001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 * 017 */ 018package org.apache.bcel.verifier.statics; 019 020 021import org.apache.bcel.Repository; 022import org.apache.bcel.classfile.ClassFormatException; 023import org.apache.bcel.classfile.JavaClass; 024import org.apache.bcel.verifier.PassVerifier; 025import org.apache.bcel.verifier.VerificationResult; 026import org.apache.bcel.verifier.Verifier; 027import org.apache.bcel.verifier.exc.LoadingException; 028import org.apache.bcel.verifier.exc.Utility; 029 030/** 031 * This PassVerifier verifies a class file according to pass 1 as 032 * described in The Java Virtual Machine Specification, 2nd edition. 033 * More detailed information is to be found at the do_verify() method's 034 * documentation. 035 * 036 * @see #do_verify() 037 */ 038public final class Pass1Verifier extends PassVerifier{ 039 /** 040 * DON'T USE THIS EVEN PRIVATELY! USE getJavaClass() INSTEAD. 041 * @see #getJavaClass() 042 */ 043 private JavaClass jc; 044 045 /** 046 * The Verifier that created this. 047 */ 048 private final Verifier myOwner; 049 050 /** 051 * Used to load in and return the myOwner-matching JavaClass object when needed. 052 * Avoids loading in a class file when it's not really needed! 053 */ 054 private JavaClass getJavaClass() { 055 if (jc == null) { 056 try { 057 jc = Repository.lookupClass(myOwner.getClassName()); 058 } catch (final ClassNotFoundException e) { 059 // FIXME: currently, Pass1Verifier treats jc == null as a special 060 // case, so we don't need to do anything here. A better solution 061 // would be to simply throw the ClassNotFoundException 062 // out of this method. 063 } 064 } 065 return jc; 066 } 067 068 /** 069 * Should only be instantiated by a Verifier. 070 * 071 * @see Verifier 072 */ 073 public Pass1Verifier(final Verifier owner) { 074 myOwner = owner; 075 } 076 077 /** 078 * Pass-one verification basically means loading in a class file. 079 * The Java Virtual Machine Specification is not too precise about 080 * what makes the difference between passes one and two. 081 * The answer is that only pass one is performed on a class file as 082 * long as its resolution is not requested; whereas pass two and 083 * pass three are performed during the resolution process. 084 * Only four constraints to be checked are explicitly stated by 085 * The Java Virtual Machine Specification, 2nd edition: 086 * <UL> 087 * <LI>The first four bytes must contain the right magic number (0xCAFEBABE). 088 * <LI>All recognized attributes must be of the proper length. 089 * <LI>The class file must not be truncated or have extra bytes at the end. 090 * <LI>The constant pool must not contain any superficially unrecognizable information. 091 * </UL> 092 * A more in-depth documentation of what pass one should do was written by 093 * <A HREF=mailto:pwfong@cs.sfu.ca>Philip W. L. Fong</A>: 094 * <UL> 095 * <LI> the file should not be truncated. 096 * <LI> the file should not have extra bytes at the end. 097 * <LI> all variable-length structures should be well-formatted: 098 * <UL> 099 * <LI> there should only be constant_pool_count-1 many entries in the constant pool. 100 * <LI> all constant pool entries should have size the same as indicated by their type tag. 101 * <LI> there are exactly interfaces_count many entries in the interfaces array of the class file. 102 * <LI> there are exactly fields_count many entries in the fields array of the class file. 103 * <LI> there are exactly methods_count many entries in the methods array of the class file. 104 * <LI> there are exactly attributes_count many entries in the attributes array of the class file, 105 * fields, methods, and code attribute. 106 * <LI> there should be exactly attribute_length many bytes in each attribute. 107 * Inconsistency between attribute_length and the actually size of the attribute content should be uncovered. 108 * For example, in an Exceptions attribute, the actual number of exceptions as required by the number_of_exceptions field 109 * might yeild an attribute size that doesn't match the attribute_length. Such an anomaly should be detected. 110 * <LI> all attributes should have proper length. In particular, under certain context (e.g. while parsing method_info), 111 * recognizable attributes (e.g. "Code" attribute) should have correct format (e.g. attribute_length is 2). 