[wasm] Fix out-of-bound behavior for bulk ops

The bulk memory operations should not bounds check ahead of time, but
instead should write as many bytes as possible until the first
out-of-bounds access.

Bug: v8:8890
Change-Id: Ia8179fe268fc65816c34a8f3461ed0a0d35600aa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1497520
Commit-Queue: Ben Smith <binji@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60040}

src/compiler/wasm-compiler.cc

@@ -3405,37 +3405,32 @@ Node* WasmGraphBuilder::BoundsCheckMem(uint8_t access_size, Node* index,
   return index;
 }
 
-// Check that the range [start, start + size) is in the range [0, max).
-void WasmGraphBuilder::BoundsCheckRange(Node* start, Node* size, Node* max,
-                                        wasm::WasmCodePosition position) {
-  // The accessed memory is [start, end), where {end} is {start + size}. We
-  // want to check that {start + size <= max}, making sure that {start + size}
-  // doesn't overflow. This can be expressed as {start <= max - size} as long
-  // as {max - size} isn't negative, which is true if {size <= max}.
+Node* WasmGraphBuilder::BoundsCheckRange(Node* start, Node** size, Node* max,
+                                         wasm::WasmCodePosition position) {
   auto m = mcgraph()->machine();
-  Node* cond = graph()->NewNode(m->Uint32LessThanOrEqual(), size, max);
-  TrapIfFalse(wasm::kTrapMemOutOfBounds, cond, position);
-
-  // This produces a positive number, since {size <= max}.
-  Node* effective_size = graph()->NewNode(m->Int32Sub(), max, size);
-
-  // Introduce the actual bounds check.
-  Node* check =
-      graph()->NewNode(m->Uint32LessThanOrEqual(), start, effective_size);
-  TrapIfFalse(wasm::kTrapMemOutOfBounds, check, position);
-
-  // TODO(binji): Does this need addtional untrusted_code_mitigations_ mask
-  // like BoundsCheckMem above?
+  // The region we are trying to access is [start, start+size). If
+  // {start} > {max}, none of this region is valid, so we trap. Otherwise,
+  // there may be a subset of the region that is valid. {max - start} is the
+  // maximum valid size, so if {max - start < size}, then the region is
+  // partially out-of-bounds.
+  TrapIfTrue(wasm::kTrapMemOutOfBounds,
+             graph()->NewNode(m->Uint32LessThan(), max, start), position);
+  Node* sub = graph()->NewNode(m->Int32Sub(), max, start);
+  Node* fail = graph()->NewNode(m->Uint32LessThan(), sub, *size);
+  Diamond d(graph(), mcgraph()->common(), fail, BranchHint::kFalse);
+  d.Chain(Control());
+  *size = d.Phi(MachineRepresentation::kWord32, sub, *size);
+  return fail;
 }
 
-Node* WasmGraphBuilder::BoundsCheckMemRange(Node* start, Node* size,
+Node* WasmGraphBuilder::BoundsCheckMemRange(Node** start, Node** size,
                                             wasm::WasmCodePosition position) {
-  // TODO(binji): Support trap handler.
-  if (!FLAG_wasm_no_bounds_checks) {
-    BoundsCheckRange(start, size, instance_cache_->mem_size, position);
-  }
-  return graph()->NewNode(mcgraph()->machine()->IntAdd(), MemBuffer(0),
-                          Uint32ToUintptr(start));
+  // TODO(binji): Support trap handler and no bounds check mode.
+  Node* fail =
+      BoundsCheckRange(*start, size, instance_cache_->mem_size, position);
+  *start = graph()->NewNode(mcgraph()->machine()->IntAdd(), MemBuffer(0),
+                            Uint32ToUintptr(*start));
+  return fail;
 }
 
 const Operator* WasmGraphBuilder::GetSafeLoadOperator(int offset,
@@ -4377,10 +4372,11 @@ Node* WasmGraphBuilder::MemoryInit(uint32_t data_segment_index, Node* dst,
                                    Node* src, Node* size,
                                    wasm::WasmCodePosition position) {
   CheckDataSegmentIsPassiveAndNotDropped(data_segment_index, position);
-  dst = BoundsCheckMemRange(dst, size, position);
-  MachineOperatorBuilder* m = mcgraph()->machine();
+  Node* dst_fail = BoundsCheckMemRange(&dst, &size, position);
+  auto m = mcgraph()->machine();
 
