target/arm: Catch illegal-exception-return from EL3 with bad NSE/NS
The architecture requires (R_TYTWB) that an attempt to return from EL3
when SCR_EL3.{NSE,NS} are {1,0} is an illegal exception return. (This
enforces that the CPU can't ever be executing below EL3 with the
NSE,NS bits indicating an invalid security state.)
We were missing this check; add it.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230807150618.101357-1-peter.maydell@linaro.org
diff --git a/target/arm/tcg/helper-a64.c b/target/arm/tcg/helper-a64.c
index 1c9370f..0cf56f6 100644
--- a/target/arm/tcg/helper-a64.c
+++ b/target/arm/tcg/helper-a64.c
@@ -780,6 +780,15 @@
spsr &= ~PSTATE_SS;
}
+ /*
+ * FEAT_RME forbids return from EL3 with an invalid security state.
+ * We don't need an explicit check for FEAT_RME here because we enforce
+ * in scr_write() that you can't set the NSE bit without it.
+ */
+ if (cur_el == 3 && (env->cp15.scr_el3 & (SCR_NS | SCR_NSE)) == SCR_NSE) {
+ goto illegal_return;
+ }
+
new_el = el_from_spsr(spsr);
if (new_el == -1) {
goto illegal_return;
