MPROTECT(3P)

🌸 MPROTECT(3P) 🌸

okay bestie, welcome to MPROTECT(3P) from the POSIX Programmer's Manual 💖 this is the page that tells you how to change what you're allowed to do with a chunk of memory you already mapped. permission glow-up. periodt. ✨

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📜 PROLOG 📜

okay so first things first, real talk:

• This manual page is part of the POSIX Programmer's Manual. 🎀
• The Linux implementation of this interface may differ — so go consult the corresponding Linux manual page for the deets on Linux behavior, okay? 🙈
• Also possible: the interface may not be implemented on Linux at all. so check before you commit, bestie. 💀

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✨ NAME ✨

mprotect — set protection of memory mapping 💅

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🦋 SYNOPSIS 🦋

#include <sys/mman.h>

int mprotect(void *addr, size_t len, int prot);

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💖 DESCRIPTION 💖

okay so here's the vibe: mprotect() shall change the access protections to be that specified by prot for those whole pages containing any part of the address space of the process starting at address addr and continuing for len bytes. 👑

The parameter prot decides whether read, write, execute, or some combination of accesses are permitted to the data being mapped. and the prot argument should be either PROT_NONE or the bitwise-inclusive OR of one or more of PROT_READ, PROT_WRITE, and PROT_EXEC. that's the whole menu, no secret items. 🍓

If an implementation can't support the combination of access types you specified in prot, then the call to mprotect() shall fail. no cap.

An implementation may permit accesses other than those specified by prot — however, no implementation shall permit a write to succeed where PROT_WRITE has not been set, and no implementation shall permit any access where PROT_NONE alone has been set. 🚫 Implementations shall support at least these values of prot:

• PROT_NONE
• PROT_READ
• PROT_WRITE
• the bitwise-inclusive OR of PROT_READ and PROT_WRITE

If PROT_WRITE is specified, the application shall ensure that it has opened the mapped objects in the specified address range with write permission — unless MAP_PRIVATE was specified in the original mapping — and that's true regardless of whether the file descriptors used to map the objects have since been closed. yes, even then. the receipt stands. 🧾

The implementation may require that addr be a multiple of the page size as returned by sysconf(). 📏

🫶 heads up: the behavior of this function is unspecified if the mapping was not established by a call to mmap(). so like... don't.

😭 and when mprotect() fails for reasons other than [EINVAL], the protections on some of the pages in the range [addr,addr+len) may have been changed. so it's giving ✨partial chaos✨. plan accordingly.

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🌈 RETURN VALUE 🌈

Upon successful completion, mprotect() shall return 0 🎉 otherwise, it shall return -1 and set errno to indicate the error. 💀

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🔥 ERRORS 🔥

The mprotect() function shall fail if:

• EACCES — the prot argument specifies a protection that violates the access permission the process has to the underlying memory object. 🙅
• EAGAIN — the prot argument specifies PROT_WRITE over a MAP_PRIVATE mapping and there are insufficient memory resources to reserve for locking the private page. 😮‍💨
• ENOMEM — addresses in the range [addr,addr+len) are invalid for the address space of a process, or specify one or more pages which are not mapped. 👻
• ENOMEM — the prot argument specifies PROT_WRITE on a MAP_PRIVATE mapping, and it would require more space than the system is able to supply for locking the private pages, if required. 💸
• ENOTSUP — the implementation does not support the combination of accesses requested in the prot argument. 🚫

The mprotect() function may fail if:

• EINVAL — the addr argument is not a multiple of the page size as returned by sysconf(). 📐

The following sections are informative. 💫

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🎀 EXAMPLES 🎀

None. (yes queen, nothing here, moving on ✨)

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👑 APPLICATION USAGE 👑

Most implementations require that addr is a multiple of the page size as returned by sysconf(). literally just. do that. 🫶

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💜 RATIONALE 💜

None.

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⭐ FUTURE DIRECTIONS ⭐

None.

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🧚 SEE ALSO 🧚

• mmap()
• sysconf()
• The Base Definitions volume of POSIX.1‐2017, <sys_mman.h>

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💅 COPYRIGHT 💅

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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okay that's the whole page bestie!! 🫶 this iconic lil number came to you from IEEE/The Open Group, dated 2017 — go protect those pages responsibly, and remember: PROT_NONE means NO access, not "a little access". bye!! 💖✨🦋🎀