   Node* seg_index = Uint32Constant(data_segment_index);
+  Node* src_fail;
 
   {
     // Load segment size from WasmInstanceObject::data_segment_sizes.
@@ -4394,7 +4390,7 @@ Node* WasmGraphBuilder::MemoryInit(uint32_t data_segment_index, Node* dst,
                                                 Effect(), Control()));
 
     // Bounds check the src index against the segment size.
-    BoundsCheckRange(src, size, seg_size, position);
+    src_fail = BoundsCheckRange(src, &size, seg_size, position);
   }
 
   {
@@ -4418,7 +4414,10 @@ Node* WasmGraphBuilder::MemoryInit(uint32_t data_segment_index, Node* dst,
   MachineType sig_types[] = {MachineType::Pointer(), MachineType::Pointer(),
                              MachineType::Uint32()};
   MachineSignature sig(0, 3, sig_types);
-  return BuildCCall(&sig, function, dst, src, size);
+  BuildCCall(&sig, function, dst, src, size);
+  return TrapIfTrue(wasm::kTrapMemOutOfBounds,
+                    graph()->NewNode(m->Word32Or(), dst_fail, src_fail),
+                    position);
 }
 
 Node* WasmGraphBuilder::DataDrop(uint32_t data_segment_index,
@@ -4435,25 +4434,51 @@ Node* WasmGraphBuilder::DataDrop(uint32_t data_segment_index,
 
 Node* WasmGraphBuilder::MemoryCopy(Node* dst, Node* src, Node* size,
                                    wasm::WasmCodePosition position) {
-  dst = BoundsCheckMemRange(dst, size, position);
-  src = BoundsCheckMemRange(src, size, position);
+  auto m = mcgraph()->machine();
+  // The data must be copied backward if the regions overlap and src < dst. The
+  // regions overlap if {src + size > dst && dst + size > src}. Since we already
+  // test that {src < dst}, we know that {dst + size > src}, so this simplifies
+  // to just {src + size > dst}. That sum can overflow, but if we subtract
+  // {size} from both sides of the inequality we get the equivalent test
+  // {size > dst - src}.
+  Node* copy_backward = graph()->NewNode(
+      m->Word32And(), graph()->NewNode(m->Uint32LessThan(), src, dst),
+      graph()->NewNode(m->Uint32LessThan(),
+                       graph()->NewNode(m->Int32Sub(), dst, src), size));
+
+  Node* dst_fail = BoundsCheckMemRange(&dst, &size, position);
+
+  // Trap without copying any bytes if we are copying backward and the copy is
+  // partially out-of-bounds. We only need to check that the dst region is
+  // out-of-bounds, because we know that {src < dst}, so the src region is
+  // always out of bounds if the dst region is.
+  TrapIfTrue(wasm::kTrapMemOutOfBounds,
+             graph()->NewNode(m->Word32And(), dst_fail, copy_backward),
+             position);
+
+  Node* src_fail = BoundsCheckMemRange(&src, &size, position);
+
   Node* function = graph()->NewNode(mcgraph()->common()->ExternalConstant(
       ExternalReference::wasm_memory_copy()));
   MachineType sig_types[] = {MachineType::Pointer(), MachineType::Pointer(),
                              MachineType::Uint32()};
   MachineSignature sig(0, 3, sig_types);
-  return BuildCCall(&sig, function, dst, src, size);
+  BuildCCall(&sig, function, dst, src, size);
+  return TrapIfTrue(wasm::kTrapMemOutOfBounds,
+                    graph()->NewNode(m->Word32Or(), dst_fail, src_fail),
+                    position);
 }
 
