Android Memory Inspection Techniques and Tools
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Virtual Memory
Chapter 4 Virtual Memory Linux processes execute in a virtual environment that makes it appear as if each process had the entire address space of the CPU available to itself. This virtual address space extends from address 0 all the way to the maximum address. On a 32-bit platform, such as IA-32, the maximum address is 232 − 1or0xffffffff. On a 64-bit platform, such as IA-64, this is 264 − 1or0xffffffffffffffff. While it is obviously convenient for a process to be able to access such a huge ad- dress space, there are really three distinct, but equally important, reasons for using virtual memory. 1. Resource virtualization. On a system with virtual memory, a process does not have to concern itself with the details of how much physical memory is available or which physical memory locations are already in use by some other process. In other words, virtual memory takes a limited physical resource (physical memory) and turns it into an infinite, or at least an abundant, resource (virtual memory). 2. Information isolation. Because each process runs in its own address space, it is not possible for one process to read data that belongs to another process. This improves security because it reduces the risk of one process being able to spy on another pro- cess and, e.g., steal a password. 3. Fault isolation. Processes with their own virtual address spaces cannot overwrite each other’s memory. This greatly reduces the risk of a failure in one process trig- gering a failure in another process. That is, when a process crashes, the problem is generally limited to that process alone and does not cause the entire machine to go down. -
The Linux Kernel Module Programming Guide
The Linux Kernel Module Programming Guide Peter Jay Salzman Michael Burian Ori Pomerantz Copyright © 2001 Peter Jay Salzman 2007−05−18 ver 2.6.4 The Linux Kernel Module Programming Guide is a free book; you may reproduce and/or modify it under the terms of the Open Software License, version 1.1. You can obtain a copy of this license at http://opensource.org/licenses/osl.php. This book is distributed in the hope it will be useful, but without any warranty, without even the implied warranty of merchantability or fitness for a particular purpose. The author encourages wide distribution of this book for personal or commercial use, provided the above copyright notice remains intact and the method adheres to the provisions of the Open Software License. In summary, you may copy and distribute this book free of charge or for a profit. No explicit permission is required from the author for reproduction of this book in any medium, physical or electronic. Derivative works and translations of this document must be placed under the Open Software License, and the original copyright notice must remain intact. If you have contributed new material to this book, you must make the material and source code available for your revisions. Please make revisions and updates available directly to the document maintainer, Peter Jay Salzman <[email protected]>. This will allow for the merging of updates and provide consistent revisions to the Linux community. If you publish or distribute this book commercially, donations, royalties, and/or printed copies are greatly appreciated by the author and the Linux Documentation Project (LDP). -
Memory Management and Garbage Collection
Overview Memory Management Stack: Data on stack (local variables on activation records) have lifetime that coincides with the life of a procedure call. Memory for stack data is allocated on entry to procedures ::: ::: and de-allocated on return. Heap: Data on heap have lifetimes that may differ from the life of a procedure call. Memory for heap data is allocated on demand (e.g. malloc, new, etc.) ::: ::: and released Manually: e.g. using free Automatically: e.g. using a garbage collector Compilers Memory Management CSE 304/504 1 / 16 Overview Memory Allocation Heap memory is divided into free and used. Free memory is kept in a data structure, usually a free list. When a new chunk of memory is needed, a chunk from the free list is returned (after marking it as used). When a chunk of memory is freed, it is added to the free list (after marking it as free) Compilers Memory Management CSE 