[PATCH, RFC 57/62] x86/mktme: Overview of Multi-Key Total Memory Encryption

[Kirill A. Shutemov]

From: Alison Schofield <alison.schofield@xxxxxxxxx>

Provide an overview of MKTME on Intel Platforms.

Signed-off-by: Alison Schofield <alison.schofield@xxxxxxxxx>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 Documentation/x86/mktme/index.rst          |  8 +++
 Documentation/x86/mktme/mktme_overview.rst | 57 ++++++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 Documentation/x86/mktme/index.rst
 create mode 100644 Documentation/x86/mktme/mktme_overview.rst

diff --git a/Documentation/x86/mktme/index.rst b/Documentation/x86/mktme/index.rst
new file mode 100644
index 000000000000..1614b52dd3e9
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+++ b/Documentation/x86/mktme/index.rst
@@ -0,0 +1,8 @@
+
+=========================================
+Multi-Key Total Memory Encryption (MKTME)
+=========================================
+
+.. toctree::
+
+   mktme_overview
diff --git a/Documentation/x86/mktme/mktme_overview.rst b/Documentation/x86/mktme/mktme_overview.rst
new file mode 100644
index 000000000000..59c023965554
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+Overview
+=========
+Multi-Key Total Memory Encryption (MKTME)[1] is a technology that
+allows transparent memory encryption in upcoming Intel platforms.
+It uses a new instruction (PCONFIG) for key setup and selects a
+key for individual pages by repurposing physical address bits in
+the page tables.
+
+Support for MKTME is added to the existing kernel keyring subsystem
+and via a new mprotect_encrypt() system call that can be used by
+applications to encrypt anonymous memory with keys obtained from
+the keyring.
+
+This architecture supports encrypting both normal, volatile DRAM
+and persistent memory.  However, persistent memory support is
+not included in the Linux kernel implementation at this time.
+(We anticipate adding that support next.)
+
+Hardware Background
+===================
+
+MKTME is built on top of an existing single-key technology called
+TME.  TME encrypts all system memory using a single key generated
+by the CPU on every boot of the system. TME provides mitigation
+against physical attacks, such as physically removing a DIMM or
+watching memory bus traffic.
+
+MKTME enables the use of multiple encryption keys[2], allowing
+selection of the encryption key per-page using the page tables.
+Encryption keys are programmed into each memory controller and
+the same set of keys is available to all entities on the system
+with access to that memory (all cores, DMA engines, etc...).
+
+MKTME inherits many of the mitigations against hardware attacks
+from TME.  Like TME, MKTME does not mitigate vulnerable or
+malicious operating systems or virtual machine managers.  MKTME
+offers additional mitigations when compared to TME.
+
+TME and MKTME use the AES encryption algorithm in the AES-XTS
+mode.  This mode, typically used for block-based storage devices,
+takes the physical address of the data into account when
+encrypting each block.  This ensures that the effective key is
+different for each block of memory. Moving encrypted content
+across physical address results in garbage on read, mitigating
+block-relocation attacks.  This property is the reason many of
+the discussed attacks require control of a shared physical page
+to be handed from the victim to the attacker.
+
+--
+1. https://software.intel.com/sites/default/files/managed/a5/16/Multi-Key-Total-Memory-Encryption-Spec.pdf
+2. The MKTME architecture supports up to 16 bits of KeyIDs, so a
+   maximum of 65535 keys on top of the âTME keyâ at KeyID-0.  The
+   first implementation is expected to support 5 bits, making 63
+   keys available to applications.  However, this is not guaranteed.
+   The number of available keys could be reduced if, for instance,
+   additional physical address space is desired over additional
+   KeyIDs.
-- 
2.20.1