> 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.