Скачать или смотреть How to Determine the Memory Address Range of Linux-Kernel Objects

Discover how to accurately find the memory address range of Linux kernel functions, particularly from `verifier.c`, by using specific compilation settings and tools.
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Understanding Memory Address Ranges in Linux Kernel

When working with the Linux kernel, especially when inspecting specific components like those in kernel/bpf/verifier.c, it’s essential to know where these functions are loaded in memory. This knowledge can significantly aid in debugging and development tasks. However, extracting this information is not always straightforward, particularly for non-static functions, which are listed in /proc/kallsyms. This post will guide you through the steps necessary to determine the memory address range of these kernel objects effectively.

The Problem: Locating Function Addresses

The core issue you might encounter is wanting to find the memory addresses of all functions defined in a specific C file within the kernel, while ensuring that Kernel Address Space Layout Randomization (KASLR) is managed appropriately. Here's a breakdown of the main points of confusion or challenges faced:

Static vs. Non-static Functions: Only non-static functions are listed in the /proc/kallsyms file.

KASLR: If KASLR is enabled, the addresses of functions can change with each boot, complicating the derivation of consistent memory locations.

Sequential Layout: When KASLR is off, it’s believed that these functions are laid out sequentially within the kernel space.

The Solution: Steps to Determine Memory Address Range

To locate the memory address of functions from kernel/bpf/verifier.c, you can follow these organized steps:

Step 1: Compile the Kernel with Debug Information

To retrieve comprehensive information about function addresses, you need to compile the kernel with debug symbols. Specifically, set the following option in the kernel configuration:

[[See Video to Reveal this Text or Code Snippet]]

This will ensure that the object files generated during compilation include debugging information, which is crucial for identifying function locations accurately.

Step 2: Disable KASLR

Next, you need to make sure KASLR is turned off. This can typically be done by configuring the kernel with the option nokalsr or ensuring that KASLR is set to be disabled during the compile time. This ensures that your functions will have consistent addresses across reboots, simplifying your task.

Step 3: Inspect the vmlinux Binary

Once you've compiled the kernel with the correct options, the next step is to analyze the compiled binary. You can use the readelf tool to extract symbol information from the vmlinux file. Execute the following command in your terminal:

[[See Video to Reveal this Text or Code Snippet]]

This command will provide you with a detailed list of all the symbols (including functions) in the vmlinux binary, along with their respective address ranges.

Step 4: Locate Your Functions

To find the specific functions from verifier.c, you can filter the output of readelf to focus on the relevant entries. Look for the lines corresponding to your target functions, and note their memory addresses.

Conclusion

Locating memory addresses for kernel functions is crucial for developers and maintainers working with the Linux kernel. By compiling the kernel with the debug_info option, disabling KASLR, and using readelf to inspect the vmlinux binary, you can successfully determine the address ranges of your desired functions. The above steps not only simplify this process but also equip you with essential tools to further explore and debug the Linux kernel.

With this understanding, you now have the means to analyze and inspect the kernel's memory more effectively, paving the way for deeper insights into its inner workings.