[tbb-bugs] #21549 [Applications/Tor Browser]: Investigate wasm for linkability/fingerprintability/disk avoidance issues

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#21549: Investigate wasm for linkability/fingerprintability/disk avoidance issues
-------------------------------------------------+-------------------------
 Reporter:  gk                                   |          Owner:  tbb-
                                                 |  team
     Type:  task                                 |         Status:  new
 Priority:  Very High                            |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  ff68-esr, tbb-9.0,                   |  Actual Points:
  TorBrowserTeam201910                           |
Parent ID:                                       |         Points:  1
 Reviewer:                                       |        Sponsor:
                                                 |  Sponsor44-can
-------------------------------------------------+-------------------------

Comment (by sysrqb):

 The WebAssembly API [https://developer.mozilla.org/en-US/docs/WebAssembly
 consists] of:
  - The [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly WebAssembly]
 Object:
    - [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/compile
 WebAssembly.compile()]
    - [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/compileStreaming
 WebAssembly.compileStreaming()]
    - [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/instantiate
 WebAssembly.instantiate()]
    - [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/instantiateStreaming
 WebAssembly.instantiateStreaming()]
    - [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/validate
 WebAssembly.validate()]
  - The [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Global
 WebAssembly.Global] Object:
  - The [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Module
 WebAssembly.Module] Object:
  - The [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance
 WebAssembly.Instance] Object:
  - The [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Memory
 WebAssembly.Memory] Object:
    - [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Memory/buffer
 WebAssembly.Memory().buffer()]
  - The [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Table
 WebAssembly.Table] Object:
  - The [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/CompileError
 WebAssembly.CompileError] Object:
  - The [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/LinkError
 WebAssembly.LinkError] Object:
  - The [https://developer.mozilla.org/en-
 US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/RuntimeError
 WebAssembly.RuntimeError] Object:

 These are [https://searchfox.org/mozilla-
 esr68/source/js/src/wasm/WasmJS.cpp#3670 exported] and implemented:
 [https://searchfox.org/mozilla-esr68/source/js/src/wasm/WasmJS.cpp#2997
 WebAssembly.compile()]
 [https://searchfox.org/mozilla-esr68/source/js/src/wasm/WasmJS.cpp#3618
 WebAssembly.compileStreaming()]
 [https://searchfox.org/mozilla-esr68/source/js/src/wasm/WasmJS.cpp#3046
 WebAssembly.instantiate()]
 [https://searchfox.org/mozilla-esr68/source/js/src/wasm/WasmJS.cpp#3641
 WebAssembly.instantiateStreaming()]
 [https://searchfox.org/mozilla-esr68/source/js/src/wasm/WasmJS.cpp#3091
 WebAssembly.validate()]
 [https://searchfox.org/mozilla-esr68/source/js/src/wasm/WasmJS.cpp#2342
 WebAssembly.Global]
 [https://searchfox.org/mozilla-esr68/source/js/src/wasm/WasmJS.cpp#1587
 WebAssembly.Memory]
 [https://searchfox.org/mozilla-esr68/source/js/src/wasm/WasmJS.cpp#657
 WebAssembly.Module]
 [https://searchfox.org/mozilla-esr68/source/js/src/wasm/WasmJS.cpp#1169
 WebAssembly.Instance]
 [https://searchfox.org/mozilla-esr68/source/js/src/wasm/WasmJS.cpp#1926
 WebAssembly.Table]

 - `WebAssembly.compile` is for ahead-of-time compiling a WASM module. It
 takes in a buffer of WASM and returns a Promise of a `WebAssembly.Module`.
 - `WebAssembly.compileStreaming` is similar to `compile()` except it takes
 in a Response object or Promise for a wasm module (compared with a buffer
 containing the module).
 - `WebAssembly.instantiate` has two prototypes.
   - The first takes in a buffer of WASM and returns a Promise of a tuple:
 (`WebAssembly.Module`, `WebAssembly.Instance`). The `Module` is the
 compiled WASM, and the `Instance` is an instantiation of that `Module`.
   - The second takes in an existing `WebAssembly.Module` (already compiled
 WASM) and returns an `Instance`.
 - `WebAssembly.instantiateStreaming` takes in a a Response object or
 Promise (like `compileStreaming`) and returns a Promise of a tuple:
 (`WebAssembly.Module`, `WebAssembly.Instance`) like `instantiate()`.
 - `WebAssembly.validate()` takes in a buffer of WASM binary code and
 returns a boolean true if the buffer contained valid wasm, and false
 otherwise.

 - `WebAssembly.Global` is an object containing a WASM "global" variable.
 Multiple `Global` instances may be passed into
 `WebAssembly.instantiate()`, but these globals are only accessible by WASM
 if they are explicitly "imported" by the WASM Module.
 - `WebAssembly.Instance` is an instance of a `Module` initialized with
 `Global` and/or `Memory` instances.
 - `WebAssembly.Memory().buffer` is an ArrayBuffer representing the "heap"
 memory available in the WASM module. This is readable and writable by both
 JavaScript and WASM. From WASM, pointers are represented by an
 [https://emscripten.org/docs/porting/emscripten-runtime-environment.html
 #emscripten-memory-representation index] of the Memory ArrayBuffer.
 - `WebAssembly.Table` is an "array-like" structure storing function-
 references. In the future, Tables may store more than only function-
 references. Tables allow calling arbitrary functions from WASM (after the
 WASM module assigns a function-reference at an index in the table). It
 seems like this provides a level of abstraction compared with exporting a
 function from WASM into JavaScript, because function-references can be
 added/deleted/modified in the Table at run-time.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21549#comment:31>
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