM SP2
attacks.

One mitigation though is to consider if there is any interesting data to
leak that early during boot.

~Andrew