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

Borislav Petkov
2023-02-20T18:22:28Z

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...

--
Regards/Gruss,
Boris.