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Re: [PATCH 14/16] x86/alt: Adjust _alternative_instructions() to not create shadow stacks

To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
From: Jan Beulich <jbeulich@xxxxxxxx>
Date: Thu, 7 May 2020 15:49:19 +0200
Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
Delivery-date: Thu, 07 May 2020 13:49:24 +0000
List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 02.05.2020 00:58, Andrew Cooper wrote:
> The current alternatives algorithm clears CR0.WP and writes into .text.  This
> has a side effect of the mappings becoming shadow stacks once CET is active.
> 
> Adjust _alternative_instructions() to clean up after itself.  This involves
> extending the set of bits modify_xen_mappings() to include Dirty (and Accessed
> for good measure).
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

References:
- [PATCH 00/16] x86: Support for CET Supervisor Shadow Stacks
  - From: Andrew Cooper
- [PATCH 14/16] x86/alt: Adjust _alternative_instructions() to not create shadow stacks
  - From: Andrew Cooper

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