mprotect errno 22 iOS - ios

Question

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

Answer 1

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