From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and
 pmdp_set_wrprotect for _PAGE_DIRTY_SW
Date: Thu, 30 Aug 2018 10:33:34 -0700
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To: Yu-cheng Yu <yu-cheng.yu@intel.com>, Jann Horn <jannh@google.com>
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On 08/30/2018 10:26 AM, Yu-cheng Yu wrote:
> We don't have the guard page now, but there is a shadow stack token
> there, which cannot be used as a return address.

The overall concern is that we could overflow into a page that we did
not intend.  Either another actual shadow stack or something that a page
that the attacker constructed, like the transient scenario Jann described.