2 above disk disk bytecode core api bytecode class

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Unformatted text preview: Bytecode Java 2 model (SDK 1.2 & above) Disk Disk Bytecode Core API bytecode Class loader Internet Internet Bytecode Class loader Class object Verifier JVM SY32 Secure Computing, Lecture 16 6 Class Loaders & Security • Bytecode with different origins is loaded by Bytecode different class loader objects different • JVM identifies a class by name and class loader JVM and Prevents, e.g., hostile applet from substituting its Prevents, java.net.Socket class for real one java.net.Socket • Difficult to implement correctly; bugs found in March & May 1996 July 1998 November 2000 SY32 Secure Computing, Lecture 16 7 Bytecode Verification • Verifier looks for .class file format violations Abuse of final modifier Abuse final Classes that don't have one superclass Illegal data conversions Operand stack overflow or underflow • Field and method access checking is delayed Field until runtime, then performed once only until SY32 Secure Computing, Lecture 16 8 Code Validation in .NET • Managed code is organized as logical units Managed called assemblies, containing CIL instructions, assemblies containing metadata and resources metadata • Validation checks that Files have correct format (PE/COFF) Metadata are present and uncorrupted CIL instructions are legal SY32 Secure Comput...
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