 Node* WasmGraphBuilder::MemoryFill(Node* dst, Node* value, Node* size,
                                    wasm::WasmCodePosition position) {
-  dst = BoundsCheckMemRange(dst, size, position);
+  Node* fail = BoundsCheckMemRange(&dst, &size, position);
   Node* function = graph()->NewNode(mcgraph()->common()->ExternalConstant(
       ExternalReference::wasm_memory_fill()));
   MachineType sig_types[] = {MachineType::Pointer(), MachineType::Uint32(),
                              MachineType::Uint32()};
   MachineSignature sig(0, 3, sig_types);
-  return BuildCCall(&sig, function, dst, value, size);
+  BuildCCall(&sig, function, dst, value, size);
+  return TrapIfTrue(wasm::kTrapMemOutOfBounds, fail, position);
 }
 
 Node* WasmGraphBuilder::CheckElemSegmentIsPassiveAndNotDropped(

src/compiler/wasm-compiler.h

@@ -441,11 +441,16 @@ class WasmGraphBuilder {
   Node* BoundsCheckMem(uint8_t access_size, Node* index, uint32_t offset,
                        wasm::WasmCodePosition, EnforceBoundsCheck);
   // Check that the range [start, start + size) is in the range [0, max).
-  void BoundsCheckRange(Node* start, Node* size, Node* max,
-                        wasm::WasmCodePosition);
-  // BoundsCheckMemRange receives a uint32 {start} and {size} and returns
-  // a pointer into memory at that index, if it is in bounds.
-  Node* BoundsCheckMemRange(Node* start, Node* size, wasm::WasmCodePosition);
+  // Also updates *size with the valid range. Returns true if the range is
+  // partially out-of-bounds, traps if it is completely out-of-bounds.
+  Node* BoundsCheckRange(Node* start, Node** size, Node* max,
+                         wasm::WasmCodePosition);
+  // BoundsCheckMemRange receives a uint32 {start} and {size}, and checks if it
+  // is in bounds. Also updates *size with the valid range, and converts *start
+  // to a pointer into memory at that index. Returns true if the range is
+  // partially out-of-bounds, traps if it is completely out-of-bounds.
+  Node* BoundsCheckMemRange(Node** start, Node** size, wasm::WasmCodePosition);
+
   Node* CheckBoundsAndAlignment(uint8_t access_size, Node* index,
                                 uint32_t offset, wasm::WasmCodePosition);
 

src/utils.h

@@ -74,6 +74,21 @@ inline constexpr bool IsInBounds(size_t index, size_t length, size_t max) {
   return length <= max && index <= (max - length);
 }
 
+// Checks if [index, index+length) is in range [0, max). If not, {length} is
+// clamped to its valid range. Note that this check works even if
+// {index+length} would wrap around.
+template <typename T>
+inline bool ClampToBounds(T index, T* length, T max) {
+  if (index > max) {
+    *length = 0;
+    return false;
+  }
+  T avail = max - index;
+  bool oob = *length > avail;
+  if (oob) *length = avail;
+  return !oob;
+}
+
 // X must be a power of 2.  Returns the number of trailing zeros.
 template <typename T,
           typename = typename std::enable_if<std::is_integral<T>::value>::type>

src/wasm/module-instantiate.cc

@@ -1481,11 +1481,12 @@ bool LoadElemSegmentImpl(Isolate* isolate, Handle<WasmInstanceObject> instance,
   // TODO(wasm): Move this functionality into wasm-objects, since it is used
   // for both instantiation and in the implementation of the table.init
   // instruction.
-  if (!IsInBounds(dst, count, table_instance.table_size)) return false;
-  if (!IsInBounds(src, count, elem_segment.entries.size())) return false;
+  bool ok = ClampToBounds<size_t>(dst, &count, table_instance.table_size);
+  // Use & instead of && so the clamp is not short-circuited.
+  ok &= ClampToBounds<size_t>(src, &count, elem_segment.entries.size());
 
   const WasmModule* module = instance->module();
-  for (uint32_t i = 0; i < count; ++i) {
+  for (size_t i = 0; i < count; ++i) {
     uint32_t func_index = elem_segment.entries[src + i];
     int entry_index = static_cast<int>(dst + i);
 
