1 files changed, 335 insertions, 0 deletions

diff --git a/js/src/wasm/WasmBinary.cpp b/js/src/wasm/WasmBinary.cpp
new file mode 100644
index 0000000000..ccf50f9d2d
--- /dev/null
+++ b/js/src/wasm/WasmBinary.cpp
@@ -0,0 +1,335 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ *
+ * Copyright 2021 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "wasm/WasmBinary.h"
+
+#include "js/Printf.h"
+#include "wasm/WasmValidate.h"
+
+using namespace js;
+using namespace js::wasm;
+
+// Decoder implementation.
+
+bool Decoder::failf(const char* msg, ...) {
+  va_list ap;
+  va_start(ap, msg);
+  UniqueChars str(JS_vsmprintf(msg, ap));
+  va_end(ap);
+  if (!str) {
+    return false;
+  }
+
+  return fail(str.get());
+}
+
+void Decoder::warnf(const char* msg, ...) {
+  if (!warnings_) {
+    return;
+  }
+
+  va_list ap;
+  va_start(ap, msg);
+  UniqueChars str(JS_vsmprintf(msg, ap));
+  va_end(ap);
+  if (!str) {
+    return;
+  }
+
+  (void)warnings_->append(std::move(str));
+}
+
+bool Decoder::fail(size_t errorOffset, const char* msg) {
+  MOZ_ASSERT(error_);
+  UniqueChars strWithOffset(JS_smprintf("at offset %zu: %s", errorOffset, msg));
+  if (!strWithOffset) {
+    return false;
+  }
+
+  *error_ = std::move(strWithOffset);
+  return false;
+}
+
+bool Decoder::readSectionHeader(uint8_t* id, SectionRange* range) {
+  if (!readFixedU8(id)) {
+    return false;
+  }
+
+  uint32_t size;
+  if (!readVarU32(&size)) {
+    return false;
+  }
+
+  range->start = currentOffset();
+  range->size = size;
+  return true;
+}
+
+bool Decoder::startSection(SectionId id, ModuleEnvironment* env,
+                           MaybeSectionRange* range, const char* sectionName) {
+  MOZ_ASSERT(!*range);
+
+  // Record state at beginning of section to allow rewinding to this point
+  // if, after skipping through several custom sections, we don't find the
+  // section 'id'.
+  const uint8_t* const initialCur = cur_;
+  const size_t initialCustomSectionsLength = env->customSections.length();
+
+  // Maintain a pointer to the current section that gets updated as custom
+  // sections are skipped.
+  const uint8_t* currentSectionStart = cur_;
+
+  // Only start a section with 'id', skipping any custom sections before it.
+
+  uint8_t idValue;
+  if (!readFixedU8(&idValue)) {
+    goto rewind;
+  }
+
+  while (idValue != uint8_t(id)) {
+    if (idValue != uint8_t(SectionId::Custom)) {
+      goto rewind;
+    }
+
+    // Rewind to the beginning of the current section since this is what
+    // skipCustomSection() assumes.
+    cur_ = currentSectionStart;
+    if (!skipCustomSection(env)) {
+      return false;
+    }
+
+    // Having successfully skipped a custom section, consider the next
+    // section.
+    currentSectionStart = cur_;
+    if (!readFixedU8(&idValue)) {
+      goto rewind;
+    }
+  }
+
+  // Don't check the size since the range of bytes being decoded might not
+  // contain the section body. (This is currently the case when streaming: the
+  // code section header is decoded with the module environment bytes, the
+  // body of the code section is streamed in separately.)
+
+  uint32_t size;
+  if (!readVarU32(&size)) {
+    goto fail;
+  }
+
+  range->emplace();
+  (*range)->start = currentOffset();
+  (*range)->size = size;
+  return true;
+
+rewind:
+  cur_ = initialCur;
+  env->customSections.shrinkTo(initialCustomSectionsLength);
+  return true;
+
+fail:
+  return failf("failed to start %s section", sectionName);
+}
+
+bool Decoder::finishSection(const SectionRange& range,
+                            const char* sectionName) {
+  if (resilientMode_) {
+    return true;
+  }
+  if (range.size != currentOffset() - range.start) {
+    return failf("byte size mismatch in %s section", sectionName);
+  }
+  return true;
+}
+
+bool Decoder::startCustomSection(const char* expected, size_t expectedLength,
+                                 ModuleEnvironment* env,
+                                 MaybeSectionRange* range) {
+  // Record state at beginning of section to allow rewinding to this point
+  // if, after skipping through several custom sections, we don't find the
+  // section 'id'.
+  const uint8_t* const initialCur = cur_;
+  const size_t initialCustomSectionsLength = env->customSections.length();
+
+  while (true) {
+    // Try to start a custom section. If we can't, rewind to the beginning
+    // since we may have skipped several custom sections already looking for
+    // 'expected'.
