Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. SPDX-License-Identifier: GPL-2.0
+
+.. _inline_encryption:
+
+=================
+Inline Encryption
+=================
+
+Background
+==========
+
+Inline encryption hardware sits logically between memory and disk, and can
+en/decrypt data as it goes in/out of the disk.  For each I/O request, software
+can control exactly how the inline encryption hardware will en/decrypt the data
+in terms of key, algorithm, data unit size (the granularity of en/decryption),
+and data unit number (a value that determines the initialization vector(s)).
+
+Some inline encryption hardware accepts all encryption parameters including raw
+keys directly in low-level I/O requests.  However, most inline encryption
+hardware instead has a fixed number of "keyslots" and requires that the key,
+algorithm, and data unit size first be programmed into a keyslot.  Each
+low-level I/O request then just contains a keyslot index and data unit number.
+
+Note that inline encryption hardware is very different from traditional crypto
+accelerators, which are supported through the kernel crypto API.  Traditional
+crypto accelerators operate on memory regions, whereas inline encryption
+hardware operates on I/O requests.  Thus, inline encryption hardware needs to be
+managed by the block layer, not the kernel crypto API.
+
+Inline encryption hardware is also very different from "self-encrypting drives",
+such as those based on the TCG Opal or ATA Security standards.  Self-encrypting
+drives don't provide fine-grained control of encryption and provide no way to
+verify the correctness of the resulting ciphertext.  Inline encryption hardware
+provides fine-grained control of encryption, including the choice of key and
+initialization vector for each sector, and can be tested for correctness.
+
+Objective
+=========
+
+We want to support inline encryption in the kernel.  To make testing easier, we
+also want support for falling back to the kernel crypto API when actual inline
+encryption hardware is absent.  We also want inline encryption to work with
+layered devices like device-mapper and loopback (i.e. we want to be able to use
+the inline encryption hardware of the underlying devices if present, or else
+fall back to crypto API en/decryption).
+
+Constraints and notes
+=====================
+
+- We need a way for upper layers (e.g. filesystems) to specify an encryption
+  context to use for en/decrypting a bio, and device drivers (e.g. UFSHCD) need
+  to be able to use that encryption context when they process the request.
+  Encryption contexts also introduce constraints on bio merging; the block layer
+  needs to be aware of these constraints.
+
+- Different inline encryption hardware has different supported algorithms,
+  supported data unit sizes, maximum data unit numbers, etc.  We call these
+  properties the "crypto capabilities".  We need a way for device drivers to
+  advertise crypto capabilities to upper layers in a generic way.
+
+- Inline encryption hardware usually (but not always) requires that keys be
+  programmed into keyslots before being used.  Since programming keyslots may be
+  slow and there may not be very many keyslots, we shouldn't just program the
+  key for every I/O request, but rather keep track of which keys are in the
+  keyslots and reuse an already-programmed keyslot when possible.
+
+- Upper layers typically define a specific end-of-life for crypto keys, e.g.
+  when an encrypted directory is locked or when a crypto mapping is torn down.
+  At these times, keys are wiped from memory.  We must provide a way for upper
+  layers to also evict keys from any keyslots they are present in.
+
+- When possible, device-mapper devices must be able to pass through the inline
+  encryption support of their underlying devices.  However, it doesn't make
+  sense for device-mapper devices to have keyslots themselves.
+
+Basic design
+============
+
+We introduce ``struct blk_crypto_key`` to represent an inline encryption key and
+how it will be used.  This includes the actual bytes of the key; the size of the
+key; the algorithm and data unit size the key will be used with; and the number
+of bytes needed to represent the maximum data unit number the key will be used
+with.
+
+We introduce ``struct bio_crypt_ctx`` to represent an encryption context.  It
+contains a data unit number and a pointer to a blk_crypto_key.  We add pointers
+to a bio_crypt_ctx to ``struct bio`` and ``struct request``; this allows users
+of the block layer (e.g. filesystems) to provide an encryption context when
+creating a bio and have it be passed down the stack for processing by the block
+layer and device drivers.  Note that the encryption context doesn't explicitly
+say whether to encrypt or decrypt, as that is implicit from the direction of the
+bio; WRITE means encrypt, and READ means decrypt.
+
+We also introduce ``struct blk_crypto_profile`` to contain all generic inline
+encryption-related state for a particular inline encryption device.  The
+blk_crypto_profile serves as the way that drivers for inline encryption hardware
+advertise their crypto capabilities and provide certain functions (e.g.,
+functions to program and evict keys) to upper layers.  Each device driver that
+wants to support inline encryption will construct a blk_crypto_profile, then
+associate it with the disk's request_queue.
+
+The blk_crypto_profile also manages the hardware's keyslots, when applicable.
+This happens in the block layer, so that users of the block layer can just
+specify encryption contexts and don't need to know about keyslots at all, nor do
+device drivers need to care about most details of keyslot management.
+
+Specifically, for each keyslot, the block layer (via the blk_crypto_profile)
+keeps track of which blk_crypto_key that keyslot contains (if any), and how many
+in-flight I/O requests are using it.  When the block layer creates a
+``struct request`` for a bio that has an encryption context, it grabs a keyslot
+that already contains the key if possible.  Otherwise it waits for an idle
+keyslot (a keyslot that isn't in-use by any I/O), then programs the key into the
+least-recently-used idle keyslot using the function the device driver provided.