@@ -1547,7 +1548,7 @@ bool LoadElemSegmentImpl(Isolate* isolate, Handle<WasmInstanceObject> instance,
           instance, func_index);
     }
   }
-  return true;
+  return ok;
 }
 
 void InstanceBuilder::LoadTableSegments(Handle<WasmInstanceObject> instance) {

src/wasm/wasm-objects.cc

@@ -1442,9 +1442,9 @@ Address WasmInstanceObject::GetCallTarget(uint32_t func_index) {
 
 namespace {
 void CopyTableEntriesImpl(Handle<WasmInstanceObject> instance, uint32_t dst,
-                          uint32_t src, uint32_t count) {
+                          uint32_t src, uint32_t count, bool copy_backward) {
   DCHECK(IsInBounds(dst, count, instance->indirect_function_table_size()));
-  if (src < dst) {
+  if (copy_backward) {
     for (uint32_t i = count; i > 0; i--) {
       auto to_entry = IndirectFunctionTableEntry(instance, dst + i - 1);
       auto from_entry = IndirectFunctionTableEntry(instance, src + i - 1);
@@ -1471,14 +1471,21 @@ bool WasmInstanceObject::CopyTableEntries(Isolate* isolate,
   CHECK_EQ(0, table_src_index);
   CHECK_EQ(0, table_dst_index);
   auto max = instance->indirect_function_table_size();
-  if (!IsInBounds(dst, count, max)) return false;
-  if (!IsInBounds(src, count, max)) return false;
-  if (dst == src) return true;  // no-op
+  bool copy_backward = src < dst && dst - src < count;
+  bool ok = ClampToBounds(dst, &count, max);
+  // Use & instead of && so the clamp is not short-circuited.
+  ok &= ClampToBounds(src, &count, max);
+
+  // If performing a partial copy when copying backward, then the first access
+  // will be out-of-bounds, so no entries should be copied.
+  if (copy_backward && !ok) return ok;
+
+  if (dst == src || count == 0) return ok;  // no-op
 
   if (!instance->has_table_object()) {
     // No table object, only need to update this instance.
-    CopyTableEntriesImpl(instance, dst, src, count);
-    return true;
+    CopyTableEntriesImpl(instance, dst, src, count, copy_backward);
+    return ok;
   }
 
   Handle<WasmTableObject> table =
@@ -1491,12 +1498,12 @@ bool WasmInstanceObject::CopyTableEntries(Isolate* isolate,
         WasmInstanceObject::cast(
             dispatch_tables->get(i + kDispatchTableInstanceOffset)),
         isolate);
-    CopyTableEntriesImpl(target_instance, dst, src, count);
+    CopyTableEntriesImpl(target_instance, dst, src, count, copy_backward);
   }
 
   // Copy the function entries.
   Handle<FixedArray> functions(table->elements(), isolate);
-  if (src < dst) {
+  if (copy_backward) {
     for (uint32_t i = count; i > 0; i--) {
       functions->set(dst + i - 1, functions->get(src + i - 1));
     }
@@ -1505,7 +1512,7 @@ bool WasmInstanceObject::CopyTableEntries(Isolate* isolate,
       functions->set(dst + i, functions->get(src + i));
     }
   }
-  return true;
+  return ok;
 }
 
