Re: [PATCH 4/7] x86: Add support for rd/wr fs/gs base

[H. Peter Anvin]

On 05/01/2014 03:18 PM, Andi Kleen wrote:
>> I haven't looked through the flows (I'm at LCE so I have limited screen
>> bandwidth) to see how that would be handled in this case, but in the
>> general paranoid case it comes down to the fact that in this particular
>> subcase we don't necessarily know exactly how many SWAPGS are between us
>> and userspace after we IRET.
> 
> There is none as far as I know. Certainly wasn't any when the code
> was originally written.
> 

This applies for an asynchronous entry from kernel space.  Obviously in
the case where we actually come directly from user space (the stack
frame CS.RPL == 3) then that doesn't apply.

	-hpa


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