linux-kernel - Re: usbdev_mmap causes type confusion in page_table

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Date:   Mon, 8 May 2023 16:21:57 -0700
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Ruihan Li <lrh2000@....edu.cn>,
        syzbot+fcf1a817ceb50935ce99@...kaller.appspotmail.com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: usbdev_mmap causes type confusion in page_table_check

> 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