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SubjectRe: [PATCH v8 31/33] x86/fred: BUG() when ERETU with %rsp not equal to that when the ring 3 event was just delivered
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On 6/5/23 07:15, Thomas Gleixner wrote:
> On Mon, Apr 10 2023 at 01:14, Xin Li wrote:
>> A FRED stack frame generated by a ring 3 event should never be messed up, and
>> the first thing we must make sure is that at the time an ERETU instruction is
>> executed, %rsp must have the same address as that when the user level event
>> was just delivered.
>>
>> However we don't want to bother the normal code path of ERETU because it's on
>> the hotest code path, a good choice is to do this check when ERETU
>> faults.
>
> Which might be not catching bugs where the wrong frame makes ERETU not
> fault.
>
> We have CONFIG_DEBUG_ENTRY for catching this at the proper place.
>

This is true, but this BUG() is a cheap test on a slow path, and thus
can be included in production code.

-hpa

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