228 lines
8.0 KiB
Java
228 lines
8.0 KiB
Java
/* ###
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* IP: GHIDRA
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* REVIEWED: YES
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// The Ghidra FindUndefinedFunctionsScript.java script will often incorrectly
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// identify function entry points. This script attempts to find and fix
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// those bad entry points.
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//
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// <b>Issues</b>: Memory bounds checking is hard-coded. It incorrectly identifies random
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// 0x60000000 values that the compiler inserted between some functions
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// as "ori r0,r0,0" instructions that should be added to the head of the
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// functions those values precede. It makes assumptions that wouldn't be helpful in
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// an image that hasn't been mostly disassembled already. I'm sure there are other
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// problems with it. Still, it did a pretty good job of cleaning up after
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// FindUndefinedFunctionsScript.
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//
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//@category CustomerSubmission.Analysis.Repair
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import ghidra.app.script.GhidraScript;
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import ghidra.app.util.PseudoDisassembler;
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import ghidra.app.util.PseudoInstruction;
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import ghidra.program.model.address.Address;
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import ghidra.program.model.lang.*;
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import ghidra.program.model.listing.*;
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import ghidra.program.model.mem.Memory;
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public class FindUndefinedFunctionsFollowUpScript extends GhidraScript {
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@Override
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public void run() throws Exception {
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FunctionIterator funcs = currentProgram.getListing().getFunctions(true);
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Memory mem = currentProgram.getMemory();
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int count = 0;
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while (funcs.hasNext() && !monitor.isCancelled()) {
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Function f = funcs.next();
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Address a = f.getEntryPoint();
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// auto func: starts with "FUN_" and 1st instr is "mfspr r0,LR"
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if (f.getName().startsWith("FUN_") && mem.getInt(a) == 0x7c0802a6) {
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// does func have a few undefined intstructions before it?
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// if so, get frag start address, disassemble frag, remove
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// the defined function, and create a new function at start
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// of frag
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Address fsa = findFrag(a);
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if (fsa != null) {
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disassemble(fsa);
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removeFunction(f);
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String fname = Long.toHexString(fsa.getOffset());
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int i;
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for (i = fname.length(); i < 8; i++)
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fname = "0" + fname;
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fname = "FUN_" + fname;
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createFunction(fsa, fname);
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println("fixed func at 0x" + Long.toHexString(fsa.getOffset()));
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count = count + 1;
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}
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else {
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// does func have a few defined instructions before it
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// that don't include "b" or "blr" and start with an
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// instruction defined as the start of a function?
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// if so then delete function at current address, delete
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// function defined at start of head, and recreate function
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// at start of head (to include what was in function
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// formerly defined at current address)
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Address head = findHead(a);
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if (head != null) {
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removeFunction(f);
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f = getFunctionAt(head);
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String fname = f.getName();
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removeFunction(f);
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createFunction(head, fname);
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println("fixed func at 0x" + Long.toHexString(head.getOffset()));
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count = count + 1;
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}
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}
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}
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}
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println("Fixed " + count + " functions.");
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}
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private Address findFrag(Address a) throws Exception {
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// looking for something like this:
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// 01e328e4 r3 80 00 20 blr // end of prev func
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// 01e328e8 94 ?? 94h
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// 01e328e9 21 ?? 21h
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// 01e328ea ff ?? FFh
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// 01e328eb e0 ?? E0h
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// 01e328ec 2c ?? 2Ch
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// 01e328ed 03 ?? 03h
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// 01e328ee 00 ?? 00h
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// 01e328ef 00 ?? 00h
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// undefined FUN_01e328f0 // <-- Address a
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// 01e328f0 7c 08 02 a6 mfspr r0,LR
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// 01e328f4 39 80 00 31 li r12,0x31
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// ...
