target/arm: v8M: Check state of exception being returned from

In v8M, an attempt to return from an exception which is not
active is an illegal exception return. For this purpose,
exceptions which can configurably target either Secure or
NonSecure are not considered to be active if they are
configured for the opposite security state for the one
we're trying to return from (eg attempt to return from
an NS NMI but NMI targets Secure). In the pseudocode this
is handled by IsActiveForState().

Detect this case rather than counting an active exception
possibly of the wrong security state as being sufficient.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190617175317.27557-4-peter.maydell@linaro.org

1 files changed, 13 insertions, 1 deletions

diff --git a/hw/intc/armv7m_nvic.c b/hw/intc/armv7m_nvic.c
index 330eb728dd..9f8f0d3ff5 100644
--- a/hw/intc/armv7m_nvic.c
+++ b/hw/intc/armv7m_nvic.c
@@ -860,7 +860,19 @@ int armv7m_nvic_complete_irq(void *opaque, int irq, bool secure)
         return -1;
     }
 
-    ret = nvic_rettobase(s);
+    /*
+     * If this is a configurable exception and it is currently
+     * targeting the opposite security state from the one we're trying
+     * to complete it for, this counts as an illegal exception return.
+     * We still need to deactivate whatever vector the logic above has
+     * selected, though, as it might not be the same as the one for the
+     * requested exception number.
+     */
+    if (!exc_is_banked(irq) && exc_targets_secure(s, irq) != secure) {
+        ret = -1;
+    } else {
+        ret = nvic_rettobase(s);
+    }
 
     vec->active = 0;
     if (vec->level) {