RE: [PATCH for-4.14] x86/spec-ctrl: Protect against CALL/JMP straight-line speculation

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 01 July 2020 13:27
> To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Roger 
> Pau Monné
> <roger.pau@xxxxxxxxxx>; Paul Durrant <paul@xxxxxxx>
> Subject: Re: [PATCH for-4.14] x86/spec-ctrl: Protect against CALL/JMP 
> straight-line speculation
> 
> On 01.07.2020 13:58, Andrew Cooper wrote:
> > Some x86 CPUs speculatively execute beyond indirect CALL/JMP instructions.
> >
> > With CONFIG_INDIRECT_THUNK / Retpolines, indirect CALL/JMP instructions are
> > converted to direct CALL/JMP's to __x86_indirect_thunk_REG(), leaving just a
> > handful of indirect JMPs implementing those stubs.
> >
> > There is no architectrual execution beyond an indirect JMP, so use INT3 as
> > recommended by vendors to halt speculative execution.  This is shorter than
> > LFENCE (which would also work fine), but also shows up in logs if we do
> > unexpected execute them.
> >
> > Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Release-acked-by: Paul Durrant <paul@xxxxxxx>