112 * </UL> 113 * <LI> Also, certain constant values are checked for validity: 114 * <UL> 115 * <LI> The magic number should be 0xCAFEBABE. 116 * <LI> The major and minor version numbers are valid. 117 * <LI> All the constant pool type tags are recognizable. 118 * <LI> All undocumented access flags are masked off before use. Strictly speaking, this is not really a check. 119 * <LI> The field this_class should point to a string that represents a legal non-array class name, 120 * and this name should be the same as the class file being loaded. 121 * <LI> the field super_class should point to a string that represents a legal non-array class name. 122 * <LI> Because some of the above checks require cross referencing the constant pool entries, 123 * guards are set up to make sure that the referenced entries are of the right type and the indices 124 * are within the legal range (0 < index < constant_pool_count). 125 * </UL> 126 * <LI> Extra checks done in pass 1: 127 * <UL> 128 * <LI> the constant values of static fields should have the same type as the fields. 129 * <LI> the number of words in a parameter list does not exceed 255 and locals_max. 130 * <LI> the name and signature of fields and methods are verified to be of legal format. 131 * </UL> 132 * </UL> 133 * (From the Paper <A HREF="http://www.cs.sfu.ca/people/GradStudents/pwfong/personal/JVM/pass1/"> 134 * The Mysterious Pass One, first draft, September 2, 1997</A>.) 135 * 136 * <P>However, most of this is done by parsing a class file or generating a class file into BCEL's internal data structure. 137 * <B>Therefore, all that is really done here is look up the class file from BCEL's repository.</B> 138 * This is also motivated by the fact that some omitted things 139 * (like the check for extra bytes at the end of the class file) are handy when actually using BCEL to repair a class file 140 * (otherwise you would not be able to load it into BCEL).</P> 141 * 142 * @see org.apache.bcel.Repository 143 * @see org.apache.bcel.Const#JVM_CLASSFILE_MAGIC 144 */ 145 @Override 146 public VerificationResult do_verify() { 147 JavaClass jc; 148 try{ 149 jc = getJavaClass(); //loads in the class file if not already done. 150 151 if (jc != null) { 152 /* If we find more constraints to check, we should do this in an own method. */ 153 if (! myOwner.getClassName().equals(jc.getClassName())) { 154 // This should maybe caught by BCEL: In case of renamed .class files we get wrong 155 // JavaClass objects here. 156 throw new LoadingException("Wrong name: the internal name of the .class file '"+jc.getClassName()+ 157 "' does not match the file's name '"+myOwner.getClassName()+"'."); 158 } 159 } 160 161 } 162 catch(final LoadingException e) { 163 return new VerificationResult(VerificationResult.VERIFIED_REJECTED, e.getMessage()); 164 } 165 catch(final ClassFormatException e) { 166 return new VerificationResult(VerificationResult.VERIFIED_REJECTED, e.getMessage()); 167 } 168 catch(final RuntimeException e) { 169 // BCEL does not catch every possible RuntimeException; e.g. if 170 // a constant pool index is referenced that does not exist. 171 return new VerificationResult(VerificationResult.VERIFIED_REJECTED, "Parsing via BCEL did not succeed. "+ 172 e.getClass().getName()+" occured:\n"+Utility.getStackTrace(e)); 173 } 174 175 if (jc != null) { 176 return VerificationResult.VR_OK; 177 } 178 //TODO: Maybe change Repository's behavior to throw a LoadingException instead of just returning "null" 179 // if a class file cannot be found or in another way be looked up. 180 return new VerificationResult(VerificationResult.VERIFIED_REJECTED, "Repository.lookup() failed. FILE NOT FOUND?"); 181 } 182 183 /** 184 * Currently this returns an empty array of String. 185 * One could parse the error messages of BCEL 186 * (written to java.lang.System.err) when loading 187 * a class file such as detecting unknown attributes 188 * or trailing garbage at the end of a class file. 189 * However, Markus Dahm does not like the idea so this 190 * method is currently useless and therefore marked as 191 * <B>TODO</B>. 192 */ 193 @Override 194 public String[] getMessages() { 195 // This method is only here to override the javadoc-comment. 196 return super.getMessages(); 197 } 198 199}