Cribl AppScope

Introduction

AppScope is an open source instrumentation utility for any application, regardless of programming language, with no code modification required.

AppScope extracts detailed information from applications as they execute, including all file operations, all network operations, and cleartext data from encrypted flows. AppScope enables you to extract all payloads in their entirety. You can capture any console I/O and updates to any log file, and can monitor CPU and memory resource usage in process detail.

Architecture and Operation

AppScope consists of a shared library and an executable. In simple terms, you load the library into the address space of a process. With the library loaded, details are extracted from applications as they execute. The executable provides a command line interface (CLI), which can optionally be used to control which processes are interposed, what data is extracted, and how to view and interact with the results.

The library extracts information as it interposes functions. When an application calls a function, it actually calls a function of the same name in the AppScope library. AppScope extracts details from the function, and the original function call proceeds. This interposition of function calls requires no change to an application: it works with unmodified binaries, and its CPU and memory overhead are minimal.

The library is loaded using a number of mechanisms, depending on the type of executable. A dynamic loader can preload the library (where supported) and AppScope is used to load static executables.

Child processes are created with the library present, if the library was present in the parent. In this manner, a single executable is able to start, daemonize, and create any number of children, all of which include interposed functions.

The executable scope is provided with AppScope. The scope executable provides a rich CLI that allows for exploration of application functionality, and for detailed interaction with the data extracted from the AppScope library. The scope CLI supports an extensive terminal-based dashboard, providing a summary of application details. Views of the data include raw formats exported from the library, as well as formatted output, independent of data type. A history of "scoped" applications is maintained, enabling comparison and capture of full-fidelity application detail.

Requirements

Operating System Support

• RedHat Enterprise Linux or CentOS 6.4 and later
• Ubuntu 16 and later
• Amazon Linux 1 and 2

Resources

• CPU: x84-64 architecture
• Memory: 1GB
• Disk: 20MB

Known Limitations

AppScope does not support the following runtimes:

Open JVM < v.6, Oracle JVM < v.6, Go < v.1.8.

Install and Build

Linux

Check out the code, install build tools, build, and run tests:

git clone https://github.com/criblio/appscope.git
cd appscope
./scope_env.sh build

./scope_env.sh build does everything needed to get a brand new environment up and running. It can also be run on an existing environment to rebuild, and rerun tests. If desired, individual parts of ./scope_env.sh build can be run from the appscope directory:

./install_build_tools.sh
make all
make test

To clean out files that were manually added, or were added by build commands:

git clean -f -d

Run

There are two ways to "scope" an application (i.e., to enable AppScope to extract details from an application). You can use the scope executable, or you can use the dynamic loader's preload capability.

Using scope

The scope executable provides a simple way of "scoping" an application:

scope your_command params

Where "your_command" is any executable and "params" are any parameters needed for the executable.

Using scope in this manner causes your_command to be loaded, as well as loading the AppScope library. The default configuration for scope is to emit all data to the local file system. The path for the data store is configurable. For details, display scope help using the -h or --help command line option:

scope -h

Here is a simple example of invoking the scope executable:

scope bash

This will cause the bash shell to be executed with the AppScope library. All subsequent commands executed from the shell will emit detailed data describing the behavior of the application.

Dynamic Loader

The kernel runs the dynamic loader when an executable is started. The loader determines which executable to load, resolves dependencies, allocates memory, loads code, performs all required link operations, and starts the application. When resolving dependencies, the loader can be configured to load a specific library in addition to the library dependencies associated with the executable. Loading of an additional library is configured by setting the environment variable LD_PRELOAD.

Examples:

LD_PRELOAD=./libscope.so curl https://cribl.io

This will configure the loader to load and run curl, while loading the additional library libscope.so. The result is that AppScope will emit details from the execution of curl. The specific data emitted, the format of the data, the transport for that data are all configurable. Reference the help menu with the libscope.so library:

libscope.so all

From a bash shell prompt:

export LD_PRELOAD=./libscope.so

This will set the LD_PRELOAD environment variable for all commands that execute in the current shell. The result is that all commands executed from the shell will cause libscope.so to be loaded and details of those applications emitted.

The scope Executable

scope provides a rich set of features for exploring data from applications that have been "scoped". scope supports several distinct modes:

• Run an application
• Explore events from "scoped" applications
• Explore metrics from "scoped" applications
• Manage history and the accumulated data set

Developer Notes

• The top-level Makefile checks to see what platform you are on, and then includes the specific Makefile for that platform from the OS-specific directory.

• The run script will determine which platform you are using, and will set environment variables accordingly.