Re: [v6 PATCH 07/21] x86/insn-eval: Add utility function to get segment descriptor

[Ricardo Neri]

On Thu, 2017-05-04 at 13:02 +0200, Borislav Petkov wrote:
> On Wed, Apr 26, 2017 at 02:51:56PM -0700, Ricardo Neri wrote:
> > > > +			     seg >= current->active_mm->context.ldt->size)) {
> > > 
> > > ldt->size is the size of the descriptor table but you've shifted seg by
> > > 3. That selector index is shifted by 3 (to the left) to form an offset
> > > into the descriptor table because the entries there are 8 bytes.
> > 
> > I double-checked the ldt code and it seems to me that size refers to the
> > number of entries in the table; it is always multiplied by
> > LDT_ENTRY_SIZE [1], [2]. Am I missing something?
> 
> No, you're not. I fell into that wrongly named struct member trap.
> 
> So ldt_struct.size should actually be called ldt_struct.n_entries or
> similar. Because what's in there is now is not "size".
> 
> And then code like
> 
> 	new_ldt->size * LDT_ENTRY_SIZE
> 
> would make much more sense if written like this:
> 
> 	new_ldt->n_entries * LDT_ENTRY_SIZE
> 
> Would you fix that in a prepatch pls?
> 

Sure I can. Would this trigger a v8 of my series? I was hoping v7 series
could be merged and then start doing incremental work on top of it. Does
it make sense?

Thanks and BR,
Ricardo