Debugging ARM code snippets in IDA Pro 5. QEMU emulator – Hex Blog. Introduction. IDA Pro 5. This section of FreeVBCode provides free code on the topic of Files and Directories. These free Visual Basic code snippets, examples, and articles are available for. Snippets are minimal stand-alone programs that demonstrate specific techniques or functionality. Often a small example is the easiest way to understand. QEMU emulator. It can be used to debug small code snippets directly from the database. In this tutorial we will show how to dynamically run code that can be difficult to analyze statically. Target. As an example we will use shellcode from the article “Alphanumeric RISC ARM Shellcode” in Phrack 6. It is self- modifying and because of alphanumeric limitation can be quite hard to undestand. So we will use the debugging feature to decode it. The sample code is at the bottom of the article but here it is repeated: 8. AR8. 0AR8. 0AR8. 0AR8. AR8. 0AR8. 0AR8. 0AR8. AR8. 0AR8. 0AR8. 0AR8. AR8. 0AR8. 0AR8. 0AR8. Introduction; Anatomy of a Lua Call; Hello World; Calling Subroutines, Sending Arguments and Receiving Returns; Passing Tables to Lua Functions. This is a collection of PHP snippets that are really useful for PHP developers. If you know any code snippet you may post/share it for others here: Post a Snippet. INSTRUCTIONS: For each of the following snippets of prose, explain why it is bad writing. These all were first reprinted in The New Yorker. WIRED is where tomorrow is realized. When you provide structured data markup for your online content, you make that content eligible to appear in two categories of Google Search features. Keeping It Catholic Scrapbook A World Wide Collection of Inspiring Stories, Snippets and Vignettes on the Web. AR8. 0AR. 8. 0AR8. AR8. 0AR8. 0AR8. 0AR8. AR8. 0AR8. 0AR8. 0AR0. OB0. 0OR0. 0SU0. 0SE9. PSB9. PSR0p. MB8. SBc. ACP. da. DPq. AGYy. PDRea. OPea. FPea. FPea. FPea. FPea. FPea. FPd. 0FU8. R9p. CRPP7. R0. P5. Bc. PFE6. PCBe. PFE. BP3. Bl. P5. RYPFUVP3. RAP5. RWPFUXp. FUx. GRca. FPa. P7. RAP5. BIPFE8p. 4B0. PMRGA5. X9p. WRAAAO8. P4. B. ga. OP0. 00. Qx. Fd. 0i. 8QCa. 12. ATQC6. 1BTQC0. 11. OBQCA1. 69. OCQCa. Copy this text to a new text file, remove all line breaks (i. Then load it into IDA. Loading binary files into IDAIDA displays the following dialog when it doesn’t recognize the file format (as in this case): Since we know that the code is for ARM processor, choose ARM in the “Processor type” dropdown and click Set. The following dialog appears: When you analyze a real firmware dumped from address 0, these settings are good. However, since our shellcode is not address- dependent, we can choose any address. For example, enter 0x. ROM start address” and “Loading address” fields. IDA doesn’t know anything about this file so it didn’t create any code. Press C to start disassembly. Configuring QEMUBefore starting debug session, we need to set up automatic running of QEMU. Download a recent version of QEMU with ARM support (e. Change “set QEMUFLAGS” if you’re using an older version. In IDA, go to Debug- Debugger options. Choose Versatile or Integrator board. The command line and Initial SP fields will be filled in. Memory map will be filled from the config file too. You can edit it by clicking the “Memory map” button, or from the Debugger- Manual memory regions menu item. Now on every start of debugging session QEMU will be started automatically. Executing the code. By default, initial execution point is the entry point of the database. If you want to execute some other part of it, there are two ways: Select the code range that you want to execute, or. Rename starting point ENTRY and ending point EXIT (convention similar to Bochs debugger)In our case we do want to start at the entry point so we don’t need to do anything. If you press F9 now, IDA will write the database contents to an ELF file (database. QEMU, passing the ELF file name as the “kernel” parameter. QEMU will load it, and stop at the initial point. Now you can step through the code and inspect what it does. Most of the instructions “just work”, however, there is a syscall at 0x. ROM: 0. 00. 10. 11. SVCMI 0x. 41. 41. Since the QEMU configuration we use is “bare metal”, without any operating system, this syscall won’t be handled. So we need to skip it. Navigate to 0. 10. F4 (Run to cursor). Notice that the code was changed (patched by preceding instructions): (Incidentally, 0x. F0. 00. 2 is sys. Once you’re on BXPL R6 line, IDA will detect the mode switch and add a change point to Thumb code: However, the following, previously existing code will (incorrectly) stay in ARM mode. We need to fix that. Go to 0. 10. 12. C and press U (Undefine). Press Alt- G (Change Segment Register Value) and set value of T to 1. The erroneous CODE3. Go back to 0. 00. C (Make code). Nice Thumb code will appear: In Thumb code, there is another syscall at 0. If you trace or run until it, you can see that R7 becomes 0x. B (sys. Return address will be in LR. Saving results to database. If you want to keep the modified code or data for later analysis, you’ll need to copy it to the database. For that: Edit segment attributes (Alt- S) and make sure that segments with the data you need have the “Loader segment” attribute set. Choose Debugger- Take memory snapshot and answer “Loader segments”. Note: if you answer “All segments”, IDA will try to read the whole RAM segment (usually 1. M) which can take a VERY long time. Now you can stop the debugging and inspect the new data. Note: this will update your database with the new data and discard the old. Repeated execution probably will not be correct. This concludes our short tutorial. You can get an offline PDF version with a slightly more complex example andmore background info here. Please send any comments or questions to support@hex- rays.
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