 // static

test/mjsunit/wasm/bulk-memory.js

@@ -71,8 +71,35 @@ function getMemoryInit(mem, segment_data) {
   memoryInit(0, 5, 5);
   assertBufferContents(u8a, [5, 6, 7, 8, 9, 0, 0, 0, 0, 0,
                              0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
+
+  // Copy 0 bytes does nothing.
+  memoryInit(10, 1, 0);
+  assertBufferContents(u8a, [5, 6, 7, 8, 9, 0, 0, 0, 0, 0,
+                             0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
+
+  // Copy 0 at end of memory region or data segment is OK.
+  memoryInit(kPageSize, 0, 0);
+  memoryInit(0, 10, 0);
 })();
 
+(function TestMemoryInitOutOfBoundsData() {
+  const mem = new WebAssembly.Memory({initial: 1});
+  const memoryInit = getMemoryInit(mem, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
+
+  const u8a = new Uint8Array(mem.buffer);
+  const last5Bytes = new Uint8Array(mem.buffer, kPageSize - 5);
+
+  // Write all values up to the out-of-bounds write.
+  assertTraps(kTrapMemOutOfBounds, () => memoryInit(kPageSize - 5, 0, 6));
+  assertBufferContents(last5Bytes, [0, 1, 2, 3, 4]);
+
+  // Write all values up to the out-of-bounds read.
+  u8a.fill(0);
+  assertTraps(kTrapMemOutOfBounds, () => memoryInit(0, 5, 6));
+  assertBufferContents(u8a, [5, 6, 7, 8, 9]);
+})();
+
+
 (function TestMemoryInitOutOfBounds() {
   const mem = new WebAssembly.Memory({initial: 1});
   // Create a data segment that has a length of kPageSize.
@@ -91,6 +118,10 @@ function getMemoryInit(mem, segment_data) {
   assertTraps(kTrapMemOutOfBounds, () => memoryInit(1000, 0, kPageSize));
   assertTraps(kTrapMemOutOfBounds, () => memoryInit(kPageSize, 0, 1));
 
+  // Copy 0 out-of-bounds fails.
+  assertTraps(kTrapMemOutOfBounds, () => memoryInit(kPageSize + 1, 0, 0));
+  assertTraps(kTrapMemOutOfBounds, () => memoryInit(0, kPageSize + 1, 0));
+
   // Make sure bounds aren't checked with 32-bit wrapping.
   assertTraps(kTrapMemOutOfBounds, () => memoryInit(1, 1, -1));
 
@@ -206,6 +237,10 @@ function getMemoryCopy(mem) {
   memoryCopy(10, 1, 0);
   assertBufferContents(u8a, [0, 11, 22, 33, 44, 55, 66, 77, 0, 0,
                              11, 22, 33, 44, 55, 66, 77]);
+
+  // Copy 0 at end of memory region is OK.
+  memoryCopy(kPageSize, 0, 0);
+  memoryCopy(0, kPageSize, 0);
 })();
 
 (function TestMemoryCopyOverlapping() {
@@ -226,6 +261,36 @@ function getMemoryCopy(mem) {
   assertBufferContents(u8a, [10, 20, 30, 20, 30]);
 })();
 
+(function TestMemoryCopyOutOfBoundsData() {
+  const mem = new WebAssembly.Memory({initial: 1});
+  const memoryCopy = getMemoryCopy(mem);
+
+  const u8a = new Uint8Array(mem.buffer);
+  const first5Bytes = new Uint8Array(mem.buffer, 0, 5);
+  const last5Bytes = new Uint8Array(mem.buffer, kPageSize - 5);
+  u8a.set([11, 22, 33, 44, 55, 66, 77, 88]);
+
+  // Write all values up to the out-of-bounds access.
+  assertTraps(kTrapMemOutOfBounds, () => memoryCopy(kPageSize - 5, 0, 6));
+  assertBufferContents(last5Bytes, [11, 22, 33, 44, 55]);
+
+  // Copy overlapping with destination < source. Copy will happen forwards, up
+  // to the out-of-bounds access.
+  u8a.fill(0);
+  last5Bytes.set([11, 22, 33, 44, 55]);
+  assertTraps(
+      kTrapMemOutOfBounds, () => memoryCopy(0, kPageSize - 5, kPageSize));
+  assertBufferContents(first5Bytes, [11, 22, 33, 44, 55]);
+
+  // Copy overlapping with source < destination. Copy would happen backwards,
+  // but the first byte to copy is out-of-bounds, so no data should be written.
+  u8a.fill(0);
+  first5Bytes.set([11, 22, 33, 44, 55]);
+  assertTraps(
+      kTrapMemOutOfBounds, () => memoryCopy(kPageSize - 5, 0, kPageSize));
+  assertBufferContents(last5Bytes, [0, 0, 0, 0, 0]);
+})();
+
 (function TestMemoryCopyOutOfBounds() {
   const mem = new WebAssembly.Memory({initial: 1});
   const memoryCopy = getMemoryCopy(mem);
@@ -242,6 +307,10 @@ function getMemoryCopy(mem) {
   assertTraps(kTrapMemOutOfBounds, () => memoryCopy(1000, 0, kPageSize));
   assertTraps(kTrapMemOutOfBounds, () => memoryCopy(kPageSize, 0, 1));
 
