Messages in this thread | | | From | KP Singh <> | Date | Sat, 25 Feb 2023 20:42:35 -0500 | Subject | Re: [PATCH v2 2/2] Documentation/hw-vuln: Document the interaction between IBRS and STIBP |
| |
On Thu, Feb 23, 2023 at 9:52 AM Borislav Petkov <bp@alien8.de> wrote: > > On Tue, Feb 21, 2023 at 07:49:08PM +0100, KP Singh wrote: > > ... Consequently, STIBP needs to be explicitly > > + enabled to guard against cross-thread attacks in userspace. > > needs? > > That sounds like something the user needs to do. But we do it by > default. Let's rephrase: > > "Systems which support enhanced IBRS (eIBRS) enable IBRS protections once at > boot and they're automatically protected against Spectre v2 variant > attacks, including cross-thread branch target injections on SMT systems > (STIBP). IOW, eIBRS enables STIBP too. > > Legacy IBRS systems clear the IBRS bit on exit to userspace and > therefore explicitly enable STIBP for that."
+ Systems which support enhanced IBRS (eIBRS) enable IBRS protection once at + boot, by setting the IBRS bit, and they're automatically protected against + Spectre v2 variant attacks, including cross-thread branch target injections + on SMT systems (STIBP). In other words, eIBRS enables STIBP too. + + Legacy IBRS systems clear the IBRS bit on exit to userspace and + therefore explicitly enable STIBP for that
I did add one phrase, we really need to stress on the IBRS bit here. Had we been enabling KERNEL_IBRS accidentally with eIBRS, it would still mess things up as the bit being set is important.
This is why my original patch felt "obtuse" as it focused on KERNEL_IBRS instead of IBRS or eIBRS :).
> > Simple. > > -- > Regards/Gruss, > Boris. > > https://people.kernel.org/tglx/notes-about-netiquette
| |