linux-kernel - Re: [PATCH] mm: Fix mmap_assert_locked() in follow

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20240711142218.d7a6cec31366044cbb96a312@linux-foundation.org>
Date: Thu, 11 Jul 2024 14:22:18 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Pei Li <peili.dev@...il.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 skhan@...uxfoundation.org, syzkaller-bugs@...glegroups.com,
 linux-kernel-mentees@...ts.linuxfoundation.org,
 syzbot+35a4414f6e247f515443@...kaller.appspotmail.com, David Hildenbrand
 <david@...hat.com>
Subject: Re: [PATCH] mm: Fix mmap_assert_locked() in follow_pte()

On Wed, 10 Jul 2024 22:13:17 -0700 Pei Li <peili.dev@...il.com> wrote:

> This patch fixes this warning by acquiring read lock before entering
> untrack_pfn() while write lock is not held.
> 
> syzbot has tested the proposed patch and the reproducer did not
> trigger any issue.
> 

Thanks.

> ---
> Syzbot reported the following warning in follow_pte():
> 
> WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 rwsem_assert_held include/linux/rwsem.h:195 [inline]
> WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 mmap_assert_locked include/linux/mmap_lock.h:65 [inline]
> WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 follow_pte+0x414/0x4c0 mm/memory.c:5980
> 
> This is because we are assuming that mm->mmap_lock should be held when
> entering follow_pte(). This is added in commit c5541ba378e3 (mm:
> follow_pte() improvements).
> 
> However, in the following call stack, we are not acquring the lock:
>  follow_phys arch/x86/mm/pat/memtype.c:957 [inline]
>  get_pat_info+0xf2/0x510 arch/x86/mm/pat/memtype.c:991
>  untrack_pfn+0xf7/0x4d0 arch/x86/mm/pat/memtype.c:1104
>  unmap_single_vma+0x1bd/0x2b0 mm/memory.c:1819
>  zap_page_range_single+0x326/0x560 mm/memory.c:1920
> 
> In zap_page_range_single(), we passed mm_wr_locked as false, as we do
> not expect write lock to be held.
> In the special case where vma->vm_flags is set as VM_PFNMAP, we are
> hitting untrack_pfn() which eventually calls into follow_phys.

I included the above (very relevant) info in the changelog.

And I added 

	Fixes: c5541ba378e3 ("mm: follow_pte() improvements")

and queued the patch for 6.10-rc7.  Hopefully David can review it for us.