linux-kernel - Re: [PATCHv8 14/17] x86/traps: Handle LASS thrown #SS

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Message-ID: <29992EA3-8BEE-4B31-A38F-F3E65FA9609D@zytor.com>
Date: Sun, 06 Jul 2025 08:07:11 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: David Laight <david.laight.linux@...il.com>
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Subject: Re: [PATCHv8 14/17] x86/traps: Handle LASS thrown #SS

On July 6, 2025 2:22:13 AM PDT, David Laight <david.laight.linux@...il.com> wrote:
>On Tue, 01 Jul 2025 19:06:10 -0700
>"H. Peter Anvin" <hpa@...or.com> wrote:
>...
>> Note: for a FRED system, ERETU can generate #SS for a non-canonical user space
>> RSP even in the absence of LASS, so if that is not currently handled that is an active bug.
>
>Is that a fault in kernel space, or a fault in user space. 
>
>Some of the traps for 'iret' happen after the transition to user space,
>so the kernel doesn't have to handle them as special cases.
>(I simplified (and fixed) one version of that code.)
>
>	David
>

It's a fault in user space. I had a brain fart and managed to forget that RSP is technically a GPR and as such is not limited to the VA width of the machine.