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From:   Pasha Tatashin <pasha.tatashin@soleen.com>
Date:   Mon, 8 May 2023 16:21:57 -0700
Message-ID: <CA+CK2bD=bv1vPGZaNcxDy-uUFj2ZAKkdPmAtJaweXhgTe91oEw@mail.gmail.com>
Subject: Re: usbdev_mmap causes type confusion in page_table_check
To:     David Hildenbrand <david@redhat.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Ruihan Li <lrh2000@pku.edu.cn>,
        syzbot+fcf1a817ceb50935ce99@syzkaller.appspotmail.com,
        akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, gregkh@linuxfoundation.org,
        linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com
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> For normal Kernel-MM operations, vm_normal_page() should be used to
> get "struct page" based on vma+addr+pte combination, but
> page_table_check does not use vma for its operation in order to
> strengthen the verification of no invalid page sharing. But, even
> vm_normal_page() can cause access to the "struct page" for VM_PFNMAP
> if pfn_valid(pfn) is true. So, vm_normal_page() can return a struct
> page for a user mapped slab page.

Only for !ARCH_HAS_PTE_SPECIAL case, otherwise NULL is returned.

Pasha