diff: kernel CONFIG_RKP

The difference you're seeing in the kernel source for your Samsung Tab S9 with the addition of:

#ifdef CONFIG_RKP
#include <linux/rkp.h>
#endif

likely relates to Samsung's specific kernel hardening mechanisms. Here's what's happening:

1. RKP (Real-time Kernel Protection): Samsung includes additional security features like RKP in their devices, which are not part of the standard Android GKI (Generic Kernel Image) or mainline Linux kernel branches. RKP is part of Samsung's Knox security suite and is a custom kernel-level protection mechanism designed to defend against kernel compromises in real-time. It helps to protect the integrity of the kernel by monitoring its behavior and preventing malicious activities.

2. Samsung-Specific Kernel Modifications: While the GKI is a standard initiative by Google to maintain a common kernel for Android devices, manufacturers like Samsung often add their own custom patches to support device-specific hardware or enhance security, which can include additional kernel protection mechanisms like RKP. These patches are not present in the GKI kernel sources because they are proprietary to Samsung and may involve specific configurations for their hardware.

3. Device-Specific Security Requirements: Samsung's security and performance requirements for their devices, especially high-end models like the Tab S9, often lead to additional hardening measures. Since RKP is part of their security architecture, it would be implemented through conditional compilation (#ifdef CONFIG_RKP) to ensure it's included only when the necessary configuration (CONFIG_RKP) is enabled during kernel compilation.

In short, this addition is a Samsung-specific kernel modification, part of their Knox security framework, and is absent from the GKI branches because GKI is designed to be more generic and doesn't include proprietary security features from individual manufacturers.