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https://github.com/felix-pb/kfd

kfd, short for kernel file descriptor, is a project to read and write kernel memory on Apple devices.
https://github.com/felix-pb/kfd

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kfd, short for kernel file descriptor, is a project to read and write kernel memory on Apple devices.

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README 

        
> Quick disclaimer: I have no intention of adding offsets for other devices and iOS versions.



# kfd



kfd, short for kernel file descriptor, is a project to read and write kernel memory on Apple

devices. It leverages various vulnerabilities that can be exploited to obtain dangling PTEs, which

will be referred to as a PUAF primitive, short for "physical use-after-free". Then, it reallocates

certain kernel objects inside those physical pages and manipulates them directly from user space

through the dangling PTEs in order to achieve a KRKW primitive, short for "kernel read/write". The

exploit code is fully contained in a library, [libkfd](kfd/libkfd.h), but the project also contains

simple executable wrappers for [iOS](kfd/ContentView.swift) and [macOS](macos_kfd.c). The public API

of libkfd is quite small and intuitive:



```c

enum puaf_method {

    puaf_physpuppet,

    puaf_smith,

    puaf_landa,

};



enum kread_method {

    kread_kqueue_workloop_ctl,

    kread_sem_open,

};



enum kwrite_method {

    kwrite_dup,

    kwrite_sem_open,

};



u64 kopen(u64 puaf_pages, u64 puaf_method, u64 kread_method, u64 kwrite_method);

void kread(u64 kfd, u64 kaddr, void* uaddr, u64 size);

void kwrite(u64 kfd, void* uaddr, u64 kaddr, u64 size);

void kclose(u64 kfd);

```



`kopen()` conceptually opens a "kernel file descriptor". It takes the following 4 arguments:



- `puaf_pages`: The target number of physical pages with dangling PTEs.

- `puaf_method`: The method used to obtain the PUAF primitive, with the following options:

    - `puaf_physpuppet`:

        - This method exploits [CVE-2023-23536][1].

        - Fixed in iOS 16.4 and macOS 13.3.

        - Reachable from the App Sandbox but not the WebContent sandbox.

        - $52,500 Apple Security Bounty reward.

    - `puaf_smith`:

        - This method exploits [CVE-2023-32434][2].

        - Fixed in iOS 16.5.1 and macOS 13.4.1.

        - Reachable from the WebContent sandbox and might have been actively exploited.

    - `puaf_landa`:

        - This method exploits [CVE-2023-41974][3].

        - Fixed in iOS 17.0 and macOS 14.0.

        - Reachable from the App Sandbox but not the WebContent sandbox.

        - $70,000 Apple Security Bounty reward.

- `kread_method`: The method used to obtain the initial `kread()` primitive.

- `kwrite_method`: The method used to obtain the initial `kwrite()` primitive.



If the exploit is successful, `kopen()` returns a 64-bit opaque file descriptor. In practice, this

is just a user space pointer to a structure needed by libkfd. However, since that structure should

not be accessed outside of the library, it is returned as an opaque integer. If the exploit is

unsuccessful, the library will print an error message, sleep for 30 seconds, then exit with a status

code of 1. It sleeps for 30 seconds because the kernel might panic on exit for certain PUAF methods

that require some cleanup post-KRKW (e.g. `puaf_smith`).



`kread()` and `kwrite()` are the user space equivalent of `copyout()` and `copyin()`, respectively.

Please note that the options for `kread_method` and `kwrite_method` are described in a separate

[write-up](writeups/exploiting-puafs.md). In addition, the initial primitives granted by those

methods can be used to bootstrap a better KRKW primitive. Finally, `kclose()` simply closes the

kernel file descriptor. They all take the opaque integer returned by `kopen()` as their first

argument.



[1]: https://support.apple.com/en-us/HT213676

[2]: https://support.apple.com/en-us/HT213814

[3]: https://support.apple.com/en-us/HT213938



---



##  How to build and run kfd on an iPhone?



In Xcode, open the root folder of the project and connect your iOS device.



- To build the project, select Product > Build (⌘B).

- To run the project, select Product > Run (⌘R), then click on the "kopen" button in the app.



---



## How to build and run kfd on a Mac?



In a terminal, navigate to the root folder of the project.



Optionally, to increase the global and per-process file descriptor limits, which will improve the

success rate especially on multiple consecutive runs, enter the command `make s` and type in the

sudo password.



- To build the project, enter the command `make b`.

- To run the project, enter the command `make r`.

- To build and run the project at once, enter the command `make br`.



---



## Where to find detailed write-ups for the exploits?



This README presented a high-level overview of the kfd project. Once a PUAF primitive has been

achieved, the rest of the exploit is generic. Therefore, I have hoisted the common part of the

exploits in a dedicated write-up:



- [Exploiting PUAFs](writeups/exploiting-puafs.md)



In addition, I have split the vulnerability-specific part of the exploits used to achieve the PUAF

primitive into distinct write-ups, listed below in chronological order of discovery:



- [PhysPuppet](writeups/physpuppet.md)

- [Smith](writeups/smith.md)

- [Landa](writeups/landa.md)



However, please note that these write-ups have been written for an audience that is already familiar

with the XNU virtual memory system.