Make undefined behavior check optional

Signed-off-by: Alan Jowett <[email protected]>

libfuzzer/libfuzz_harness.cc

@@ -112,8 +112,11 @@ int LLVMFuzzerTestOneInput(const uint8_t* data, std::size_t size)
         return -1;
     }
 
+    ubpf_toggle_undefined_behavior_check(vm.get(), true);
+
     char* error_message = nullptr;
 
+
     if (ubpf_load(vm.get(), program_start, program_length, &error_message) != 0) {
         // The program failed to load, due to a validation error.
         // This is not interesting, as the fuzzer input is invalid.

vm/inc/ubpf.h

@@ -544,6 +544,18 @@ extern "C"
     int
     ubpf_set_instruction_limit(struct ubpf_vm* vm, uint32_t limit, uint32_t* previous_limit);
 
+
+    /**
+     * @brief Enable or disable undefined behavior checks. Undefined behavior includes
+     * reading from uninitialized memory or using uninitialized registers.
+     *
+     * @param[in] vm VM to enable or disable undefined behavior checks on.
+     * @param[in] enable Enable undefined behavior checks if true, disable if false.
+     * @return true if undefined behavior checks were previously enabled.
+     * @return false if undefined behavior checks were previously disabled.
+     */
+    bool
+    ubpf_toggle_undefined_behavior_check(struct ubpf_vm* vm, bool enable);
 #ifdef __cplusplus
 }
 #endif

vm/ubpf_int.h

@@ -74,6 +74,7 @@ struct ubpf_vm
     external_function_validate_t dispatcher_validate;
 
     bool bounds_check_enabled;
+    bool undefined_behavior_check_enabled;
     int (*error_printf)(FILE* stream, const char* format, ...);
     struct ubpf_jit_result (*jit_translate)(struct ubpf_vm* vm, uint8_t* buffer, size_t* size, enum JitMode jit_mode);
     bool (*jit_update_dispatcher)(

vm/ubpf_vm.c

@@ -56,6 +56,14 @@ ubpf_toggle_bounds_check(struct ubpf_vm* vm, bool enable)
     return old;
 }
 
+bool
+ubpf_toggle_undefined_behavior_check(struct ubpf_vm* vm, bool enable)
+{
+    bool old = vm->undefined_behavior_check_enabled;
+    vm->undefined_behavior_check_enabled = enable;
+    return old;
+}
+
 void
 ubpf_set_error_print(struct ubpf_vm* vm, int (*error_printf)(FILE* stream, const char* format, ...))
 {
@@ -105,6 +113,7 @@ ubpf_create(void)
     }
 
     vm->bounds_check_enabled = true;
+    vm->undefined_behavior_check_enabled = false;
     vm->error_printf = fprintf;
 
 #if defined(__x86_64__) || defined(_M_X64)
@@ -385,7 +394,7 @@ static inline void
 ubpf_mark_shadow_stack(
     const struct ubpf_vm* vm, uint8_t* stack, uint64_t stack_length, uint8_t* shadow_stack, void* address, size_t size)
 {
-    if (!vm->bounds_check_enabled) {
+    if (!vm->undefined_behavior_check_enabled) {
         return;
     }
 
@@ -426,7 +435,7 @@ static inline bool
 ubpf_check_shadow_stack(
     const struct ubpf_vm* vm, uint8_t* stack, uint64_t stack_length, uint8_t* shadow_stack, void* address, size_t size)
 {
-    if (!vm->bounds_check_enabled) {
+    if (!vm->undefined_behavior_check_enabled) {
         return true;
     }
 
@@ -469,6 +478,10 @@ ubpf_check_shadow_stack(
 static inline bool
 ubpf_validate_shadow_register(const struct ubpf_vm* vm, uint16_t* shadow_registers, struct ebpf_inst inst)
 {
+    if (!vm->undefined_behavior_check_enabled) {
+        return true;
+    }
+
     bool src_register_required = false;
     bool dst_register_required = false;
     bool dst_register_initialized = false;
@@ -603,7 +616,7 @@ ubpf_exec_ex(
         0,
     };
 
-    if (vm->bounds_check_enabled) {
+    if (vm->undefined_behavior_check_enabled) {
         shadow_stack = calloc(stack_length / 8, 1);
         if (!shadow_stack) {
             return_value = -1;