linux-kernel - Re: [PATCH v9 23/42] Documentation/x86: Add CET shadow stack description

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Message-ID: <a7f312b1e712b87f4932d6295e6f6d28f41afd8f.camel@intel.com>
Date:   Thu, 6 Jul 2023 16:59:45 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [PATCH v9 23/42] Documentation/x86: Add CET shadow stack
 description

On Thu, 2023-07-06 at 15:24 +0100, Mark Brown wrote:
> On Thu, Jul 06, 2023 at 02:14:40PM +0100,
> szabolcs.nagy@....com wrote:
> > The 07/05/2023 20:29, Mark Brown wrote:
> 
> > > Push and pop are one control, you get both or neither.
> 
> > gcspopm is always available (esentially *ssp++, this is used
> > for longjmp).
> 
> Ah, sorry - I misremembered there.  You're right, it's only push that
> we
> have control over.

Ah, ok! So if you are not planning to enable the push mode then the
features are pretty well aligned, except:
 - On x86 it is possible to switch stacks without leaving a token 
   behind.
 - The GCSPOPM/INCSSP looping may require longer loops on ARM 
   because it only pops one at at time.

If you are not going to use GCSPUSHM by default, then I think we
*should* be able to have some unified set of rules for developers for
glibc behaviors at least.