Re: [PATCH RESEND] x86/speculation: Fix user-mode spectre-v2 protection with KERNEL_IBRS

On Mon, Feb 20, 2023 at 10:01:57AM -0800, KP Singh wrote:

Well, we disable IBRS userspace (this is KENREL_IBRS), because it is slow. Now if a user space process wants to protect itself from cross thread training, it should be able to do it, either by turning STIBP always on or using a prctl to enable. With the current logic, it's unable to do so.

Ofcourse it can:

[SPECTRE_V2_USER_PRCTL] = "User space: Mitigation: STIBP via prctl",

we did this at the time so that a userspace process can control it via prctl().

So, maybe you should explain what you're trying to accomplish in detail and where it fails...