fusee/exo: add ability to disable user exception handlers

please do not use this
yellows8 needs it to debug am, 99% of use cases want them on

common/defaults/BCT.ini

@@ -8,6 +8,9 @@ stage2_entrypoint = 0xF0000000
 ; Note: Disabling debugmode will cause parts of ams.tma to not work, in the future.
 debugmode = 1 
 debugmode_user = 0
+; Note: Disabling usermode exception handlers will cause atmosphere to not fail gracefully under error conditions.
+; Support will not be provided to users who disable these. If you do not know what you are doing, leave them on.
+disable_user_exception_handlers = 0
 
 [stratosphere]
 ; To force-enable nogc, add nogc = 1

exosphere/src/configitem.c

@@ -37,6 +37,7 @@
 
 static bool g_hiz_mode_enabled = false;
 static bool g_debugmode_override_user = false, g_debugmode_override_priv = false;
+static bool g_enable_usermode_exception_handlers = true;
 
 uint32_t configitem_set(bool privileged, ConfigItem item, uint64_t value) {
     switch (item) {
@@ -163,6 +164,10 @@ void configitem_set_debugmode_override(bool user, bool priv) {
     g_debugmode_override_priv = priv;
 }
 
+void configitem_disable_usermode_exception_handlers(void) {
+    g_enable_usermode_exception_handlers = false;
+}
+
 uint32_t configitem_get(bool privileged, ConfigItem item, uint64_t *p_outvalue) {
     uint32_t result = 0;
     switch (item) {
@@ -213,8 +218,10 @@ uint32_t configitem_get(bool privileged, ConfigItem item, uint64_t *p_outvalue)
         case CONFIGITEM_KERNELCONFIGURATION:
             {
                 uint64_t config = bootconfig_get_kernel_configuration();
-                /* Always enable usermode exception handlers. */
+                /* Enable usermode exception handlers by default. */
+                if (g_enable_usermode_exception_handlers) {
                     config |= KERNELCONFIGFLAG_ENABLE_USER_EXCEPTION_HANDLERS;
+                }
                 *p_outvalue = config;
             }
             break;

exosphere/src/configitem.h

@@ -60,6 +60,7 @@ bool configitem_is_hiz_mode_enabled(void);
 bool configitem_is_debugmode_priv(void);
 
 void configitem_set_debugmode_override(bool user, bool priv);
+void configitem_disable_usermode_exception_handlers(void);
 void configitem_set_hiz_mode_enabled(bool enabled);
 
 uint64_t configitem_get_hardware_type(void);

exosphere/src/exocfg.c

@@ -75,3 +75,11 @@ unsigned int exosphere_should_override_debugmode_user(void) {
     
     return EXOSPHERE_CHECK_FLAG(EXOSPHERE_FLAG_IS_DEBUGMODE_USER);
 }
+
+unsigned int exosphere_should_disable_usermode_exception_handlers(void) {
+    if (!g_has_loaded_config) {
+        generic_panic();
+    }
+    
+    return EXOSPHERE_CHECK_FLAG(EXOSPHERE_FLAG_DISABLE_USERMODE_EXCEPTION_HANDLERS);
+}

exosphere/src/exocfg.h

@@ -35,10 +35,11 @@
 /* Exosphere config in DRAM shares physical/virtual mapping. */
 #define MAILBOX_EXOSPHERE_CONFIG_PHYS MAILBOX_EXOSPHERE_CONFIG
 
-#define EXOSPHERE_FLAGS_DEFAULT 0x00000000
 #define EXOSPHERE_FLAG_PERFORM_620_KEYGEN                   (1 << 0u)
 #define EXOSPHERE_FLAG_IS_DEBUGMODE_PRIV                    (1 << 1u)
 #define EXOSPHERE_FLAG_IS_DEBUGMODE_USER                    (1 << 2u)
+#define EXOSPHERE_FLAG_DISABLE_USERMODE_EXCEPTION_HANDLERS  (1 << 3u)
+#define EXOSPHERE_FLAGS_DEFAULT (EXOSPHERE_FLAG_IS_DEBUGMODE_PRIV)
 
 typedef struct {
     unsigned int magic;
@@ -52,6 +53,7 @@ unsigned int exosphere_get_target_firmware(void);
 unsigned int exosphere_should_perform_620_keygen(void);
 unsigned int exosphere_should_override_debugmode_priv(void);
 unsigned int exosphere_should_override_debugmode_user(void);
+unsigned int exosphere_should_disable_usermode_exception_handlers(void);
 
