| Title | Author | Created | Published | Tags |
| ---------------------------------- | ---------------------------- | ---------------- | ---------------- | ---------------------------- |
| Memory Protection & Paging - mseal | <ul><li>Jon Marien</li></ul> | January 16, 2025 | January 16, 2025 | [[#issessions\|#issessions]] |
---
## Introducing mseal
**Traditional Memory Management:**
- Memory divided into fixed-size blocks called "pages"
- Physical memory split into "frames" of matching size
- Pages swap between RAM and disk storage
- Like a library where books (pages) move between shelves (RAM) and storage (disk)
**Common Memory Issues:**
- Buffer overflows
- Memory corruption
- Unauthorized permission changes
- Page faults when data isn't in RAM
**mseal (2024):**
- New Linux security feature
- "Seals" critical memory sections
- Prevents permission modifications
- Prevents permission changes once sealed
- Works alongside paging system
- Enhances existing page protection
- Maintains paging performance
- Compatible with virtual memory system
```ASCII
Memory Pages
+------------------+
| Normal Page |
+------------------+
| 🔒 SEALED PAGE | ← [❌ Cannot modify permissions]
+------------------+
| Normal Page |
+------------------+
| 🔒 SEALED PAGE | ← [❌ Cannot modify permissions]
+------------------+
| Normal Page |
+------------------+
```
## Script:
Today, I'll be discussing `mseal` and memory management in Linux systems. Let me start with how memory works in modern computers.
Our computers use a system called memory paging. Imagine a library where books (data) are stored either on accessible shelves (RAM) or in a basement archive (disk storage). These books are divided into equal-sized chapters called 'pages.' When you need information, the relevant pages move from storage to RAM. However, this system has historically faced several technical challenges:
- Programs could modify their memory permissions
- Memory corruption and buffer overflows were common
- Page table modifications could be exploited
- Memory management overhead affected performance
The paging system allows computers to handle more data than they have physical RAM by swapping pages in and out as needed. However, this system has traditionally been vulnerable to various security issues. Malicious programs could potentially modify memory permissions, leading to problems like buffer overflows and memory corruption.
This is where `mseal` comes in. Originally introduced in December 2023, `mseal` adds an extra layer of security to this system. Imagine it as a special seal on certain library books that prevents anyone from altering their location or access permissions. Once a memory page is 'sealed,' even if an attacker gains access to the system, they cannot modify the permissions of these protected areas, but it wasn't without its own technical hurdles. The initial implementation faced several criticisms:
- The API design was considered overly complex
- There were concerns about system maintenance becoming more difficult
- Performance impact on high-performance systems was questioned
- Compatibility issues with `libc` operations were identified
- The solution seemed redundant given OpenBSD's existing `mimmutable()` system
- `mimmutable()` is designed for memory sealing in `libc`, and `mseal()` is designed for both Chrome browser (V8 Engine) and `libc`.
Despite these concerns, `mseal` was refined to address these issues. The final implementation provides a robust solution that:
- Works seamlessly with the existing paging system
- Prevents unauthorized permission changes
- Maintains system performance
- Provides critical memory protection
Major applications like Chrome are already implementing `mseal`, demonstrating its practical value in real-world applications. The feature will be included in Linux 6.10, marking a significant advancement in memory protection. This release is set to reach Linux 6.10 in February 2025.
## Sources:
https://dev.to/dumboprogrammer/mseal-in-linux-an-un-hackable-solution-357n
https://blog.trailofbits.com/2024/10/25/a-deep-dive-into-linuxs-new-mseal-syscall/
https://lwn.net/Articles/948129/
https://lwn.net/Articles/954936/
https://youtu.be/FSVnN6-xr9k?si=zU00jEj0oVO5s-1s
https://docs.kernel.org/userspace-api/mseal.html