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Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user
 mappings
To:     Mike Rapoport <rppt@kernel.org>, linux-kernel@vger.kernel.org
Cc:     Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        James Bottomley <jejb@linux.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-api@vger.kernel.org,
        linux-mm@kvack.org, x86@kernel.org,
        Mike Rapoport <rppt@linux.ibm.com>
References: <1572171452-7958-1-git-send-email-rppt@kernel.org>
 <1572171452-7958-2-git-send-email-rppt@kernel.org>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <085ed07e-e646-f7a4-0370-06f33a2a4e4a@redhat.com>
Date:   Tue, 29 Oct 2019 12:02:34 +0100
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On 27.10.19 11:17, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
>=20
> The mappings created with MAP_EXCLUSIVE are visible only in the context o=
f
> the owning process and can be used by applications to store secret
> information that will not be visible not only to other processes but to t=
he
> kernel as well.
>=20
> The pages in these mappings are removed from the kernel direct map and
> marked with PG_user_exclusive flag. When the exclusive area is unmapped,
> the pages are mapped back into the direct map.
>=20

Just a thought, the kernel is still able to indirectly read the contents=20
of these pages by doing a kdump from kexec environment, right?. Also, I=20
wonder what would happen if you map such pages via /dev/mem into another=20
user space application and e.g., use them along with kvm [1].

[1] https://lwn.net/Articles/778240/

--=20

Thanks,

David / dhildenb