+  // Copy 0 out-of-bounds fails.
+  assertTraps(kTrapMemOutOfBounds, () => memoryCopy(kPageSize + 1, 0, 0));
+  assertTraps(kTrapMemOutOfBounds, () => memoryCopy(0, kPageSize + 1, 0));
+
   // Make sure bounds aren't checked with 32-bit wrapping.
   assertTraps(kTrapMemOutOfBounds, () => memoryCopy(1, 1, -1));
 
@@ -282,6 +351,9 @@ function getMemoryFill(mem) {
   // Fill 0 bytes does nothing.
   memoryFill(4, 66, 0);
   assertBufferContents(u8a, [0, 33, 33, 33, 66, 66, 66, 66]);
+
+  // Fill 0 at end of memory region is OK.
+  memoryFill(kPageSize, 66, 0);
 })();
 
 (function TestMemoryFillValueWrapsToByte() {
@@ -295,6 +367,17 @@ function getMemoryFill(mem) {
   assertBufferContents(u8a, [expected, expected, expected]);
 })();
 
+(function TestMemoryFillOutOfBoundsData() {
+  const mem = new WebAssembly.Memory({initial: 1});
+  const memoryFill = getMemoryFill(mem);
+  const v = 123;
+
+  // Write all values up to the out-of-bound access.
+  assertTraps(kTrapMemOutOfBounds, () => memoryFill(kPageSize - 5, v, 999));
+  const u8a = new Uint8Array(mem.buffer, kPageSize - 6);
+  assertBufferContents(u8a, [0, 123, 123, 123, 123, 123]);
+})();
+
 (function TestMemoryFillOutOfBounds() {
   const mem = new WebAssembly.Memory({initial: 1});
   const memoryFill = getMemoryFill(mem);
@@ -307,6 +390,9 @@ function getMemoryFill(mem) {
   assertTraps(kTrapMemOutOfBounds, () => memoryFill(1000, v, kPageSize));
   assertTraps(kTrapMemOutOfBounds, () => memoryFill(kPageSize, v, 1));
 
+  // Fill 0 out-of-bounds fails.
+  assertTraps(kTrapMemOutOfBounds, () => memoryFill(kPageSize + 1, v, 0));
+
   // Make sure bounds aren't checked with 32-bit wrapping.
   assertTraps(kTrapMemOutOfBounds, () => memoryFill(1, v, -1));
 

test/mjsunit/wasm/table-copy.js

@@ -24,7 +24,7 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
 
   let instance = builder.instantiate();
   let copy = instance.exports.copy;
-  for (let i = 0; i < kTableSize; i++) {
+  for (let i = 0; i <= kTableSize; i++) {
     copy(0, 0, i); // nop
     copy(0, i, kTableSize - i);
     copy(i, 0, kTableSize - i);
@@ -147,6 +147,54 @@ function assertCall(call, ...elems) {
   assertCall(call, 1, 2, 2, 1, 2);
 })();
 
