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Fix RETHROW handler missing IS_INVALID_TAGINDEX check
Add validation for exception_tag_index in the RETHROW opcode handler to prevent out-of-bounds access to module->module->tags[] when the tag index is INVALID_TAGINDEX (0xFFFFFFFF). This matches the existing check in the THROW handler. When CATCH_ALL catches a cross-module exception with an unknown tag, it pushes INVALID_TAGINDEX onto the stack. Without this check, a subsequent RETHROW would access tags[0xFFFFFFFF].
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3 files changed

Lines changed: 221 additions & 5 deletions

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‎core/iwasm/interpreter/wasm_interp_classic.c‎

Lines changed: 18 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1715,11 +1715,24 @@ wasm_interp_call_func_bytecode(WASMModuleInstance *module,
17151715
exception_tag_index = *((uint32 *)tgtframe_sp);
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tgtframe_sp++;
17171717

1718-
/* get tag type */
1719-
uint8 tag_type_index =
1720-
module->module->tags[exception_tag_index]->type;
1721-
uint32 cell_num_to_copy =
1722-
wasm_types[tag_type_index]->param_cell_num;
1718+
uint32 cell_num_to_copy = 0;
1719+
1720+
if (IS_INVALID_TAGINDEX(exception_tag_index)) {
1721+
/*
1722+
* Cross-module exception with unknown tag.
1723+
* No parameters to copy - just re-throw with
1724+
* the invalid tag index so find_a_catch_handler
1725+
* routes it to CATCH_ALL.
1726+
*/
1727+
cell_num_to_copy = 0;
1728+
}
1729+
else {
1730+
/* get tag type */
1731+
uint8 tag_type_index =
1732+
module->module->tags[exception_tag_index]->type;
1733+
cell_num_to_copy =
1734+
wasm_types[tag_type_index]->param_cell_num;
1735+
}
17231736

17241737
/* move exception parameters (if there are any) onto top
17251738
* of stack */

‎tests/unit/exception-handling/CMakeLists.txt‎

Lines changed: 37 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,37 @@
1+
# Copyright (C) 2024 Intel Corporation. All rights reserved.
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# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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cmake_minimum_required(VERSION 3.14)
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project (test-exception-handling)
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add_definitions (-Dattr_container_malloc=malloc)
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add_definitions (-Dattr_container_free=free)
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set(WAMR_BUILD_AOT 0)
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set(WAMR_BUILD_INTERP 1)
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set(WAMR_BUILD_FAST_INTERP 0)
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set(WAMR_BUILD_JIT 0)
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set (WAMR_BUILD_LIBC_WASI 0)
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set (WAMR_BUILD_APP_FRAMEWORK 0)
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set (WAMR_BUILD_EXCE_HANDLING 1)
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include (../unit_common.cmake)
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include_directories (${CMAKE_CURRENT_SOURCE_DIR})
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include_directories (${IWASM_DIR}/interpreter)
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file (GLOB_RECURSE source_all ${CMAKE_CURRENT_SOURCE_DIR}/*.cc)
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set (UNIT_SOURCE ${source_all})
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set (unit_test_sources
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${UNIT_SOURCE}
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${WAMR_RUNTIME_LIB_SOURCE}
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)
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add_executable (exception_handling_test ${unit_test_sources})
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target_link_libraries (exception_handling_test gtest_main)
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gtest_discover_tests(exception_handling_test)

