fix(el3-runtime): set unset pstate bits to default
During a transition to a higher EL some of the PSTATE bits are not set
by hardware, this means that their state may be leaked from lower ELs.
This patch sets those bits to a default value upon entry to EL3.
This patch was tested using a debugger to check the PSTATE values
are correctly set. As well as adding a test in the next patch to
ensure the PSTATE in lower ELs is still maintained after this change.
Change-Id: Ie546acbca7b9aa3c86bd68185edded91b2a64ae5
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
diff --git a/lib/el3_runtime/aarch64/context.S b/lib/el3_runtime/aarch64/context.S
index bea72c8..c1c0612 100644
--- a/lib/el3_runtime/aarch64/context.S
+++ b/lib/el3_runtime/aarch64/context.S
@@ -682,6 +682,22 @@
endfunc fpregs_context_restore
#endif /* CTX_INCLUDE_FPREGS */
+ /*
+ * Set the PSTATE bits not set when the exception was taken as
+ * described in the AArch64.TakeException() pseudocode function
+ * in ARM DDI 0487F.c page J1-7635 to a default value.
+ */
+ .macro set_unset_pstate_bits
+ /*
+ * If Data Independent Timing (DIT) functionality is implemented,
+ * always enable DIT in EL3
+ */
+#if ENABLE_FEAT_DIT
+ mov x8, #DIT_BIT
+ msr DIT, x8
+#endif /* ENABLE_FEAT_DIT */
+ .endm /* set_unset_pstate_bits */
+
/* ------------------------------------------------------------------
* The following macro is used to save and restore all the general
* purpose and ARMv8.3-PAuth (if enabled) registers.
@@ -767,17 +783,26 @@
stp x26, x27, [x19, #CTX_PACDBKEY_LO]
stp x28, x29, [x19, #CTX_PACGAKEY_LO]
#endif /* CTX_INCLUDE_PAUTH_REGS */
-
.endm /* save_gp_pmcr_pauth_regs */
/* -----------------------------------------------------------------
- * This function saves the context preparing entry to el3.
+ * This function saves the context and sets the PSTATE to a known
+ * state, preparing entry to el3.
* Save all the general purpose and ARMv8.3-PAuth (if enabled)
* registers.
+ * Then set any of the PSTATE bits that are not set by hardware
+ * according to the Aarch64.TakeException pseudocode in the Arm
+ * Architecture Reference Manual to a default value for EL3.
+ * clobbers: x17
* -----------------------------------------------------------------
*/
func prepare_el3_entry
save_gp_pmcr_pauth_regs
+ /*
+ * Set the PSTATE bits not described in the Aarch64.TakeException
+ * pseudocode to their default values.
+ */
+ set_unset_pstate_bits
ret
endfunc prepare_el3_entry