feat(gcs): support guarded control stack
Arm v9.4 introduces support for Guarded Control Stack, providing
mitigations against some forms of RPO attacks and an efficient mechanism
for obtaining the current call stack without requiring a full stack
unwind. Enable access to this feature for EL2 and below, context
switching the newly added EL2 registers as appropriate.
Change the FVP platform to default to handling this as a dynamic option
so the right decision can be made by the code at runtime.
Signed-off-by: Mark Brown <broonie@kernel.org>
Change-Id: I691aa7c22e3547bb3abe98d96993baf18c5f0e7b
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 03be786..d2f463f 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -374,6 +374,12 @@
can take the values 0 to 2, to align with the ``FEATURE_DETECTION``
mechanism. Default value is ``0``.
+- ``ENABLE_FEAT_GCS``: Numeric value to set the bit SCR_EL3.GCSEn in EL3 to
+ allow use of Guarded Control Stack from EL2 as well as adding the GCS
+ registers to the EL2 context save/restore operations. This flag can take
+ the values 0 to 2, to align with the ``FEATURE_DETECTION`` mechanism.
+ Default value is ``0``.
+
- ``ENABLE_LTO``: Boolean option to enable Link Time Optimization (LTO)
support in GCC for TF-A. This option is currently only supported for
AArch64. Default is 0.