Add support for loading and verifying signed Wasm modules.

Signed-off-by: Piotr Sikora <[email protected]>

Author: PiotrSikora

src/v8/v8.cc

@@ -15,6 +15,7 @@
 
 #include "include/proxy-wasm/v8.h"
 
+#include <array>
 #include <cassert>
 #include <iomanip>
 #include <memory>
@@ -25,11 +26,39 @@
 #include <utility>
 #include <vector>
 
+#include <openssl/curve25519.h>
+#include <openssl/sha.h>
+
 #include "v8.h"
 #include "v8-version.h"
 #include "wasm-api/wasm.hh"
 
 namespace proxy_wasm {
+
+#ifdef PROXY_WASM_VERIFY_WITH_ED25519_PUBKEY
+
+static uint8_t hex2dec(const unsigned char c) {
+  if (c >= '0' && c <= '9') {
+    return c - '0';
+  } else if (c >= 'a' && c <= 'f') {
+    return c - 'a' + 10;
+  } else if (c >= 'A' && c <= 'F') {
+    return c - 'A' + 10;
+  } else {
+    throw std::logic_error{"invalid hex character"};
+  }
+}
+
+template <size_t N> constexpr std::array<uint8_t, N> hex2pubkey(const char (&hex)[2 * N + 1]) {
+  std::array<uint8_t, N> pubkey;
+  for (size_t i = 0; i < pubkey.size(); i++) {
+    pubkey[i] = hex2dec(hex[2 * i]) << 4 | hex2dec(hex[2 * i + 1]);
+  }
+  return pubkey;
+}
+
+#endif
+
 namespace {
 
 wasm::Engine *engine() {
@@ -94,6 +123,7 @@ class V8 : public WasmVm {
 #undef _GET_MODULE_FUNCTION
 
 private:
+  bool verifySignature();
   void buildFunctionNameIndex();
   wasm::vec<byte_t> getStrippedSource();
   std::string getFailMessage(std::string_view function_name, wasm::own<wasm::Trap> trap);
@@ -279,6 +309,8 @@ bool V8::load(const std::string &code, bool allow_precompiled) {
   source_ = wasm::vec<byte_t>::make_uninitialized(code.size());
   ::memcpy(source_.get(), code.data(), code.size());
 
+  verifySignature();
+
   if (allow_precompiled) {
     const auto section_name = getPrecompiledSectionName();
     if (!section_name.empty()) {
@@ -312,6 +344,66 @@ bool V8::load(const std::string &code, bool allow_precompiled) {
   return module_ != nullptr;
 }
 
+bool V8::verifySignature() {
+#ifdef PROXY_WASM_VERIFY_WITH_ED25519_PUBKEY
+  /*
+   * Ed25519 signature generated using https://github.com/jedisct1/wasmsign
+   */
+
+  auto payload = getCustomSection("signature_wasmsign");
+  if (payload.empty()) {
+    fail(FailState::UnableToInitializeCode, "Custom Section \"signature_wasmsign\" not found");
+    return false;
+  }
+
+  if (source_.get() + source_.size() != payload.data() + payload.size()) {
+    fail(FailState::UnableToInitializeCode,
+         "Custom Section \"signature_wasmsign\" not at the end of Wasm module");
+    return false;
+  }
+
+  if (payload.size() != 68) {
+    fail(FailState::UnableToInitializeCode,
+         "Custom Section \"signature_wasmsign\" contains paylod of a wrong size "
+         "(want: 68, is: " +
+             std::to_string(payload.size()) + ")");
+    return false;
+  }
+
+  uint32_t alg_id;
+  std::memcpy(&alg_id, payload.data(), sizeof(uint32_t));
+
+  if (alg_id != 2) {
+    fail(FailState::UnableToInitializeCode,
+         "Signature has a wrong alg_id (want: 2, is: " + std::to_string(alg_id) + ")");
+    return false;
+  }
+
+  const auto *signature = reinterpret_cast<const uint8_t *>(payload.data()) + sizeof(uint32_t);
+
+  SHA512_CTX ctx;
+  SHA512_Init(&ctx);
+  SHA512_Update(&ctx, "WasmSignature", sizeof("WasmSignature") - 1);
+  const uint32_t ad_len = 0;
+  SHA512_Update(&ctx, &ad_len, sizeof(uint32_t));
+  const size_t section_len = 3 + sizeof("signature_wasmsign") - 1 + 68;
+  SHA512_Update(&ctx, source_.get(), source_.size() - section_len);
+  uint8_t hash[SHA512_DIGEST_LENGTH];
+  SHA512_Final(hash, &ctx);
+
+  static const auto ed25519_pubkey = hex2pubkey<32>(PROXY_WASM_VERIFY_WITH_ED25519_PUBKEY);
+
+  if (!ED25519_verify(hash, sizeof(hash), signature, ed25519_pubkey.data())) {
+    fail(FailState::UnableToInitializeCode, "Signature mismatch");
+    return false;
+  }
+
+  integration()->trace("Wasm signature OK (Ed25519)");
+#endif
+
+  return true;
+}
+
 void V8::buildFunctionNameIndex() {
   // build function index -> function name map for backtrace
   // https://webassembly.github.io/spec/core/appendix/custom.html#binary-namesubsection