Re: [PATCH v2 1/2] retpolines: Only enable retpoline support when compiler support it

[Ingo Molnar]

* Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:

> On Thu, 1 Nov 2018, Woodhouse, David wrote:
> > On Thu, 2018-11-01 at 10:50 +0100, Ingo Molnar wrote:
> > > * Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx> wrote:
> > > 
> > > > Since retpoline capable compilers are widely available, make
> > > > CONFIG_RETPOLINE hard depend on it.
> > > > 
> > > > The check of RETPOLINE is changed to CONFIG_RETPOLINE.
> > > > 
> > > > This change is based on suggestion in https://lkml.org/lkml/2018/9/18/1016
> > > > 
> > > > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
> > > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > > 
> > > Please turn such 'based on suggestions' into proper tags as well, i.e. 
> > > something like:
> > > 
> > >   Suggested-by: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> > 
> > I think the suggestion came from PeterZ; I just acked it.
> > 
> > Although on furthe reflection, I think I'd prefer a build break if
> > retpoline is enabled in the kernel config and the compiler doesn't
> > support it. This patch would make it silently fail to be secure.
> 
> Agreed.

Yeah, I agree that that's the best policy: if someone wants retpoline 
support it shouldn't silently turn off just because the wrong toolchain 
was used to build the kernel ...

Thanks,

	Ingo