Re: [syzbot] [mm?] WARNING in __page_table_check_ptes_set

From: David Hildenbrand
Date: Mon Apr 22 2024 - 11:10:28 EST


commit f369b07c861435bd812a9d14493f71b34132ed6f
Author: Peter Xu <peterx@xxxxxxxxxx>
Date: Thu Aug 11 16:13:40 2022 -0400

mm/uffd: reset write protection when unregister with wp-mode


close should behave just like unregister.


Simplified+readable reproducer:

#define _GNU_SOURCE

#include <stdint.h>
#include <fcntl.h>
#include <sys/syscall.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <linux/userfaultfd.h>
#include <unistd.h>

int main(void)
{
void *src = mmap(0, 4096, PROT_READ, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
void *dst = mmap(0, 4096, PROT_READ, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
struct uffdio_register uffdio_register = {};
struct uffdio_copy uffdio_copy = {};
struct uffdio_api uffdio_api = {};
int uffd;

uffd = syscall(SYS_userfaultfd, O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY);
uffdio_api.api = UFFD_API;
ioctl(uffd, UFFDIO_API, &uffdio_api);

uffdio_register.range.start = (uintptr_t)dst;
uffdio_register.range.len = 4096;
uffdio_register.mode = UFFDIO_REGISTER_MODE_WP;
ioctl(uffd, UFFDIO_REGISTER, &uffdio_register);

uffdio_copy.dst = (uintptr_t)dst;
uffdio_copy.src = (uintptr_t)src;
uffdio_copy.len = 4096;
uffdio_copy.mode = UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP;
ioctl(uffd, UFFDIO_COPY, &uffdio_copy);

close(uffd);

mprotect(dst, 4096, PROT_READ|PROT_WRITE);
return 0;
}

Thanks, I'll post a patch.

PS: next time feel free to try "strace ./reproducer", it'll do the
translations and I found it handy to work with syzbot.

Cool, was not aware that it would do that amount of translation!

--
Cheers,

David / dhildenb