+    if (!startSection(SectionId::Custom, env, range, "custom")) {
+      return false;
+    }
+    if (!*range) {
+      goto rewind;
+    }
+
+    if (bytesRemain() < (*range)->size) {
+      goto fail;
+    }
+
+    CustomSectionEnv sec;
+    if (!readVarU32(&sec.nameLength) || sec.nameLength > bytesRemain()) {
+      goto fail;
+    }
+
+    sec.nameOffset = currentOffset();
+    sec.payloadOffset = sec.nameOffset + sec.nameLength;
+
+    uint32_t payloadEnd = (*range)->start + (*range)->size;
+    if (sec.payloadOffset > payloadEnd) {
+      goto fail;
+    }
+
+    sec.payloadLength = payloadEnd - sec.payloadOffset;
+
+    // Now that we have a valid custom section, record its offsets in the
+    // metadata which can be queried by the user via Module.customSections.
+    // Note: after an entry is appended, it may be popped if this loop or
+    // the loop in startSection needs to rewind.
+    if (!env->customSections.append(sec)) {
+      return false;
+    }
+
+    // If this is the expected custom section, we're done.
+    if (!expected || (expectedLength == sec.nameLength &&
+                      !memcmp(cur_, expected, sec.nameLength))) {
+      cur_ += sec.nameLength;
+      return true;
+    }
+
+    // Otherwise, blindly skip the custom section and keep looking.
+    skipAndFinishCustomSection(**range);
+    range->reset();
+  }
+  MOZ_CRASH("unreachable");
+
+rewind:
+  cur_ = initialCur;
+  env->customSections.shrinkTo(initialCustomSectionsLength);
+  return true;
+
+fail:
+  return fail("failed to start custom section");
+}
+
+void Decoder::finishCustomSection(const char* name, const SectionRange& range) {
+  MOZ_ASSERT(cur_ >= beg_);
+  MOZ_ASSERT(cur_ <= end_);
+
+  if (error_ && *error_) {
+    warnf("in the '%s' custom section: %s", name, error_->get());
+    skipAndFinishCustomSection(range);
+    return;
+  }
+
+  uint32_t actualSize = currentOffset() - range.start;
+  if (range.size != actualSize) {
+    if (actualSize < range.size) {
+      warnf("in the '%s' custom section: %" PRIu32 " unconsumed bytes", name,
+            uint32_t(range.size - actualSize));
+    } else {
+      warnf("in the '%s' custom section: %" PRIu32
+            " bytes consumed past the end",
+            name, uint32_t(actualSize - range.size));
+    }
+    skipAndFinishCustomSection(range);
+    return;
+  }
+
+  // Nothing to do! (c.f. skipAndFinishCustomSection())
+}
+
+void Decoder::skipAndFinishCustomSection(const SectionRange& range) {
+  MOZ_ASSERT(cur_ >= beg_);
+  MOZ_ASSERT(cur_ <= end_);
+  cur_ = (beg_ + (range.start - offsetInModule_)) + range.size;
+  MOZ_ASSERT(cur_ <= end_);
+  clearError();
+}
+
+bool Decoder::skipCustomSection(ModuleEnvironment* env) {
+  MaybeSectionRange range;
+  if (!startCustomSection(nullptr, 0, env, &range)) {
+    return false;
+  }
+  if (!range) {
+    return fail("expected custom section");
+  }
+
+  skipAndFinishCustomSection(*range);
+  return true;
+}
+
+bool Decoder::startNameSubsection(NameType nameType,
+                                  Maybe<uint32_t>* endOffset) {
+  MOZ_ASSERT(!*endOffset);
+
+  const uint8_t* const initialPosition = cur_;
+
+  uint8_t nameTypeValue;
+  if (!readFixedU8(&nameTypeValue)) {
+    goto rewind;
+  }
+
+  if (nameTypeValue != uint8_t(nameType)) {
+    goto rewind;
+  }
+
+  uint32_t payloadLength;
+  if (!readVarU32(&payloadLength) || payloadLength > bytesRemain()) {
+    return fail("bad name subsection payload length");
+  }
+
+  *endOffset = Some(currentOffset() + payloadLength);
+  return true;
+
+rewind:
+  cur_ = initialPosition;
+  return true;
+}
+
+bool Decoder::finishNameSubsection(uint32_t endOffset) {
+  uint32_t actual = currentOffset();
+  if (endOffset != actual) {
+    return failf("bad name subsection length (endOffset: %" PRIu32
+                 ", actual: %" PRIu32 ")",
+                 endOffset, actual);
+  }
+
+  return true;
+}
+
+bool Decoder::skipNameSubsection() {
+  uint8_t nameTypeValue;
+  if (!readFixedU8(&nameTypeValue)) {
+    return fail("unable to read name subsection id");
+  }
+
+  switch (nameTypeValue) {
+    case uint8_t(NameType::Module):
+    case uint8_t(NameType::Function):
+      return fail("out of order name subsections");
+    default:
+      break;
+  }
+
+  uint32_t payloadLength;
+  if (!readVarU32(&payloadLength) || !readBytes(payloadLength)) {
+    return fail("bad name subsection payload length");
+  }
+
+  return true;
+}