+(function TestTableCopyOobWrites() {
+  print(arguments.callee.name);
+
+  let builder = new WasmModuleBuilder();
+  let sig_v_iii = builder.addType(kSig_v_iii);
+  let kTableSize = 5;
+
+  builder.setTableBounds(kTableSize, kTableSize);
+
+  {
+    let o = addFunctions(builder, kTableSize);
+    builder.addElementSegment(0, false,
+       [o.f0.index, o.f1.index, o.f2.index]);
+  }
+
+  builder.addFunction("copy", sig_v_iii)
+    .addBody([
+      kExprGetLocal, 0,
+      kExprGetLocal, 1,
+      kExprGetLocal, 2,
+      kNumericPrefix, kExprTableCopy, kTableZero, kTableZero])
+    .exportAs("copy");
+
+  builder.addExportOfKind("table", kExternalTable, 0);
+
+  let instance = builder.instantiate();
+  let table = instance.exports.table;
+  let f0 = table.get(0), f1 = table.get(1), f2 = table.get(2);
+  let copy = instance.exports.copy;
+
+  // Non-overlapping, src < dst.
+  assertThrows(() => copy(3, 0, 3));
+  assertTable(table, f0, f1, f2, f0, f1);
+
+  // Non-overlapping, dst < src.
+  assertThrows(() => copy(0, 4, 2));
+  assertTable(table, f1, f1, f2, f0, f1);
+
+  // Overlapping, src < dst. This is required to copy backward, but the first
+  // access will be out-of-bounds, so nothing changes.
+  assertThrows(() => copy(3, 0, 99));
+  assertTable(table, f1, f1, f2, f0, f1);
+
+  // Overlapping, dst < src.
+  assertThrows(() => copy(0, 1, 99));
+  assertTable(table, f1, f2, f0, f1, f1);
+})();
+
 (function TestTableCopyOob1() {
   print(arguments.callee.name);
 

test/mjsunit/wasm/table-init.js

@@ -12,12 +12,12 @@ function addFunction(builder, k) {
   return m;
 }
 
-function addFunctions(builder, count, exportf = false) {
+function addFunctions(builder, count) {
   let o = {};
   for (var i = 0; i < count; i++) {
     let name = `f${i}`;
     o[name] = addFunction(builder, i);
-    if (exportf) o[name].exportAs(name);
+    o[name].exportAs(name);
   }
   return o;
 }
@@ -36,7 +36,7 @@ function assertTable(obj, ...elems) {
 
   builder.setTableBounds(kTableSize, kTableSize);
   {
-    let o = addFunctions(builder, kTableSize, true);
+    let o = addFunctions(builder, kTableSize);
     builder.addPassiveElementSegment(
        [o.f0.index, o.f1.index, o.f2.index, o.f3.index, o.f4.index, null]);
   }
@@ -56,6 +56,11 @@ function assertTable(obj, ...elems) {
 
   assertTable(x.table, null, null, null, null, null);
 
+  // 0 count is ok in bounds, and at end of regions.
+  x.init0(0, 0, 0);
+  x.init0(kTableSize, 0, 0);
+  x.init0(0, kTableSize, 0);
+
   // test actual writes.
   x.init0(0, 0, 1);
   assertTable(x.table, x.f0, null, null, null, null);
@@ -105,6 +110,14 @@ function assertTable(obj, ...elems) {
 
   assertTable(x.table, null, null, null, null, null);
 
+  // Write all values up to the out-of-bounds write.
+  assertThrows(() => x.init0(3, 0, 3));
+  assertTable(x.table, null, null, null, x.f0, x.f1);
+
+  // Write all values up to the out-of-bounds read.
+  assertThrows(() => x.init0(0, 3, 3));
+  assertTable(x.table, x.f3, x.f4, null, x.f0, x.f1);
+
   // 0-count is oob.
   assertThrows(() => x.init0(kTableSize+1, 0, 0));
   assertThrows(() => x.init0(0, kTableSize+1, 0));