Changing the right on the text section to make it writeable

chg_mprotect.c

#define  _GNU_SOURCE
#include <unistd.h>
#include <dlfcn.h>
#include <sys/mman.h>
#include <link.h>
#include <errno.h>

/*
 - info: pointer to a dl_phdr_info {
       ElfW(Addr)        dlpi_addr;  // Base address of object
       const char       *dlpi_name;  // (Null-terminated) name of object
       const ElfW(Phdr) *dlpi_phdr;  // Pointer to array of ELF program headers for this object
       ElfW(Half)        dlpi_phnum; // # of items in dlpi_phdr
    }
 - size: size of the  dl_phdr_info
 - data: whatever data sent to dl_iterate_phdr

 With:
 typedef struct {
    Elf32_Word  p_type;    /: Segment type
    Elf32_Off   p_offset;  // Segment file offset
    Elf32_Addr  p_vaddr;   // Segment virtual address
    Elf32_Addr  p_paddr;   // Segment physical address
    Elf32_Word  p_filesz;  // Segment size in file
    Elf32_Word  p_memsz;   // Segment size in memory
    Elf32_Word  p_flags;   // Segment flags
    Elf32_Word  p_align;   // Segment alignment
} Elf32_Phdr;
 */
static int do_write_protect_text(struct dl_phdr_info *info, size_t size, void *data)

{
    const int protect = (data) ? PROT_READ | PROT_EXEC : PROT_READ | PROT_WRITE | PROT_EXEC;
    size_t    page;
    size_t    i;

    page = sysconf(_SC_PAGESIZE);

    if (size < sizeof (struct dl_phdr_info))
        return ENOTSUP;

    /* Ignore libraries. */
    if (info->dlpi_name && info->dlpi_name[0] != '\0')
        return 0;

    /* Loop over each header. */
    for (i = 0; i < (size_t)info->dlpi_phnum; i++)
        if ((info->dlpi_phdr[i].p_flags & PF_X)) {
            size_t ptr = (size_t)info->dlpi_phdr[i].p_vaddr;
            size_t len = (size_t)info->dlpi_phdr[i].p_memsz;

            /* Start at the beginning of the relevant page, */
            if (ptr % page) {
                len += ptr % page;
                ptr -= ptr % page;
            }

            /* and use full pages. */
            if (len % page)
                len += page - (len % page);

            /* Change protections. Ignore unmapped sections. */
            if (mprotect((void *)ptr, len, protect))
                if (errno != ENOMEM)
                    return errno;
        }

    return 0;
}

int write_protect_text(int protect)
{
    int result;

    result = dl_iterate_phdr(do_write_protect_text, (void *)(long)protect);

    if (result)
        errno = result;
    return result;
}