> For the complete documentation index, see [llms.txt](https://breaking-bits.gitbook.io/breaking-bits/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://breaking-bits.gitbook.io/breaking-bits/exploit-development/linux-kernel-exploit-development/supervisor-mode-access-prevention-smap.md).

# Supervisor Mode Access Prevention (SMAP)

Supervisor Mode Access Prevention is a mitigation [introduced by intel](https://lwn.net/Articles/517475/) to prevent the CPU executing in kernel mode from executing usermode instructions.

There is a SMAP bit in the CR4 control register that dictates whether user-space memory is allowed to be accessed while in a privileged mode. If the bit is set and the processor attempts to access a userspace region of memory, then a page fault will trigger a SMAP violation and result in OOPS.

This means that a ROPChain can't be stored in userspace, or else a SMAP violation will occur. Throughout this exploit series, the chain has been stored in kernel space, so the existing exploit will still work when adding the SMAP protection.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://breaking-bits.gitbook.io/breaking-bits/exploit-development/linux-kernel-exploit-development/supervisor-mode-access-prevention-smap.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.