VM_MAP_PROTECT(9)

💖 VM_MAP_PROTECT 💖

okay so bestie, welcome to vm_map_protect from section 9 of the Kernel Developer's Manual — it's giving kernel internals, it's giving virtual memory, and honestly? we're obsessed 🫶

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✨ NAME ✨

vm_map_protect — apply protection bits to a virtual memory region

like, it goes in and changes the permissions on a chunk of memory, no big deal 💅

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🌸 SYNOPSIS 🌸

#include <sys/param.h>
#include <vm/vm.h>
#include <vm/vm_map.h>

int
vm_map_protect(vm_map_t map, vm_offset_t start, vm_offset_t end,
    vm_prot_t new_prot, boolean_t set_max);

okay so you pull in those three headers — <sys/param.h>, <vm/vm.h>, and <vm/vm_map.h> — and then you call it with a map, a start, an end, a new protection value, and a boolean that decides how spicy you're feeling 🔥

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🦋 DESCRIPTION 🦋

So vm_map_protect() sets the protection bits of the address region bounded by start and end inside the map map, and it sets them to new_prot. Periodt.

But here's the tea ☕ — the value you pass as new_prot may not include any protection bits that aren't already set in max_protection on every single entry within that range. Every. Single. One. No sneaking extra perms past the max, bestie, that's not the vibe 🙈

If set_max is TRUE, then new_prot gets treated as the brand new max_protection setting for each underlying entry. And any protection bits not included in new_prot will get cleared from existing entries. So it's not just a glow-up, it's a full reset of what's allowed. 💀

If set_max is FALSE, only the protection field is affected — the max stays exactly where it was. Chill. Lowkey. 🧚

The range MUST be contiguous, and it MUST NOT contain sub-maps. This is not a suggestion, this is the law, and the function will be very dramatic about it if you try.

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👑 IMPLEMENTATION NOTES 👑

The function acquires a lock on the map for the duration, by calling vm_map_lock(9). So the whole operation is locked down, main character energy, nobody else is touching that map while this is happening 💅

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⭐ RETURN VALUES ⭐

• KERN_SUCCESS — returned if the protection bits could be set successfully. slay ✨
• KERN_INVALID_ARGUMENT — returned if a sub-map entry was encountered in the range. you were told. 😭
• KERN_PROTECTION_FAILURE — returned if the value of new_prot would exceed max_protection for an entry within the range. the ceiling said no. 🚫

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🌈 SEE ALSO 🌈

• vm_map(9)

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🎀 AUTHORS 🎀

This manual page was written by Bruce M Simpson <bms@spc.org>. king behavior, fr fr 👑

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and that's the whole page, bestie 💖 this one's from the Debian crew and it's dated June 20, 2019 — so yeah, it's a classic, and now you know it, and honestly? iykyk 🦋