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

From	Borislav Petkov <bp@suse.de>
Newsgroups	linux.kernel
Subject	Re: [v6 PATCH 07/21] x86/insn-eval: Add utility function to get segment descriptor
Date	2017-05-04 13:10 +0200
Message-ID	<tDmNX-2Ds-3@gated-at.bofh.it> (permalink)
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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?

Thanks.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--

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Re: [v6 PATCH 07/21] x86/insn-eval: Add utility function to get  segment descriptor Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-04-27 00:00 +0200
  Re: [v6 PATCH 07/21] x86/insn-eval: Add utility function to get  segment descriptor Borislav Petkov <bp@suse.de> - 2017-05-04 13:10 +0200

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