New subject: BRANCH_PROTECTION

13 Apr 2020


      Hi Varun,
1.  The value of '1' sets ‘standard’ type of BP which according to GCC documentation:
"turns on all types of branch protection features. If a feature has additional tuning options, then ‘standard’ sets it to its standard level. "
It equals to "bti+pac-ret".
  2.  Yes. See above and use option value of '1'.
Regards.
Alexei
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From: TF-A tf-a-bounces@lists.trustedfirmware.org on behalf of Varun Wadekar via TF-A tf-a@lists.trustedfirmware.org
Sent: 10 April 2020 19:28
To: tf-a@lists.trustedfirmware.org tf-a@lists.trustedfirmware.org
Cc: Kalyani Chidambaram Vaidyanathan kalyanic@nvidia.com; Anthony Zhou anzhou@nvidia.com
Subject: Re: [TF-A] BRANCH_PROTECTION
Hello,
Can someone please help clarify?
-Varun
From: TF-A tf-a-bounces@lists.trustedfirmware.org On Behalf Of Varun Wadekar via TF-A
Sent: Tuesday, April 7, 2020 9:58 PM
To: tf-a@lists.trustedfirmware.org
Cc: Kalyani Chidambaram Vaidyanathan kalyanic@nvidia.com; Anthony Zhou anzhou@nvidia.com
Subject: [TF-A] BRANCH_PROTECTION
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Hello,
Can someone please help me understand if
1.  a ‘value’ of ‘1’ for BRANCH_PROTECTION covers the PAuth protection provided by a value of ‘2’ and/or ‘3’?
  2.  there is a way to enable BTI and “pac-ret” at the same time?
The docs provide this information.
<snip>
-  ``BRANCH_PROTECTION``: Numeric value to enable ARMv8.3 Pointer Authentication
and ARMv8.5 Branch Target Identification support for TF-A BL images themselves.
If enabled, it is needed to use a compiler that supports the option
``-mbranch-protection``. Selects the branch protection features to use:
-  0: Default value turns off all types of branch protection
-  1: Enables all types of branch protection features
-  2: Return address signing to its standard level
-  3: Extend the signing to include leaf functions
The table below summarizes ``BRANCH_PROTECTION`` values, GCC compilation options
and resulting PAuth/BTIhttps://tegra-sw-opengrok.nvidia.com/source/s?path=PAuth/BTI&project=stage-main_automotive features.
+-------+--------------+-------+-----+
| Value |  GCC option  | PAuth | BTI |
+=======+==============+=======+=====+
|   0   |     none     |   N   |  N  |
+-------+--------------+-------+-----+
|   1   |   standard   |   Y   |  Y  |
+-------+--------------+-------+-----+
|   2   |   pac-ret    |   Y   |  N  |
+-------+--------------+-------+-----+
|   3   | pac-ret+leaf |   Y   |  N  |
+-------+--------------+-------+-----+
This option defaults to 0 and this is an experimental feature.
Note that Pointer Authentication is enabled for Non-secure world
irrespective of the value of this option if the CPU supports it.
<snip>
Thanks,
Varun
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