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    The following form allows you to view linux man pages.

    Command:

    mprotect

    
    
    

    SYNOPSIS

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

    DESCRIPTION

           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 pro-
           cess.
    
           prot  is  either  PROT_NONE  or a bitwise-or of the other values in the
           following list:
    
           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

           EACCES The  memory cannot be given the specified access.  This can hap-
                  pen, 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.)
    
    
    

    CONFORMING TO

           SVr4,  POSIX.1-2001.   POSIX  says  that  the behavior of mprotect() is
           unspecified if it is applied  to  a  region  of  memory  that  was  not
           obtained via mmap(2).
    
    
    

    NOTES

           On  Linux it is always permissible to call mprotect() on any address in
           a process's address space (except for the kernel  vsyscall  area).   In
           these pages read-only, and then  executes  a  loop  that  walks  upward
           through the allocated region modifying bytes.
    
           An example of what we might see when running the program is the follow-
           ing:
    
               $ ./a.out
               Start of region:        0x804c000
               Got SIGSEGV at address: 0x804e000
    
       Program source
    
           #include <unistd.h>
           #include <signal.h>
           #include <stdio.h>
           #include <malloc.h>
           #include <stdlib.h>
           #include <errno.h>
           #include <sys/mman.h>
    
           #define handle_error(msg) \
               do { perror(msg); exit(EXIT_FAILURE); } while (0)
    
           static char *buffer;
    
           static void
           handler(int sig, siginfo_t *si, void *unused)
           {
               printf("Got SIGSEGV at address: 0x%lx\n",
                       (long) si->si_addr);
               exit(EXIT_FAILURE);
           }
    
           int
           main(int argc, char *argv[])
           {
               char *p;
               int pagesize;
               struct sigaction sa;
    
               sa.sa_flags = SA_SIGINFO;
               sigemptyset(&sa.sa_mask);
               sa.sa_sigaction = handler;
               if (sigaction(SIGSEGV, &sa, NULL) == -1)
                   handle_error("sigaction");
    
               pagesize = sysconf(_SC_PAGE_SIZE);
               if (pagesize == -1)
                   handle_error("sysconf");
    
               /* Allocate a buffer aligned on a page boundary;
                  initial protection is PROT_READ | PROT_WRITE */
    
               printf("Loop completed\n");     /* Should never happen */
               exit(EXIT_SUCCESS);
           }
    
    
    

    SEE ALSO

           mmap(2), sysconf(3)
    
    
    

    Linux 2014-01-05 MPROTECT(2)

    
    
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