 static inline unsigned int exosphere_get_target_firmware_for_init(void) {
     const unsigned int magic = MAILBOX_EXOSPHERE_CONFIG_PHYS.magic;

exosphere/src/package2.c

@@ -538,6 +538,9 @@ void load_package2(coldboot_crt0_reloc_list_t *reloc_list) {
     /* Load Exosphere-specific config. */
     exosphere_load_config();
     configitem_set_debugmode_override(exosphere_should_override_debugmode_user() != 0, exosphere_should_override_debugmode_priv() != 0);
+    if (exosphere_should_disable_usermode_exception_handlers() != 0) {
+        configitem_disable_usermode_exception_handlers();
+    }
 
     /* Setup the Security Engine. */
     setup_se();

fusee/fusee-secondary/src/exocfg.h

@@ -24,10 +24,11 @@
 /* "EXO0" */
 #define MAGIC_EXOSPHERE_CONFIG (0x304F5845)
 
-#define EXOSPHERE_FLAGS_DEFAULT 0x00000000
 #define EXOSPHERE_FLAG_PERFORM_620_KEYGEN                   (1 << 0u)
 #define EXOSPHERE_FLAG_IS_DEBUGMODE_PRIV                    (1 << 1u)
 #define EXOSPHERE_FLAG_IS_DEBUGMODE_USER                    (1 << 2u)
+#define EXOSPHERE_FLAG_DISABLE_USERMODE_EXCEPTION_HANDLERS  (1 << 3u)
+#define EXOSPHERE_FLAGS_DEFAULT (EXOSPHERE_FLAG_IS_DEBUGMODE_PRIV)
 
 typedef struct {
     unsigned int magic;
@@ -41,5 +42,6 @@ typedef struct {
 #define EXOSPHERE_TARGETFW_KEY "target_firmware"
 #define EXOSPHERE_DEBUGMODE_PRIV_KEY "debugmode"
 #define EXOSPHERE_DEBUGMODE_USER_KEY "debugmode_user"
+#define EXOSPHERE_DISABLE_USERMODE_EXCEPTION_HANDLERS_KEY "disable_user_exception_handlers"
 
 #endif

fusee/fusee-secondary/src/nxboot.c

@@ -106,22 +106,27 @@ static int exosphere_ini_handler(void *user, const char *section, const char *na
     if (strcmp(section, "exosphere") == 0) {
         if (strcmp(name, EXOSPHERE_TARGETFW_KEY) == 0) {
             sscanf(value, "%d", &exo_cfg->target_firmware);
-        } 
+        } else if (strcmp(name, EXOSPHERE_DEBUGMODE_PRIV_KEY) == 0) {
-        if (strcmp(name, EXOSPHERE_DEBUGMODE_PRIV_KEY) == 0) {
             sscanf(value, "%d", &tmp);
             if (tmp) {
                 exo_cfg->flags |= EXOSPHERE_FLAG_IS_DEBUGMODE_PRIV;
             } else {
                 exo_cfg->flags &= ~(EXOSPHERE_FLAG_IS_DEBUGMODE_PRIV);
             }
-        } 
+        } else if (strcmp(name, EXOSPHERE_DEBUGMODE_USER_KEY) == 0) {
-        if (strcmp(name, EXOSPHERE_DEBUGMODE_USER_KEY) == 0) {
             sscanf(value, "%d", &tmp);
             if (tmp) {
                 exo_cfg->flags |= EXOSPHERE_FLAG_IS_DEBUGMODE_USER;
             } else {
                 exo_cfg->flags &= ~(EXOSPHERE_FLAG_IS_DEBUGMODE_USER);
             }
+        } else if (strcmp(name, EXOSPHERE_DISABLE_USERMODE_EXCEPTION_HANDLERS_KEY) == 0) {
+            sscanf(value, "%d", &tmp);
+            if (tmp) {
+                exo_cfg->flags |= EXOSPHERE_FLAG_DISABLE_USERMODE_EXCEPTION_HANDLERS;
+            } else {
+                exo_cfg->flags &= ~(EXOSPHERE_FLAG_DISABLE_USERMODE_EXCEPTION_HANDLERS);
+            }
         } else {
             return 0;
         }