304/504 2 / 16 Overview Fragmentation Free space is said to be fragmented when free chunks are not contiguous. Fragmentation is reduced by: Maintaining different-sized free lists (e.g. free 8-byte cells, free 16-byte cells etc.) and allocating out of the appropriate list. If a small chunk is not available (e.g. no free 8-byte cells), grab a larger chunk (say, a 32-byte chunk), subdivide it (into 4 smaller chunks) and allocate. When a small chunk is freed, check if it can be merged with adjacent areas to make a larger chunk. Compilers Memory Management CSE 304/504 3 / 16 Overview Manual Memory Management Programmer has full control over memory ::: with the responsibility to manage it well Premature free's lead to dangling references Overly conservative free's lead to memory leaks With manual free's it is virtually impossible to ensure that a program is correct and secure. -
The Case for Compressed Caching in Virtual Memory Systems
THE ADVANCED COMPUTING SYSTEMS ASSOCIATION The following paper was originally published in the Proceedings of the USENIX Annual Technical Conference Monterey, California, USA, June 6-11, 1999 The Case for Compressed Caching in Virtual Memory Systems _ Paul R. Wilson, Scott F. Kaplan, and Yannis Smaragdakis aUniversity of Texas at Austin © 1999 by The USENIX Association All Rights Reserved Rights to individual papers remain with the author or the author's employer. Permission is granted for noncommercial reproduction of the work for educational or research purposes. This copyright notice must be included in the reproduced paper. USENIX acknowledges all trademarks herein. For more information about the USENIX Association: Phone: 1 510 528 8649 FAX: 1 510 548 5738 Email: [email protected] WWW: http://www.usenix.org The Case for Compressed Caching in Virtual Memory Systems Paul R. Wilson, Scott F. Kaplan, and Yannis Smaragdakis Dept. of Computer Sciences University of Texas at Austin Austin, Texas 78751-1182 g fwilson|sfkaplan|smaragd @cs.utexas.edu http://www.cs.utexas.edu/users/oops/ Abstract In [Wil90, Wil91b] we proposed compressed caching for virtual memory—storing pages in compressed form Compressed caching uses part of the available RAM to in a main memory compression cache to reduce disk pag- hold pages in compressed form, effectively adding a new ing. Appel also promoted this idea [AL91], and it was level to the virtual memory hierarchy. This level attempts evaluated empirically by Douglis [Dou93] and by Russi- to bridge the huge performance gap between normal (un- novich and Cogswell [RC96]. Unfortunately Douglis’s compressed) RAM and disk. -
Oracle® Linux 7 Release Notes for Oracle Linux 7.2
Oracle® Linux 7 Release Notes for Oracle Linux 7.2 E67200-22 March 2021 Oracle Legal Notices Copyright © 2015, 2021 Oracle and/or its affiliates. This software and related documentation are provided under a license agreement containing restrictions on use and disclosure and are protected by intellectual property laws. Except as expressly permitted in your license agreement or allowed by law, you may not use, copy, reproduce, translate, broadcast, modify, license, transmit, distribute, exhibit, perform, publish, or display any part, in any form, or by any means. Reverse engineering, disassembly, or decompilation of this software, unless required by law for interoperability, is prohibited. The information contained herein is subject to change without notice and is not warranted to be error-free. If you find any errors, please report them to us in writing. If this is software or related documentation that is delivered to the U.S. Government or anyone licensing it on behalf of the U.S. Government, then the following notice is applicable: U.S. GOVERNMENT END USERS: Oracle programs (including any operating system, integrated software, any programs embedded, installed or activated on delivered hardware, and modifications of such programs) and Oracle computer documentation or other Oracle data delivered to or accessed by U.S. Government end users are "commercial computer software" or "commercial computer software documentation" pursuant to the applicable Federal Acquisition Regulation and agency-specific supplemental regulations. As such, the use, reproduction, duplication, release, display, disclosure, modification, preparation of derivative works, and/or adaptation of i) Oracle programs (including any operating system, integrated software, any programs embedded, installed or activated on delivered hardware, and modifications of such programs), ii) Oracle computer documentation and/or iii) other Oracle data, is subject to the rights and limitations specified in the license contained in the applicable contract. -
