Re: [PATCH tip v8] x86/setup: Use rng seeds from setup_data

[H. Peter Anvin]

On 7/9/22 14:57, Borislav Petkov wrote:
> On Sat, Jul 09, 2022 at 02:45:24PM -0700, H. Peter Anvin wrote:
> > On 7/9/22 02:49, Borislav Petkov wrote:
> > > On Fri, Jul 08, 2022 at 06:51:16PM -0700, H. Peter Anvin wrote:
> > > > #define SETUP_ENUM_MAX	SETUP_RNG_SEED
> > > > #define SETUP_INDIRECT	(1<<31)
> > > > #define SETUP_TYPE_MAX	(SETUP_ENUM_MAX | SETUP_INDIRECT)
> > >
> > > Wait, if we get to add a new number, SETUP_ENUM_MAX and thus
> > > SETUP_TYPE_MAX will change. And they're uapi too...
> >
> > Talking API here rather than ABI, i.e. the semantics of those symbols.
>
> Sure but do we worry about some userspace including those headers and
> relying on the SETUP_ENUM_MAX number?
>
> Or is userspace required to be recompiled against newer uapi headers?

In ABI/API terms, that symbol has the semantic of connecting the API 
version to the underlying ABI version; a piece of code that sees an 
enumeration type > SETUP_ENUM_MAX must by definition treat it as an 
opaque blob. In the future, should it become warranted, we may add flags 
that indicate how unaware code should handle them, but I don't think we 
can engineer that right now.

	-hpa