Re: [PATCH v3 7/7] x86/ldt,ptrace: provide regset access to the LDT

[Andy Lutomirski]

On Fri, Jun 22, 2018 at 8:06 AM <hpa@xxxxxxxxx> wrote:
>
> On June 22, 2018 7:49:13 AM PDT, Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> >On Thu, Jun 21, 2018 at 2:18 PM H. Peter Anvin, Intel
> ><h.peter.anvin@xxxxxxxxx> wrote:
> >>
> >> From: "H. Peter Anvin" <hpa@xxxxxxxxxxxxxxx>
> >>
> >> Provide ptrace/regset access to the LDT, if one exists.  This
> >> interface provides both read and write access. The write code is
> >> unified with modify_ldt(); the read code doesn't have enough
> >> similarity so it has been kept made separate.
> >
> >For this and for the GDT, you've chosen to use struct user_desc as
> >your format instead of using a native hardware descriptor format.  Any
> >particular reason why?  If nothing else, it will bloat core files a
> >bit more than needed.
>
> I did because REGSET_TLS was implemented that way, and that is simply a subset of the GDT (which made the same code trivially applicable to both.) modify_ldt() does it *both* ways for extra fun (one for reading, and one for writing.)
>
> ->active is defined as "beyond this point the regset contains only the default value", which seemed appropriate in this case.

I saw that definition too.  But I'm still very unclear as to what, if
anything, the code actually does :)

--Andy