Memory Protection at Option
Memory Protection at Option Application-Tailored Memory Safety in Safety-Critical Embedded Systems – Speicherschutz nach Wahl Auf die Anwendung zugeschnittene Speichersicherheit in sicherheitskritischen eingebetteten Systemen Der Technischen Fakultät der Universität Erlangen-Nürnberg zur Erlangung des Grades Doktor-Ingenieur vorgelegt von Michael Stilkerich Erlangen — 2012 Als Dissertation genehmigt von der Technischen Fakultät Universität Erlangen-Nürnberg Tag der Einreichung: 09.07.2012 Tag der Promotion: 30.11.2012 Dekan: Prof. Dr.-Ing. Marion Merklein Berichterstatter: Prof. Dr.-Ing. Wolfgang Schröder-Preikschat Prof. Dr. Michael Philippsen Abstract With the increasing capabilities and resources available on microcontrollers, there is a trend in the embedded industry to integrate multiple software functions on a single system to save cost, size, weight, and power. The integration raises new requirements, thereunder the need for spatial isolation, which is commonly established by using a memory protection unit (MPU) that can constrain access to the physical address space to a fixed set of address regions. MPU-based protection is limited in terms of available hardware, flexibility, granularity and ease of use. Software-based memory protection can provide an alternative or complement MPU-based protection, but has found little attention in the embedded domain. In this thesis, I evaluate qualitative and quantitative advantages and limitations of MPU-based memory protection and software-based protection based on a multi-JVM. I developed a framework composed of the AUTOSAR OS-like operating system CiAO and KESO, a Java implementation for deeply embedded systems. The framework allows choosing from no memory protection, MPU-based protection, software-based protection, and a combination of the two. -
Ben Livshits 1 Basic Instrumentation
Runtime monitoring CO444H Ben Livshits 1 Basic Instrumentation • Insert additional code into the program • This code is designed to record important events as they occur at runtime • Some examples • A particular function is being hit or a statement is being hit • This leads to function-level or line-level coverage • Each allocation to measure overall memory allocation 2 Levels of Instrumentation • Native code • Instrument machine code • Tools like LLVM are often used for rewriting • Bytecode • Common for languages such as Java and C# • A variety of tools are available for each bytecode format • JoeQ is in this category as well, although it’s a lot more general • Source code • Common for languages like JavaScript • Often the easiest option – parse the code and add more statements 3 Runtime Code Monitoring •Three major examples of monitoring • Purify/Valgrind • Detecting data races • Detecting memory leaks 4 5 Memory Error Detection Purify • C and C++ are not type-safe • The type system and the runtime fail to enforce type safety • What are some of the examples? • Possible to read and write outside of your intended data structures • Write beyond loop bounds • Or object bounds • Or overwrite the code pointer, etc. 6 Track Each Byte of Memory • Three states for every byte of tracker memory • Unallocated: cannot be read or written • Allocated but not initialized: cannot be read • Allocated and initialized: all operations are allowed 7 Instrumentation for Purify • Check the state of each byte at every access • Binary instrumentation: • Add -
Project Snowflake: Non-Blocking Safe Manual Memory Management in .NET
