Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230515130958.32471-1-lrh2000@pku.edu.cn> <20230515130958.32471-4-lrh2000@pku.edu.cn>
In-Reply-To: <20230515130958.32471-4-lrh2000@pku.edu.cn>
From:   Pasha Tatashin <pasha.tatashin@soleen.com>
Date:   Mon, 15 May 2023 12:36:00 -0400
Message-ID: <CA+CK2bAWg0JejRjzn4e2K7+PgGPE3rXP0qjFwuKOEC-PNPrEPg@mail.gmail.com>
Subject: Re: [PATCH v2 3/4] mm: page_table_check: Make it dependent on EXCLUSIVE_SYSTEM_RAM
To:     Ruihan Li <lrh2000@pku.edu.cn>
Cc:     linux-mm@kvack.org, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org, David Hildenbrand <david@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Hellwig <hch@infradead.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, May 15, 2023 at 9:10=E2=80=AFAM Ruihan Li <lrh2000@pku.edu.cn> wrot=
e:
>
> Without EXCLUSIVE_SYSTEM_RAM, users are allowed to map arbitrary
> physical memory regions into the userspace via /dev/mem. At the same
> time, pages may change their properties (e.g., from anonymous pages to
> named pages) while they are still being mapped in the userspace, leading
> to "corruption" detected by the page table check.
>
> To avoid these false positives, this patch makes PAGE_TABLE_CHECK
> depends on EXCLUSIVE_SYSTEM_RAM. This dependency is understandable
> because PAGE_TABLE_CHECK is a hardening technique but /dev/mem without
> STRICT_DEVMEM (i.e., !EXCLUSIVE_SYSTEM_RAM) is itself a security
> problem.
>
> Even with EXCLUSIVE_SYSTEM_RAM, I/O pages may be still allowed to be
> mapped via /dev/mem. However, these pages are always considered as named
> pages, so they won't break the logic used in the page table check.
>
> Cc: <stable@vger.kernel.org> # 5.17
> Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>

Acked-by: Pasha Tatashin <pasha.tatashin@soleen.com>

Thank you,
Pasha