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//
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// if there are 1-6 undefined instructions before Address a and
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// a "b" or "blr" instruction before that, then return the address
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// of the dword following the "b" or "blr" instruction -- else
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// return null
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Memory mem = currentProgram.getMemory();
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// save start address before we start scanning backward
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Address sa = a;
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Listing listing = currentProgram.getListing();
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// memory bounds checking is hard-coded -- yes...bad
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// try to find up to 6 undefined instructions before start address
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while (a.getOffset() > 0x1800000 && sa.getOffset() - a.getOffset() < 24 &&
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listing.isUndefined(a.subtract(4), a.subtract(1)) && isInstruction(a.subtract(4))) {
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if (monitor.isCancelled())
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return (null);
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a = a.subtract(4);
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}
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// if the dword we are pointing to isn't undefined, we didn't find frag
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if (!listing.isUndefined(a, a.add(3)))
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return (null);
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// if we didn't find an instruction, then we didn't find a frag
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if (listing.getInstructionAt(a.subtract(4)) == null)
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return (null);
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// if instruction isn't a "b" and isn't a "blr", we didn't find a frag
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int val = mem.getInt(a.subtract(4));
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if ((val & 0xfc000000) != 0x48000000 && val != 0x4e800020)
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return (null);
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// at this point, assume that we found a frag, starting at a
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return (a);
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}
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private boolean isInstruction(Address a) {
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// is undefined dword at specified address a valid instruction?
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PseudoDisassembler pdis = new PseudoDisassembler(currentProgram);
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PseudoInstruction pi = null;
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try {
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pi = pdis.disassemble(a);
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}
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catch (InsufficientBytesException e) {
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println("insufficient bytes at " + Long.toHexString(a.getOffset()));
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return (false);
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}
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catch (UnknownInstructionException e) {
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println("unknown instr at " + Long.toHexString(a.getOffset()));
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}
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catch (UnknownContextException e) {
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println("unknown context at " + Long.toHexString(a.getOffset()));
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}
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if (pi == null)
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return (false);
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return (true);
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}
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private Address findHead(Address a) throws Exception {
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// looking for something like this:
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// undefined FUN_01e328e8
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// 01e328e8 94 21 ff e0 stwu r1,-0x20(r1)
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// 01e328ec 2c 03 00 00 cmpwi r3,0x0
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// undefined FUN_01e328f0 // <-- Address a
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// 01e328f0 7c 08 02 a6 mfspr r0,LR
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// 01e328f4 39 80 00 31 li r12,0x31
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// ...
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// if there are 1-6 defined instructions before Address a, none
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// of them are "b" or "blr", and the first one is defined as the
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// start of a function, then return the address defined as the
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// start of a function -- else return null
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Memory mem = currentProgram.getMemory();
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// save start address before we start scanning backward
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Address sa = a;
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Listing listing = currentProgram.getListing();
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// memory bounds checking is hard-coded -- yes...bad
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// try to find up to 6 instructions before start address that don't
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// include "b" or "blr" and start with instruction defined as start
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// of function
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int val = mem.getInt(a.subtract(4));
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while (a.getOffset() > 0x1800000 && sa.getOffset() - a.getOffset() < 24 &&
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listing.getInstructionAt(a.subtract(4)) != null &&
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((val & 0xfc000000) != 0x48000000 && val != 0x4e800020) &&
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listing.getFunctionAt(a.subtract(4)) == null) {
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if (monitor.isCancelled())
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return (null);
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a = a.subtract(4);
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val = mem.getInt(a.subtract(4));
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}
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// if we found a "b" or "blr", we didn't find a function header
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if ((val & 0xfc000000) == 0x48000000 || val == 0x4e800020)
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return (null);
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// if the instruction before the one we are pointing to isn't
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// a function entry point, we didn't find a function header
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if (listing.getFunctionAt(a.subtract(4)) == null)
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return (null);
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// at this point, assume that we found a function header, starting at a-4
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return (a.subtract(4));
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}
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}
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