RE: [PATCH] x86/ia32: Do not modify the DPL bits for a null selector

[Li, Xin3]

> > It bothers me that the existing code, and your code as well only
> > handles the normalization on x86_64 for ia32 mode.  Shouldn't the same
> > normalization logic apply in a 32bit kernel as well?
> > Scope creep I know but the fact the code does not match seems
> > concerning.
> 
> Agreed! We *should* fix it in the same way.

The fact is that the existing code unconditionally sets the DPL bits
to 3 only on x86_64 (why did we forgot to do it on 32-bit?). Thus,
there is nothing to revert for null selectors on 32-bit.

With your suggestion to normalize null selectors, we need to add the
code only when IRET is NOT used to return to user level. Fortunately,
Brian Gerst just posted a patch set
https://lore.kernel.org/lkml/20230721161018.50214-1-brgerst@xxxxxxxxx/,
which makes the case whether IRET is used or not explicit on both x86_64
and x86_32. As a result it is straightforward to add the normalization
code afterwards.

Thanks!
  Xin