linux-kernel - Re: [syzbot] [mm?] WARNING in __page_table_check_ptes

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Date: Mon, 22 Apr 2024 17:10:15 +0200
From: David Hildenbrand <david@...hat.com>
To: Peter Xu <peterx@...hat.com>
Cc: syzbot <syzbot+d8426b591c36b21c750e@...kaller.appspotmail.com>,
 akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 pasha.tatashin@...een.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] WARNING in __page_table_check_ptes_set

>> commit f369b07c861435bd812a9d14493f71b34132ed6f
>> Author: Peter Xu <peterx@...hat.com>
>> 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