Mprotect

Description

mprotect - set protection on a region of memory

Syntax

#include <sys/mman.h>
int mprotect(void *addr, size_t len, int prot);

Parameters

addr

mprotect() changes protection for the calling process's memory page(s) containing any part of the address range in the interval [addr, addr+len-1].

addr must be aligned to a page boundary.

If the calling process tries to access memory in a manner that violates the protection, then the kernel generates a SIGSEGV signal for the process.

len

length

prot

is either PROT_NONE or a bitwise-or of the other values in the following list:

Code	Description
PROT_NONE	The memory cannot be accessed at all.
PROT_READ	The memory can be read.
PROT_WRITE	The memory can be modified.
PROT_EXEC	The memory can be executed.

Return value

On success, mprotect() returns zero. On error, -1 is returned, and errno is set appropriately.

Errors

Code	Decription
EACCES	The memory cannot be given the specified access. This can happen, for example, if you mmap(2) a file to which you have read-only access, then ask mprotect() to mark it PROT_WRITE.
EINVAL	addr is not a valid pointer, or not a multiple of the system page size.
ENOMEM	Internal kernel structures could not be allocated.
ENOMEM	Addresses in the range [addr, addr+len-1] are invalid for the address space of the process, or specify one or more pages that are not mapped. (Before kernel 2.4.19, the error EFAULT was incorrectly produced for these cases.)
ENOMEM	PROT_WRITE would result in three mappings: two read/write mappings at each end and a read-only mapping in the middle.)

Example

LOAD:080485A8                 mov     eax, [esp+18h]
LOAD:080485AC                 and     eax, 0FFFFF000h
LOAD:080485B1                 mov     dword ptr [esp+8], 5 ; prot
LOAD:080485B9                 mov     dword ptr [esp+4], 186h ; len
LOAD:080485C1                 mov     [esp], eax      ; addr
LOAD:080485C4                 call    mprotect
LOAD:080485C9                 mov     [esp+1Ch], eax
LOAD:080485CD                 cmp     dword ptr [esp+1Ch], 0
LOAD:080485D2                 jns     short loc_80485DB
LOAD:080485D4                 mov     eax, 1
LOAD:080485D9                 jmp     short locret_80485E6