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 * @version $Id: Pass1Verifier.java 1806200 2017-08-25 16:33:06Z ggregory $
037 * @see #do_verify()
038 */
039public final class Pass1Verifier extends PassVerifier{
040    /**
041     * DON'T USE THIS EVEN PRIVATELY! USE getJavaClass() INSTEAD.
042     * @see #getJavaClass()
043     */
044    private JavaClass jc;
045
046    /**
047     * The Verifier that created this.
048     */
049    private final Verifier myOwner;
050
051    /**
052     * Used to load in and return the myOwner-matching JavaClass object when needed.
053     * Avoids loading in a class file when it's not really needed!
054     */
055    private JavaClass getJavaClass() {
056        if (jc == null) {
057            try {
058                jc = Repository.lookupClass(myOwner.getClassName());
059            } catch (final ClassNotFoundException e) {
060                // FIXME: currently, Pass1Verifier treats jc == null as a special
061                // case, so we don't need to do anything here.  A better solution
062                // would be to simply throw the ClassNotFoundException
063                // out of this method.
064            }
065        }
066        return jc;
067    }
068
069    /**
070     * Should only be instantiated by a Verifier.
071     *
072     * @see Verifier
073     */
074    public Pass1Verifier(final Verifier owner) {
075        myOwner = owner;
076    }
077
078    /**
079     * Pass-one verification basically means loading in a class file.
080     * The Java Virtual Machine Specification is not too precise about
081     * what makes the difference between passes one and two.
082     * The answer is that only pass one is performed on a class file as
083     * long as its resolution is not requested; whereas pass two and
084     * pass three are performed during the resolution process.
085     * Only four constraints to be checked are explicitly stated by
086     * The Java Virtual Machine Specification, 2nd edition:
087     * <UL>
088     *  <LI>The first four bytes must contain the right magic number (0xCAFEBABE).
089     *  <LI>All recognized attributes must be of the proper length.
090     *  <LI>The class file must not be truncated or have extra bytes at the end.
091     *  <LI>The constant pool must not contain any superficially unrecognizable information.
092     * </UL>
093     * A more in-depth documentation of what pass one should do was written by
094     * <A HREF=mailto:pwfong@cs.sfu.ca>Philip W. L. Fong</A>:
095     * <UL>
096     *  <LI> the file should not be truncated.
097     *  <LI> the file should not have extra bytes at the end.
098     *  <LI> all variable-length structures should be well-formatted:
099     *  <UL>
100     *   <LI> there should only be constant_pool_count-1 many entries in the constant pool.
101     *   <LI> all constant pool entries should have size the same as indicated by their type tag.
102     *   <LI> there are exactly interfaces_count many entries in the interfaces array of the class file.
103     *   <LI> there are exactly fields_count many entries in the fields array of the class file.
104     *   <LI> there are exactly methods_count many entries in the methods array of the class file.
105     *   <LI> there are exactly attributes_count many entries in the attributes array of the class file,
106     *        fields, methods, and code attribute.
107     *   <LI> there should be exactly attribute_length many bytes in each attribute.
108     *        Inconsistency between attribute_length and the actually size of the attribute content should be uncovered.
109     *        For example, in an Exceptions attribute, the actual number of exceptions as required by the number_of_exceptions field
110     *        might yeild an attribute size that doesn't match the attribute_length. Such an anomaly should be detected.
111     *   <LI> all attributes should have proper length. In particular, under certain context (e.g. while parsing method_info),
112     *        recognizable attributes (e.g. "Code" attribute) should have correct format (e.g. attribute_length is 2).
113     *  </UL>
114     *  <LI> Also, certain constant values are checked for validity:
115     *  <UL>
116     *   <LI> The magic number should be 0xCAFEBABE.
117     *   <LI> The major and minor version numbers are valid.
118     *   <LI> All the constant pool type tags are recognizable.
119     *   <LI> All undocumented access flags are masked off before use. Strictly speaking, this is not really a check.
