Bug 175693 – WebAssembly: const in unreachable code decoded incorrectly, erroneously rejects binary as invalid

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Alon Zakai]

Created attachment 318433 [details]
js script

Running

jsc b.js -- b.wasm

it reports

Exception: Error: WebAssembly.Module doesn't parse at byte 287 / 321: can't get immediate for I64Const in unreachable context, in function at index 0 (evaluating 'new WebAssembly.Module(binary)')
Module@[native code]
global [e-mail]:22:63

However the wasm binary is valid (accepted by v8, sm, binaryen, wabt).

[Radar WebKit Bug Importer]

<rdar://problem/33952443>

[Alon Zakai]

Created attachment 318434 [details]
wasm file

[JF Bastien]

I believe this is a benign bug because unreachable code shouldn't occur anyways. It's still a bug we should fix, though.

[JF Bastien]

It looks like the i64.const causing the issue is:

    42 80 80 80 80 80 80 80 80 80 |       i64.const -9223372036854775808

[JF Bastien]

Well this is our bug:

    // one immediate cases
    case I32Const:
    case I64Const: // <------ derp
    case SetLocal:
    case GetLocal:
    case TeeLocal:
    case GetGlobal:
    case SetGlobal:
    case Br:
    case BrIf:
    case Call: {
        uint32_t unused;
        WASM_PARSER_FAIL_IF(!parseVarUInt32(unused), "can't get immediate for ", m_currentOpcode, " in unreachable context");
        return { };
    }



This is benign, not a security issue.

[JF Bastien]

Created attachment 318440 [details]
patch

[Saam Barati]

Comment on attachment 318440 [details]
patch

please add test

[JF Bastien]

Created attachment 318443 [details]
patch

Add test, and also handle i32.const / i64.const as signed.

[WebKit Commit Bot]

Comment on attachment 318443 [details]
patch

Rejecting attachment 318443 [details] from commit-queue.

Failed to run "['/Volumes/Data/EWS/WebKit/Tools/Scripts/webkit-patch', '--status-host=webkit-queues.webkit.org', '--bot-id=webkit-cq-02', 'validate-changelog', '--check-oops', '--non-interactive', 318443, '--port=mac']" exit_code: 1 cwd: /Volumes/Data/EWS/WebKit

ChangeLog entry in JSTests/ChangeLog contains OOPS!.

Full output: http://webkit-queues.webkit.org/results/4333352

[JF Bastien]

Created attachment 318444 [details]
patch

Fix OOPS.

[WebKit Commit Bot]

The commit-queue encountered the following flaky tests while processing attachment 318444 [details]:

svg/animations/smil-leak-list-property-instances.svg bug 175701 (author: [e-mail])
The commit-queue is continuing to process your patch.

[WebKit Commit Bot]

Comment on attachment 318444 [details]
patch

Clearing flags on attachment: 318444

Committed r220894: <http://trac.webkit.org/changeset/220894>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.