Re: [PATCH 2/2] x86/bugs: Don't fill RSB on context switch with eIBRS

[Pawan Gupta]

On Tue, Nov 19, 2024 at 11:27:51PM -0800, Josh Poimboeuf wrote:
> User->user Spectre v2 attacks (including RSB) across context switches
> are already mitigated by IBPB in cond_mitigation(), if enabled globally
> or if at least one of the tasks has opted in to protection.  RSB filling

Is below less ambiguous?

s/if at least one of the tasks/if previous or the next task/

> without IBPB serves no purpose for protecting user space, as indirect
> branches are still vulnerable.
> 
> User->kernel RSB attacks are mitigated by eIBRS.  In which case the RSB
> filling on context switch isn't needed.  Fix that.
> 
> While at it, update and coalesce the comments describing the various RSB
> mitigations.
> 
> Suggested-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

Reviewed-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>