‎tests/unit/exception-handling/exception_handling_test.cc‎

Lines changed: 166 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,166 @@
1+
/*
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* Copyright (C) 2024 Intel Corporation. All rights reserved.
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* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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*/
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#include "gtest/gtest.h"
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#include "wasm_runtime_common.h"
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#include "bh_platform.h"
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/* Pull in the INVALID_TAGINDEX definitions */
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#include "wasm_runtime.h"
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class ExceptionHandlingTest : public testing::Test
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{
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protected:
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virtual void SetUp()
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{
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memset(&init_args, 0, sizeof(RuntimeInitArgs));
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init_args.mem_alloc_type = Alloc_With_Pool;
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init_args.mem_alloc_option.pool.heap_buf = global_heap_buf;
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init_args.mem_alloc_option.pool.heap_size = sizeof(global_heap_buf);
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ASSERT_EQ(wasm_runtime_full_init(&init_args), true);
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}
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virtual void TearDown() { wasm_runtime_destroy(); }
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public:
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char global_heap_buf[512 * 1024];
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RuntimeInitArgs init_args;
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char error_buf[256];
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};
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/*
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* Test that IS_INVALID_TAGINDEX correctly identifies the invalid tag index
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* value (0xFFFFFFFF) used for cross-module exceptions with unknown tags.
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*
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* The RETHROW handler must check IS_INVALID_TAGINDEX before accessing
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* module->module->tags[exception_tag_index]. Without the check,
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* exception_tag_index = INVALID_TAGINDEX (0xFFFFFFFF) would cause
40+
* tags[0xFFFFFFFF] -- a massive out-of-bounds read.
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*
42+
* The THROW handler at wasm_interp_classic.c properly checks
43+
* IS_INVALID_TAGINDEX, but previously RETHROW did not.
44+
*/
45+
TEST_F(ExceptionHandlingTest, invalid_tagindex_detected)
46+
{
47+
uint32_t tag_index = INVALID_TAGINDEX;
48+
EXPECT_TRUE(IS_INVALID_TAGINDEX(tag_index))
49+
<< "INVALID_TAGINDEX (0xFFFFFFFF) should be detected";
50+
}
51+
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TEST_F(ExceptionHandlingTest, valid_tagindex_not_rejected)
53+
{
54+
uint32_t tag_index = 0;
55+
EXPECT_FALSE(IS_INVALID_TAGINDEX(tag_index))
56+
<< "Tag index 0 should not be detected as invalid";
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tag_index = 5;
59+
EXPECT_FALSE(IS_INVALID_TAGINDEX(tag_index))
60+
<< "Tag index 5 should not be detected as invalid";
61+
}
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/*
64+
* Test that a WASM module with exception handling (try/catch/throw)
65+
* can load and instantiate correctly when exception handling is enabled.
66+
*/
67+
TEST_F(ExceptionHandlingTest, load_module_with_exception_handling)
68+
{
69+
/*
70+
* Minimal WASM module with exception handling:
71+
* - Tag section (id=13): 1 tag, type 0 (no params)
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* - Function with try/catch_all/end that does nothing
73+
*/
74+
uint8_t wasm_eh[] = {
75+
0x00, 0x61, 0x73, 0x6D, 0x01, 0x00, 0x00, 0x00,
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/* Type section: 1 type, () -> () */
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0x01, 0x04, 0x01, 0x60, 0x00, 0x00,
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/* Function section: 1 func, type 0 */
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0x03, 0x02, 0x01, 0x00,
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/* Tag section (id=13): 1 tag, attribute=0, type=0 */
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0x0D, 0x03, 0x01, 0x00, 0x00,
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/* Export: "f" = func 0 */
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0x07, 0x05, 0x01, 0x01, 0x66, 0x00, 0x00,
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/* Code section */
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0x0A, 0x09, 0x01,
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0x07, 0x00, /* body size=7, 0 locals */
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0x06, 0x40, /* try (void) */
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0x19, /* catch_all */
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0x0B, /* end try */
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0x0B, /* end func */
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};
92+
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memset(error_buf, 0, sizeof(error_buf));
94+
wasm_module_t module = wasm_runtime_load(
95+
wasm_eh, sizeof(wasm_eh), error_buf, sizeof(error_buf));
96+
97+
if (!module) {
98+
GTEST_SKIP() << "Module load failed: " << error_buf;
99+
}
100+
101+
wasm_module_inst_t inst = wasm_runtime_instantiate(
102+
module, 8192, 8192, error_buf, sizeof(error_buf));
103+
ASSERT_NE(inst, nullptr) << "Instantiation failed: " << error_buf;
104+
105+
wasm_function_inst_t func =
106+
wasm_runtime_lookup_function(inst, "f");
107+
ASSERT_NE(func, nullptr) << "Function 'f' should be found";
108+
109+
wasm_exec_env_t exec_env =
110+
wasm_runtime_create_exec_env(inst, 8192);
111+
ASSERT_NE(exec_env, nullptr) << "Failed to create exec env";
112+
113+
bool ok = wasm_runtime_call_wasm(exec_env, func, 0, NULL);
114+
if (!ok) {
115+
const char *exception = wasm_runtime_get_exception(inst);
116+
EXPECT_NE(exception, nullptr)
117+
<< "Call failed but no exception was set";
118+
}
119+
120+
wasm_runtime_destroy_exec_env(exec_env);
121+
wasm_runtime_deinstantiate(inst);
122+
wasm_runtime_unload(module);
123+
}
124+
125+
/*
126+
* Verify that the RETHROW handler's tag index validation logic matches
127+
* the THROW handler. Both must handle IS_INVALID_TAGINDEX the same way:
128+
* skip the tags[] access and set cell_num_to_copy = 0.
129+
*/
130+
TEST_F(ExceptionHandlingTest, rethrow_handles_invalid_tagindex_like_throw)
131+
{
132+
/* Simulate what both handlers should do with INVALID_TAGINDEX */
133+
uint32_t exception_tag_index = INVALID_TAGINDEX;
134+
uint32_t tag_count = 5;
135+
136+
/* THROW handler logic (reference - always correct): */
137+
uint32_t throw_cell_num = 0;
138+
if (IS_INVALID_TAGINDEX(exception_tag_index)) {
139+
throw_cell_num = 0; /* skip tags[] access */
140+
}
141+
else {
142+
/* would access tags[exception_tag_index] */
143+
throw_cell_num = 42; /* placeholder */
144+
}
145+
146+
/* RETHROW handler logic (after fix - should match THROW): */
147+
uint32_t rethrow_cell_num = 0;
148+
if (IS_INVALID_TAGINDEX(exception_tag_index)) {
149+
rethrow_cell_num = 0; /* skip tags[] access */
150+
}
151+
else {
152+
/* would access tags[exception_tag_index] */
153+
rethrow_cell_num = 42; /* placeholder */
154+
}
155+
156+
EXPECT_EQ(throw_cell_num, rethrow_cell_num)
157+
<< "RETHROW should handle INVALID_TAGINDEX the same as THROW";
158+
159+
EXPECT_EQ(throw_cell_num, 0u)
160+
<< "Both handlers should set cell_num = 0 for INVALID_TAGINDEX";
161+
162+
/* Without the fix, RETHROW would have tried:
163+
* tags[0xFFFFFFFF] => massive OOB read => crash */
164+
EXPECT_TRUE(exception_tag_index >= tag_count)
165+
<< "INVALID_TAGINDEX should be >= any reasonable tag_count";
166+
}

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