Project Snowflake: Non-blocking Safe Manual Memory Management in .NET Matthew Parkinson Dimitrios Vytiniotis Kapil Vaswani Manuel Costa Pantazis Deligiannis Microsoft Research Dylan McDermott Aaron Blankstein Jonathan Balkind University of Cambridge Princeton University July 26, 2017 Abstract Garbage collection greatly improves programmer productivity and ensures memory safety. Manual memory management on the other hand often delivers better performance but is typically unsafe and can lead to system crashes or security vulnerabilities. We propose integrating safe manual memory management with garbage collection in the .NET runtime to get the best of both worlds. In our design, programmers can choose between allocating objects in the garbage collected heap or the manual heap. All existing applications run unmodified, and without any performance degradation, using the garbage collected heap. Our programming model for manual memory management is flexible: although objects in the manual heap can have a single owning pointer, we allow deallocation at any program point and concurrent sharing of these objects amongst all the threads in the program. Experimental results from our .NET CoreCLR implementation on real-world applications show substantial performance gains especially in multithreaded scenarios: up to 3x savings in peak working sets and 2x improvements in runtime. 1 Introduction The importance of garbage collection (GC) in modern software cannot be overstated. GC greatly improves programmer productivity because it frees programmers from the burden of thinking about object lifetimes and freeing memory. Even more importantly, GC prevents temporal memory safety errors, i.e., uses of memory after it has been freed, which often lead to security breaches. Modern generational collectors, such as the .NET GC, deliver great throughput through a combination of fast thread-local bump allocation and cheap collection of young objects [63, 18, 61]. -
Memory Leak Or Dangling Pointer
Modern C++ for Computer Vision and Image Processing Igor Bogoslavskyi Outline Using pointers Pointers are polymorphic Pointer “this” Using const with pointers Stack and Heap Memory leaks and dangling pointers Memory leak Dangling pointer RAII 2 Using pointers in real world Using pointers for classes Pointers can point to objects of custom classes: 1 std::vector<int> vector_int; 2 std::vector<int >* vec_ptr = &vector_int; 3 MyClass obj; 4 MyClass* obj_ptr = &obj; Call object functions from pointer with -> 1 MyClass obj; 2 obj.MyFunc(); 3 MyClass* obj_ptr = &obj; 4 obj_ptr->MyFunc(); obj->Func() (*obj).Func() ↔ 4 Pointers are polymorphic Pointers are just like references, but have additional useful properties: Can be reassigned Can point to ‘‘nothing’’ (nullptr) Can be stored in a vector or an array Use pointers for polymorphism 1 Derived derived; 2 Base* ptr = &derived; Example: for implementing strategy store a pointer to the strategy interface and initialize it with nullptr and check if it is set before calling its methods 5 1 #include <iostream > 2 #include <vector > 3 using std::cout; 4 struct AbstractShape { 5 virtual void Print() const = 0; 6 }; 7 struct Square : public AbstractShape { 8 void Print() const override { cout << "Square\n";} 9 }; 10 struct Triangle : public AbstractShape { 11 void Print() const override { cout << "Triangle\n";} 12 }; 13 int main() { 14 std::vector<AbstractShape*> shapes; 15 Square square; 16 Triangle triangle; 17 shapes.push_back(&square); 18 shapes.push_back(&triangle); 19 for (const auto* shape : shapes) { shape->Print(); } 20 return 0; 21 } 6 this pointer Every object of a class or a struct holds a pointer to itself This pointer is called this Allows the objects to: Return a reference to themselves: return *this; Create copies of themselves within a function Explicitly show that a member belongs to the current object: this->x(); 7 Using const with pointers Pointers can point to a const variable: 1 // Cannot change value , can reassign pointer. -
The Xen Port of Kexec / Kdump a Short Introduction and Status Report
The Xen Port of Kexec / Kdump A short introduction and status report Magnus Damm Simon Horman VA Linux Systems Japan K.K. www.valinux.co.jp/en/ Xen Summit, September 2006 Magnus Damm ([email protected]) Kexec / Kdump Xen Summit, September 2006 1 / 17 Outline Introduction to Kexec What is Kexec? Kexec Examples Kexec Overview Introduction to Kdump What is Kdump? Kdump Kernels The Crash Utility Xen Porting Effort Kexec under Xen Kdump under Xen The Dumpread Tool Partial Dumps Current Status Magnus Damm ([email protected]) Kexec / Kdump Xen Summit, September 2006 2 / 17 Introduction to Kexec Outline Introduction to Kexec What is Kexec? Kexec Examples Kexec Overview Introduction to Kdump What is Kdump? Kdump Kernels The Crash Utility Xen Porting Effort Kexec under Xen Kdump under Xen The Dumpread Tool Partial Dumps