120     *   <LI> The field this_class should point to a string that represents a legal non-array class name,
121     *        and this name should be the same as the class file being loaded.
122     *   <LI> the field super_class should point to a string that represents a legal non-array class name.
123     *   <LI> Because some of the above checks require cross referencing the constant pool entries,
124     *        guards are set up to make sure that the referenced entries are of the right type and the indices
125     *        are within the legal range (0 &lt; index &lt; constant_pool_count).
126     *  </UL>
127     *  <LI> Extra checks done in pass 1:
128     *  <UL>
129     *   <LI> the constant values of static fields should have the same type as the fields.
130     *   <LI> the number of words in a parameter list does not exceed 255 and locals_max.
131     *   <LI> the name and signature of fields and methods are verified to be of legal format.
132     *  </UL>
133     * </UL>
134     * (From the Paper <A HREF="http://www.cs.sfu.ca/people/GradStudents/pwfong/personal/JVM/pass1/">
135     * The Mysterious Pass One, first draft, September 2, 1997</A>.)
136     *
137     * <P>However, most of this is done by parsing a class file or generating a class file into BCEL's internal data structure.
138     * <B>Therefore, all that is really done here is look up the class file from BCEL's repository.</B>
139     * This is also motivated by the fact that some omitted things
140     * (like the check for extra bytes at the end of the class file) are handy when actually using BCEL to repair a class file
141     * (otherwise you would not be able to load it into BCEL).</P>
142     *
143     * @see org.apache.bcel.Repository
144     * @see org.apache.bcel.Const#JVM_CLASSFILE_MAGIC
145     */
146    @Override
147    public VerificationResult do_verify() {
148        JavaClass jc;
149        try{
150            jc = getJavaClass();    //loads in the class file if not already done.
151
152            if (jc != null) {
153                /* If we find more constraints to check, we should do this in an own method. */
154                if (! myOwner.getClassName().equals(jc.getClassName())) {
155                    // This should maybe caught by BCEL: In case of renamed .class files we get wrong
156                    // JavaClass objects here.
157                    throw new LoadingException("Wrong name: the internal name of the .class file '"+jc.getClassName()+
158                        "' does not match the file's name '"+myOwner.getClassName()+"'.");
159                }
160            }
161
162        }
163        catch(final LoadingException e) {
164            return new VerificationResult(VerificationResult.VERIFIED_REJECTED, e.getMessage());
165        }
166        catch(final ClassFormatException e) {
167            return new VerificationResult(VerificationResult.VERIFIED_REJECTED, e.getMessage());
168        }
169        catch(final RuntimeException e) {
170            // BCEL does not catch every possible RuntimeException; e.g. if
171            // a constant pool index is referenced that does not exist.
172            return new VerificationResult(VerificationResult.VERIFIED_REJECTED, "Parsing via BCEL did not succeed. "+
173                e.getClass().getName()+" occured:\n"+Utility.getStackTrace(e));
174        }
175
176        if (jc != null) {
177            return VerificationResult.VR_OK;
178        }
179        //TODO: Maybe change Repository's behaviour to throw a LoadingException instead of just returning "null"
180        //      if a class file cannot be found or in another way be looked up.
181        return new VerificationResult(VerificationResult.VERIFIED_REJECTED, "Repository.lookup() failed. FILE NOT FOUND?");
182    }
183
184    /**
185     * Currently this returns an empty array of String.
186     * One could parse the error messages of BCEL
187     * (written to java.lang.System.err) when loading
188     * a class file such as detecting unknown attributes
189     * or trailing garbage at the end of a class file.
190     * However, Markus Dahm does not like the idea so this
191     * method is currently useless and therefore marked as
192     * <B>TODO</B>.
193     */
194    @Override
195    public String[] getMessages() {
196        // This method is only here to override the javadoc-comment.
197        return super.getMessages();
198    }
199
200}