/** Stack Clash kernel "stack gap" patch tester
 *
 * WTFPLv2 - do whatever the fuck you want with this
 * Dominique Martinet <asmadeus@codewreck.org>
 *
 * gcc -o teststackclash teststackclash.c && ./teststackclash
 */

#include <stdio.h>
#include <sys/mman.h>
#include <alloca.h>
#include <unistd.h>
#include <errno.h>
#include <inttypes.h>

#define MMAP_OFFSET (1024*1024)

int main(int argc, char argv[]) {
	void *stackedge, *stackaddr, *mmapaddr;
	char ispresent;

	printf("Address within stack: %p, looking for stack start edge...\n", &stackedge);

	stackedge = (void*)((uintptr_t)&stackedge & 0xfffffffffffff000);
       	while (mincore(stackedge, 1, &ispresent) == 0)
		stackedge -= 4096;

	if (errno != ENOMEM) {
		printf("unexpected mincore errno: %d\n", errno);
		return -1;
	}

	printf("Stack starts here: %p, doing mmap largely before it (%p)\n", stackedge+4096, stackedge-MMAP_OFFSET);
	errno = 0;


	mmapaddr = mmap(stackedge-MMAP_OFFSET, 4096, PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, 0, 0); 
	if (mmapaddr == MAP_FAILED) {
		printf("mmap failed: %d\n", errno);
		return -1;
	}

	if (mmapaddr != stackedge - MMAP_OFFSET) {
		printf("mmap ok, but didn't respect MAP_FIXED hint: %p\n", mmapaddr);
		return -1;
	}

	printf("mmap ok, allocating within stack until it grows (should crash with that mmap)\n");
	while ((stackaddr = alloca(4096)) > stackedge);


	// ((char*)mmapaddr)[0] = 1; // actually didn't even need to write in map
	printf("Didn't crash, stack gap guard <1MB or didn't care about our map\n");

	return 0;
}