Current Status Magnus Damm ([email protected]) Kexec / Kdump Xen Summit, September 2006 3 / 17 Kexec allows you to reboot from Linux into any kernel. as long as the new kernel doesn’t depend on the BIOS for setup. Introduction to Kexec What is Kexec? What is Kexec? “kexec is a system call that implements the ability to shutdown your current kernel, and to start another kernel. It is like a reboot but it is indepedent of the system firmware...” Configuration help text in Linux-2.6.17 Magnus Damm ([email protected]) Kexec / Kdump Xen Summit, September 2006 4 / 17 . as long as the new kernel doesn’t depend on the BIOS for setup. Introduction to Kexec What is Kexec? What is Kexec? “kexec is a system call that implements the ability to shutdown your current kernel, and to start another kernel. -
Effective and Efficient Memory Protection Using Dynamic Tainting
1 Effective and Efficient Memory Protection Using Dynamic Tainting Ioannis Doudalis, Student Member, IEEE, James Clause, Member, IEEE, Guru Venkataramani, Member, IEEE, Milos Prvulovic, Senior Member, IEEE, and Alessandro Orso, Member, IEEE, ! Abstract—Programs written in languages allowing direct access to pointer p or a pointer derived from p and 2) if the access memory through pointers often contain memory-related faults, which occurs during the interval when p is valid, (i.e. between the cause non-deterministic failures and security vulnerabilities. We present allocation and deallocation of m). All other accesses to m are a new dynamic tainting technique to detect illegal memory accesses. illegal memory accesses (IMAs), where a pointer is used to When memory is allocated, at runtime, we taint both the memory and the corresponding pointer using the same taint mark. Taint marks access memory outside the bounds of the memory area with are then propagated and checked every time a memory address m which it was originally associated, or outside the time period is accessed through a pointer p; if the associated taint marks differ, during which the pointer is valid. an illegal access is reported. To allow always-on checking using a IMAs are especially relevant for several reasons. First, they low-overhead, hardware-assisted implementation, we make several key are caused by typical programming errors, such as array-out- technical decisions. We use a configurable, low number of reusable taint of-bounds accesses and stale pointer dereferences, and are thus marks instead of a unique mark for each allocated area of memory, reducing the performance overhead without losing the ability to target widespread and common. -
Anatomy of Linux Loadable Kernel Modules a 2.6 Kernel Perspective
Anatomy of Linux loadable kernel modules A 2.6 kernel perspective Skill Level: Intermediate M. Tim Jones ([email protected]) Consultant Engineer Emulex Corp. 16 Jul 2008 Linux® loadable kernel modules, introduced in version 1.2 of the kernel, are one of the most important innovations in the Linux kernel. They provide a kernel that is both scalable and dynamic. Discover the ideas behind loadable modules, and learn how these independent objects dynamically become part of the Linux kernel. The Linux kernel is what's known as a monolithic kernel, which means that the majority of the operating system functionality is called the kernel and runs in a privileged mode. This differs from a micro-kernel, which runs only basic functionality as the kernel (inter-process communication [IPC], scheduling, basic input/output [I/O], memory management) and pushes other functionality outside the privileged space (drivers, network stack, file systems). You'd think that Linux is then a very static kernel, but in fact it's quite the opposite. Linux can be dynamically altered at run time through the use of Linux kernel modules (LKMs). More in Tim's Anatomy of... series on developerWorks • Anatomy of Linux flash file systems • Anatomy of Security-Enhanced Linux (SELinux) • Anatomy of real-time Linux architectures • Anatomy of the Linux SCSI subsystem • Anatomy of the Linux file system • Anatomy of the Linux networking stack Anatomy of Linux loadable kernel modules © Copyright IBM Corporation 1994, 2008. All rights reserved. Page 1 of 11 developerWorks® ibm.com/developerWorks • Anatomy of the Linux kernel • Anatomy of the Linux slab allocator • Anatomy of Linux synchronization methods • All of Tim's Anatomy of..