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

KP Singh
2023-02-20T19:12:54Z

On Mon, Feb 20, 2023 at 11:02 AM Borislav Petkov <bp@alien8.de> wrote:
>
> On Mon, Feb 20, 2023 at 10:56:38AM -0800, KP Singh wrote:
> > Sure, it looks like an omission to me, we wrote a POC on Skylake that
> > was able to do cross-thread training with the current set of
> > mitigations.
>
> Right.
>
> > STIBP with IBRS is still correct if spectre_v2=ibrs had really meant
> > IBRS everywhere,
>
> Yeah, IBRS everywhere got shot down as a no-no very early in the game,
> for apparent reasons.

As you said in the other thread, this needs to be documented both in
the code and the kernel documentation.

>
> > but just means KERNEL_IBRS, which means only kernel is protected,
> > userspace is still unprotected.
>
> Yes, that was always the intent with IBRS: enable on kernel entry and
> disable on exit.
>
> Thx.
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette