[wasm][bulk-memory] Check segment bounds lazily

The bulk memory proposal changed behavior of segment initialization
during instantiation. Previously, all segments would be bounds-checked,
after which the segments would be initialized.

The bulk memory proposal removes the up-front check, and always
initializes active segments in order, starting with element segments and
then continuing with data segments. Each active segment is initialized
as-if they were being initialized with the `memory.init` and
`table.init` instructions, so an out-of-bounds initialization may still
modify the memory or table partially.

Bug: v8:8892
Change-Id: I472fca2401e07d60b288f0cc745629a451b31088
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1565033
Commit-Queue: Ben Smith <binji@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60885}

src/wasm/module-instantiate.cc

@@ -11,6 +11,7 @@
 #include "src/tracing/trace-event.h"
 #include "src/utils.h"
 #include "src/wasm/module-compiler.h"
+#include "src/wasm/wasm-external-refs.h"
 #include "src/wasm/wasm-import-wrapper-cache.h"
 #include "src/wasm/wasm-module.h"
 #include "src/wasm/wasm-objects-inl.h"
@@ -445,34 +446,39 @@ MaybeHandle<WasmInstanceObject> InstanceBuilder::Build() {
     }
   }
 
-  //--------------------------------------------------------------------------
+  // The bulk memory proposal changes the MVP behavior here; the segments are
-  // Check that indirect function table segments are within bounds.
+  // written as if `memory.init` and `table.init` are executed directly, and
-  //--------------------------------------------------------------------------
+  // not bounds checked ahead of time.
-  for (const WasmElemSegment& elem_segment : module_->elem_segments) {
+  if (!enabled_.bulk_memory) {
-    if (!elem_segment.active) continue;
+    //--------------------------------------------------------------------------
-    DCHECK_LT(elem_segment.table_index, table_count);
+    // Check that indirect function table segments are within bounds.
-    uint32_t base = EvalUint32InitExpr(instance, elem_segment.offset);
+    //--------------------------------------------------------------------------
-    // Because of imported tables, {table_size} has to come from the table
+    for (const WasmElemSegment& elem_segment : module_->elem_segments) {
-    // object itself.
+      if (!elem_segment.active) continue;
-    auto table_object = handle(WasmTableObject::cast(instance->tables()->get(
+      DCHECK_LT(elem_segment.table_index, table_count);
-                                   elem_segment.table_index)),
+      uint32_t base = EvalUint32InitExpr(instance, elem_segment.offset);
-                               isolate_);
+      // Because of imported tables, {table_size} has to come from the table
-    size_t table_size = table_object->elements()->length();
+      // object itself.
-    if (!IsInBounds(base, elem_segment.entries.size(), table_size)) {
+      auto table_object = handle(WasmTableObject::cast(instance->tables()->get(
-      thrower_->LinkError("table initializer is out of bounds");
+                                     elem_segment.table_index)),
-      return {};
+                                 isolate_);
+      size_t table_size = table_object->elements()->length();
+      if (!IsInBounds(base, elem_segment.entries.size(), table_size)) {
+        thrower_->LinkError("table initializer is out of bounds");
+        return {};
+      }
     }
-  }
 
-  //--------------------------------------------------------------------------
+    //--------------------------------------------------------------------------
-  // Check that memory segments are within bounds.
+    // Check that memory segments are within bounds.
-  //--------------------------------------------------------------------------
+    //--------------------------------------------------------------------------
-  for (const WasmDataSegment& seg : module_->data_segments) {
+    for (const WasmDataSegment& seg : module_->data_segments) {
-    if (!seg.active) continue;
+      if (!seg.active) continue;
-    uint32_t base = EvalUint32InitExpr(instance, seg.dest_addr);
+      uint32_t base = EvalUint32InitExpr(instance, seg.dest_addr);
-    if (!IsInBounds(base, seg.source.length(), instance->memory_size())) {
+      if (!IsInBounds(base, seg.source.length(), instance->memory_size())) {
-      thrower_->LinkError("data segment is out of bounds");
+        thrower_->LinkError("data segment is out of bounds");
-      return {};
+        return {};
+      }
     }
   }
 
@@ -487,6 +493,7 @@ MaybeHandle<WasmInstanceObject> InstanceBuilder::Build() {
   //--------------------------------------------------------------------------
   if (table_count > 0) {
     LoadTableSegments(instance);
+    if (thrower_->error()) return {};
   }
 
   //--------------------------------------------------------------------------
@@ -494,6 +501,7 @@ MaybeHandle<WasmInstanceObject> InstanceBuilder::Build() {
   //--------------------------------------------------------------------------
   if (module_->data_segments.size() > 0) {
     LoadDataSegments(instance);
+    if (thrower_->error()) return {};
   }
 
   //--------------------------------------------------------------------------
@@ -617,16 +625,35 @@ void InstanceBuilder::LoadDataSegments(Handle<WasmInstanceObject> instance) {
   Vector<const uint8_t> wire_bytes =
       module_object_->native_module()->wire_bytes();
   for (const WasmDataSegment& segment : module_->data_segments) {
-    uint32_t source_size = segment.source.length();
+    uint32_t size = segment.source.length();
-    // Segments of size == 0 are just nops.
+
-    if (source_size == 0) continue;
+    if (enabled_.bulk_memory) {
-    // Passive segments are not copied during instantiation.
+      // Passive segments are not copied during instantiation.
-    if (!segment.active) continue;
+      if (!segment.active) continue;
-    uint32_t dest_offset = EvalUint32InitExpr(instance, segment.dest_addr);
+
-    DCHECK(IsInBounds(dest_offset, source_size, instance->memory_size()));
+      uint32_t dest_offset = EvalUint32InitExpr(instance, segment.dest_addr);
-    byte* dest = instance->memory_start() + dest_offset;
+      bool ok = ClampToBounds(dest_offset, &size,
-    const byte* src = wire_bytes.start() + segment.source.offset();
+                              static_cast<uint32_t>(instance->memory_size()));
-    memcpy(dest, src, source_size);
+      Address dest_addr =
+          reinterpret_cast<Address>(instance->memory_start()) + dest_offset;
+      Address src_addr = reinterpret_cast<Address>(wire_bytes.start()) +
+                         segment.source.offset();
+      memory_copy_wrapper(dest_addr, src_addr, size);
+      if (!ok) {
+        thrower_->LinkError("data segment is out of bounds");
+        return;
+      }
+    } else {
+      DCHECK(segment.active);
+      // Segments of size == 0 are just nops.
+      if (size == 0) continue;
+
+      uint32_t dest_offset = EvalUint32InitExpr(instance, segment.dest_addr);
+      DCHECK(IsInBounds(dest_offset, size, instance->memory_size()));
+      byte* dest = instance->memory_start() + dest_offset;
+      const byte* src = wire_bytes.start() + segment.source.offset();
+      memcpy(dest, src, size);
+    }
   }
 }
 
@@ -1539,7 +1566,17 @@ void InstanceBuilder::LoadTableSegments(Handle<WasmInstanceObject> instance) {
                    instance->tables()->get(elem_segment.table_index)),
                isolate_),
         elem_segment, dst, src, count);
-    CHECK(success);
+    if (enabled_.bulk_memory) {
+      if (!success) {
+        thrower_->LinkError("table initializer is out of bounds");
+        // Break out instead of returning; we don't want to continue to
+        // initialize any further element segments, but still need to add
+        // dispatch tables below.
+        break;
+      }
+    } else {
+      CHECK(success);
+    }
   }
 
   int table_count = static_cast<int>(module_->tables.size());

test/mjsunit/wasm/bulk-memory.js

@@ -165,3 +165,74 @@ function getMemoryFill(mem) {
   const instance = builder.instantiate();
   assertTraps(kTrapElemSegmentDropped, () => instance.exports.drop());
 })();
+
+(function TestLazyDataSegmentBoundsCheck() {
+  const memory = new WebAssembly.Memory({initial: 1});
+  const view = new Uint8Array(memory.buffer);
+  const builder = new WasmModuleBuilder();
+  builder.addImportedMemory('m', 'memory', 1);
+  builder.addDataSegment(kPageSize - 1, [42, 42]);
+  builder.addDataSegment(0, [111, 111]);
+
+  assertEquals(0, view[kPageSize - 1]);
+
+  // Instantiation fails, but still modifies memory.
+  assertThrows(() => builder.instantiate({m: {memory}}), WebAssembly.LinkError);
+
+  assertEquals(42, view[kPageSize - 1]);
+  // The second segment is not initialized.
+  assertEquals(0, view[0]);
+})();
+
+(function TestLazyElementSegmentBoundsCheck() {
+  const table = new WebAssembly.Table({initial: 3, element: 'anyfunc'});
+  const builder = new WasmModuleBuilder();
+  builder.addImportedTable('m', 'table', 1);
+  const f = builder.addFunction('f', kSig_i_v).addBody([kExprI32Const, 42]);
+
+  const tableIndex = 0;
+  const isGlobal = false;
+  const isImport = true;
+  builder.addElementSegment(
+      tableIndex, 2, isGlobal, [f.index, f.index], isImport);
+  builder.addElementSegment(
+      tableIndex, 0, isGlobal, [f.index, f.index], isImport);
+
+  assertEquals(null, table.get(0));
+  assertEquals(null, table.get(1));
+  assertEquals(null, table.get(2));
+
+  // Instantiation fails, but still modifies the table.
+  assertThrows(() => builder.instantiate({m: {table}}), WebAssembly.LinkError);
+
+  // The second segment is not initialized.
+  assertEquals(null, table.get(0));
+  assertEquals(null, table.get(1));
+  assertEquals(42, table.get(2)());
+})();
+
+(function TestLazyDataAndElementSegments() {
+  const table = new WebAssembly.Table({initial: 1, element: 'anyfunc'});
+  const memory = new WebAssembly.Memory({initial: 1});
+  const view = new Uint8Array(memory.buffer);
+  const builder = new WasmModuleBuilder();
+
+  builder.addImportedMemory('m', 'memory', 1);
+  builder.addImportedTable('m', 'table', 1);
+  const f = builder.addFunction('f', kSig_i_v).addBody([kExprI32Const, 42]);
+
+  const tableIndex = 0;
+  const isGlobal = false;
+  const isImport = true;
+  builder.addElementSegment(
+      tableIndex, 0, isGlobal, [f.index, f.index], isImport);
+  builder.addDataSegment(0, [42]);
+
+  // Instantiation fails, but still modifies the table. The memory is not
+  // modified, since data segments are initialized after element segments.
+  assertThrows(
+      () => builder.instantiate({m: {memory, table}}), WebAssembly.LinkError);
+
+  assertEquals(42, table.get(0)());
+  assertEquals(0, view[0]);
+})();

test/mjsunit/wasm/wasm-module-builder.js

@@ -898,12 +898,18 @@ class WasmModuleBuilder {
     }
     this.element_segments.push({table: table, base: base, is_global: is_global,
                                     array: array, is_active: true});
-    if (!is_global) {
+
+    // As a testing convenience, update the table length when adding an element
+    // segment. If the table is imported, we can't do this because we don't
+    // know how long the table actually is. If |is_global| is true, then the
+    // base is a global index, instead of an integer offset, so we can't update
+    // the table then either.
+    if (!(is_import || is_global)) {
       var length = base + array.length;
-      if (!is_import && length > this.tables[0].initial_size) {
+      if (length > this.tables[0].initial_size) {
         this.tables[0].initial_size = length;
       }
-      if (!is_import && this.tables[0].has_max &&
+      if (this.tables[0].has_max &&
           length > this.tables[0].max_size) {
         this.tables[0].max_size = length;
       }

test/wasm-spec-tests/wasm-spec-tests.status

@@ -6,6 +6,10 @@
 [ALWAYS, {
   #TODO(ahaas): Add additional stack checks on mips.
   'tests/skip-stack-guard-page': [PASS, ['arch == mipsel or arch == mips64el or ((arch == ppc or arch == ppc64 or arch == s390 or arch == s390x) and simulator_run)', SKIP]],
+  # TODO(v8:9144): The MVP behavior when bounds-checking segments changed in
+  # the bulk-memory proposal. Since we've enabled bulk-memory by default, we
+  # need to update to use its testsuite.
+  'tests/linking': [FAIL],
 }],  # ALWAYS
 
 ['arch == mipsel or arch == mips64el or arch == mips or arch == mips64', {