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Date:   Thu, 24 Sep 2020 19:34:28 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Mike Rapoport <rppt@kernel.org>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christopher Lameter <cl@linux.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        David Hildenbrand <david@redhat.com>,
        Elena Reshetova <elena.reshetova@intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Idan Yaniv <idan.yaniv@ibm.com>,
        Ingo Molnar <mingo@redhat.com>,
        James Bottomley <jejb@linux.ibm.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@infradead.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
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        x86@kernel.org
Subject: Re: [PATCH v6 0/6] mm: introduce memfd_secret system call to create
 "secret" memory areas
Message-Id: <20200924193428.6642e0cc3436bb67ddf8024a@linux-foundation.org>
In-Reply-To: <20200924132904.1391-1-rppt@kernel.org>
References: <20200924132904.1391-1-rppt@kernel.org>
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On Thu, 24 Sep 2020 16:28:58 +0300 Mike Rapoport <rppt@kernel.org> wrote:

> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> Hi,
> 
> This is an implementation of "secret" mappings backed by a file descriptor. 
> I've dropped the boot time reservation patch for now as it is not strictly
> required for the basic usage and can be easily added later either with or
> without CMA.
> 
> ...
> 
> The file descriptor backing secret memory mappings is created using a
> dedicated memfd_secret system call The desired protection mode for the
> memory is configured using flags parameter of the system call. The mmap()
> of the file descriptor created with memfd_secret() will create a "secret"
> memory mapping. The pages in that mapping will be marked as not present in
> the direct map and will have desired protection bits set in the user page
> table. For instance, current implementation allows uncached mappings.
> 
> Although normally Linux userspace mappings are protected from other users, 
> such secret mappings are useful for environments where a hostile tenant is
> trying to trick the kernel into giving them access to other tenants
> mappings.
> 
> Additionally, the secret mappings may be used as a mean to protect guest
> memory in a virtual machine host.
> 
> For demonstration of secret memory usage we've created a userspace library
> [1] that does two things: the first is act as a preloader for openssl to

I can find no [1].

I'm not a fan of the enumerated footnote thing.  Why not inline the url
right here so readers don't need to jump around?