Bug 289890 – [WASM] SEGV in B3 ReduceStrength Optimization During Shl/SExt32 IR Node Handling

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

Created attachment 474590 [details]
simplified poc

# What is required to reproduce the issue?
My environment:
Ubuntu 22.04.2 LTS
https://github.com/WebKit/WebKit.git
ec5c28c0e698b3cd3c028f50141923a95a29dcde

# Summary

A vulnerability has been identified in the JavaScriptCore engine where executing certain WebAssembly code causes a crash due to a null pointer dereference in the reduceValueStrength() function of B3ReduceStrength.cpp. Specifically, the optimizer fails to check for null pointers when accessing child nodes, leading to a segmentation fault at address 0x000000000030. This issue can be remotely triggered by specially crafted WebAssembly code, posing a security risk as it may allow attackers to crash the application or potentially execute arbitrary code.

# Steps to reproduce
1. **Execute the PoC:**

   ```bash
   ./jsc ./poc.js
   ```

# Expected results

Exit normally.

# Actual results

JavaScriptCore crashed with a segmentation fault:

```
AddressSanitizer:DEADLYSIGNAL
=================================================================
==2011591==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000030 (pc 0x56203613413f bp 0x7f66baaedb70 sp 0x7f66baaed6a0 T2)
==2011591==The signal is caused by a READ memory access.
==2011591==Hint: address points to the zero page.
    #0 0x56203613413f in JSC::B3::(anonymous namespace)::ReduceStrength::reduceValueStrength() /data/workspace/WebKit/Source/JavaScriptCore/b3/B3ReduceStrength.cpp:2043:101
    #1 0x56203610fb69 in JSC::B3::(anonymous namespace)::ReduceStrength::run() /data/workspace/WebKit/Source/JavaScriptCore/b3/B3ReduceStrength.cpp:548:21
    #2 0x56203610fb69 in JSC::B3::reduceStrength(JSC::B3::Procedure&) /data/workspace/WebKit/Source/JavaScriptCore/b3/B3ReduceStrength.cpp:3861:27
    #3 0x5620360eb762 in JSC::B3::generateToAir(JSC::B3::Procedure&) /data/workspace/WebKit/Source/JavaScriptCore/b3/B3Generate.cpp:86:9
    #4 0x5620360eb316 in JSC::B3::prepareForGeneration(JSC::B3::Procedure&) /data/workspace/WebKit/Source/JavaScriptCore/b3/B3Generate.cpp:60:5
    #5 0x562038ec14c5 in JSC::Wasm::parseAndCompileOMG(JSC::Wasm::CompilationContext&, JSC::Wasm::OptimizingJITCallee&, JSC::Wasm::FunctionData const&, JSC::Wasm::TypeDefinition const&, WTF::Vector<JSC::Wasm::UnlinkedWasmToWasmCall, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc>&, JSC::Wasm::CalleeGroup&, JSC::Wasm::ModuleInformation const&, JSC::MemoryMode, JSC::Wasm::CompilationMode, JSC::Wasm::FunctionCodeIndex, std::optional<bool>, unsigned int) /data/workspace/WebKit/Source/JavaScriptCore/wasm/WasmOMGIRGenerator.cpp:5840:9
    #6 0x562038ee78bf in JSC::Wasm::OMGPlan::work() /data/workspace/WebKit/Source/JavaScriptCore/wasm/WasmOMGPlan.cpp:138:34
    #7 0x562039192b0a in JSC::Wasm::Worklist::Thread::work() /data/workspace/WebKit/Source/JavaScriptCore/wasm/WasmWorklist.cpp:114:15
    #8 0x5620395aa56a in WTF::AutomaticThread::start(WTF::AbstractLocker const&)::$_0::operator()() const /data/workspace/WebKit/Source/WTF/wtf/AutomaticThread.cpp:225:37
    #9 0x5620395aa56a in WTF::Detail::CallableWrapper<WTF::AutomaticThread::start(WTF::AbstractLocker const&)::$_0, void>::call() /data/workspace/WebKit/Source/WTF/wtf/Function.h:53:39
    #10 0x5620396390cb in WTF::Function<void ()>::operator()() const /data/workspace/WebKit/Source/WTF/wtf/Function.h:82:35
    #11 0x5620396390cb in WTF::Thread::entryPoint(WTF::Thread::NewThreadContext*) /data/workspace/WebKit/Source/WTF/wtf/Threading.cpp:268:5
    #12 0x5620399d9ed3 in WTF::wtfThreadEntryPoint(void*) /data/workspace/WebKit/Source/WTF/wtf/posix/ThreadingPOSIX.cpp:241:5
    #13 0x562033953558 in asan_thread_start(void*) crtstuff.c
    #14 0x7f6706df0ac2  (/lib/x86_64-linux-gnu/libc.so.6+0x94ac2) (BuildId: cd410b710f0f094c6832edd95931006d883af48e)
    #15 0x7f6706e8284f  (/lib/x86_64-linux-gnu/libc.so.6+0x12684f) (BuildId: cd410b710f0f094c6832edd95931006d883af48e)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /data/workspace/WebKit/Source/JavaScriptCore/b3/B3ReduceStrength.cpp:2043:101 in JSC::B3::(anonymous namespace)::ReduceStrength::reduceValueStrength()
```







# Credit
Xiangwei Zhang of Tencent Security YUNDING LAB

[Radar WebKit Bug Importer]

<rdar://problem/147210812>

Created attachment 474591 [details]
poc

[Yusuke Suzuki]

ToT issue, let's just fix it in ToT.

[Vassili Bykov]

Pull request: https://github.com/WebKit/WebKit/pull/43141

[EWS]

Committed 292876@main (9e460d82de2e): <https://commits.webkit.org/292876@main>

Reviewed commits have been landed. Closing PR #43141 and removing active labels.

[EWS]

Committed 289651.388@safari-7621-branch (1d355b86897b): <https://commits.webkit.org/289651.388@safari-7621-branch>

Reviewed commits have been landed. Closing PR #2940 and removing active labels.