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

[Dave Hansen]

On 01/27/2018 05:42 AM, Konrad Rzeszutek Wilk wrote:
> On Fri, Jan 26, 2018 at 07:11:47PM +0000, Hansen, Dave wrote:
>> The need for RSB stuffing in all the various scenarios and what the heck it actually mitigates is freakishly complicated.  I've tried to write it all down in one place: https://goo.gl/pXbvBE
> Thank you for sharing that.
> 
> One question on the third from the top (' RSB Stuff (16) After
> irq/nmi/#PF/...').
> 
> It says that :"Return from interrupt path (more than 16 deep) can empty
> RSB".
> 
> Just to clarify - you mean all the returns ('ret') that are happening after
> we call do_IRQ and the stack unwinds - but before we do an 'iret' correct?

Correct.  The RSB is not used or updated by iret.