[SOLVED] mprotect errno 22 iOS

mprotect errno 22 iOS

I'm developing a jailbroken app on iOS and getting errno 22 when calling

mprotect(p, 1024, PROT_READ | PROT_EXEC)

errno 22 means invalid arguments but I can't figure out whats wrong. I've aligned p to be a multiple of page size, and I've malloced the memory previously before calling mprotect.

Here's my code and sample output

#define PAGESIZE 4096

FILE * pFile;
pFile = fopen ("log.txt","w");

uint32_t code[] = {
    0xe2800001, // add  r0, r0, #1
    0xe12fff1e, // bx   lr
};

fprintf(pFile, "Before Execution\n");

p = (uint32_t *)malloc(1024+PAGESIZE-1);

if (!p) {
    fprintf(pFile, "Couldn't malloc(1024)");
    perror("Couldn't malloc(1024)");
    exit(errno);
}

fprintf(pFile, "Malloced to %p\n", p);

p = (uint32_t *)(((uintptr_t)p + PAGESIZE-1) & ~(PAGESIZE-1));

fprintf(pFile, "Moved pointer to %p\n", p);

fprintf(pFile, "Before Compiling\n");

// copy instructions to function
p[0] = code[0];
p[1] = code[1];

fprintf(pFile, "After Compiling\n");

if (mprotect(p, 1024, PROT_READ | PROT_EXEC)) {
    int err = errno;
    fprintf(pFile, "Couldn't mprotect2: %i\n", errno);
    perror("Couldn't mprotect");
    exit(errno);
}

And output:

Before Execution
Malloced to 0x13611ec00
Moved pointer 0x13611f000
Before Compiling
After Compiling
Couldn't mprotect2: 22

Solution

Fixed this by using posix_memalign(). Turns out I wasn't aligning my pointer to the page size correctly