+In both cases, the resulting keyslot is stored in the ``crypt_keyslot`` field of
+the request, where it is then accessible to device drivers and is released after
+the request completes.
+
+``struct request`` also contains a pointer to the original bio_crypt_ctx.
+Requests can be built from multiple bios, and the block layer must take the
+encryption context into account when trying to merge bios and requests.  For two
+bios/requests to be merged, they must have compatible encryption contexts: both
+unencrypted, or both encrypted with the same key and contiguous data unit
+numbers.  Only the encryption context for the first bio in a request is
+retained, since the remaining bios have been verified to be merge-compatible
+with the first bio.
+
+To make it possible for inline encryption to work with request_queue based
+layered devices, when a request is cloned, its encryption context is cloned as
+well.  When the cloned request is submitted, it is then processed as usual; this
+includes getting a keyslot from the clone's target device if needed.
+
+blk-crypto-fallback
+===================
+
+It is desirable for the inline encryption support of upper layers (e.g.
+filesystems) to be testable without real inline encryption hardware, and
+likewise for the block layer's keyslot management logic.  It is also desirable
+to allow upper layers to just always use inline encryption rather than have to
+implement encryption in multiple ways.
+
+Therefore, we also introduce *blk-crypto-fallback*, which is an implementation
+of inline encryption using the kernel crypto API.  blk-crypto-fallback is built
+into the block layer, so it works on any block device without any special setup.
+Essentially, when a bio with an encryption context is submitted to a
+block_device that doesn't support that encryption context, the block layer will
+handle en/decryption of the bio using blk-crypto-fallback.
+
+For encryption, the data cannot be encrypted in-place, as callers usually rely
+on it being unmodified.  Instead, blk-crypto-fallback allocates bounce pages,
+fills a new bio with those bounce pages, encrypts the data into those bounce
+pages, and submits that "bounce" bio.  When the bounce bio completes,
+blk-crypto-fallback completes the original bio.  If the original bio is too
+large, multiple bounce bios may be required; see the code for details.
+
+For decryption, blk-crypto-fallback "wraps" the bio's completion callback
+(``bi_complete``) and private data (``bi_private``) with its own, unsets the
+bio's encryption context, then submits the bio.  If the read completes
+successfully, blk-crypto-fallback restores the bio's original completion
+callback and private data, then decrypts the bio's data in-place using the
+kernel crypto API.  Decryption happens from a workqueue, as it may sleep.
+Afterwards, blk-crypto-fallback completes the bio.
+
+In both cases, the bios that blk-crypto-fallback submits no longer have an
+encryption context.  Therefore, lower layers only see standard unencrypted I/O.
+
+blk-crypto-fallback also defines its own blk_crypto_profile and has its own
+"keyslots"; its keyslots contain ``struct crypto_skcipher`` objects.  The reason
+for this is twofold.  First, it allows the keyslot management logic to be tested
+without actual inline encryption hardware.  Second, similar to actual inline
+encryption hardware, the crypto API doesn't accept keys directly in requests but
+rather requires that keys be set ahead of time, and setting keys can be
+expensive; moreover, allocating a crypto_skcipher can't happen on the I/O path
+at all due to the locks it takes.  Therefore, the concept of keyslots still
+makes sense for blk-crypto-fallback.
+
+Note that regardless of whether real inline encryption hardware or
+blk-crypto-fallback is used, the ciphertext written to disk (and hence the
+on-disk format of data) will be the same (assuming that both the inline
+encryption hardware's implementation and the kernel crypto API's implementation
+of the algorithm being used adhere to spec and function correctly).
+
+blk-crypto-fallback is optional and is controlled by the
+``CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK`` kernel configuration option.
+
+API presented to users of the block layer
+=========================================
+
+``blk_crypto_config_supported()`` allows users to check ahead of time whether
+inline encryption with particular crypto settings will work on a particular
+block_device -- either via hardware or via blk-crypto-fallback.  This function
+takes in a ``struct blk_crypto_config`` which is like blk_crypto_key, but omits
+the actual bytes of the key and instead just contains the algorithm, data unit
+size, etc.  This function can be useful if blk-crypto-fallback is disabled.
+
+``blk_crypto_init_key()`` allows users to initialize a blk_crypto_key.
+
+Users must call ``blk_crypto_start_using_key()`` before actually starting to use
+a blk_crypto_key on a block_device (even if ``blk_crypto_config_supported()``
+was called earlier).  This is needed to initialize blk-crypto-fallback if it
+will be needed.  This must not be called from the data path, as this may have to
+allocate resources, which may deadlock in that case.
+
+Next, to attach an encryption context to a bio, users should call
+``bio_crypt_set_ctx()``.  This function allocates a bio_crypt_ctx and attaches
+it to a bio, given the blk_crypto_key and the data unit number that will be used
+for en/decryption.  Users don't need to worry about freeing the bio_crypt_ctx
+later, as that happens automatically when the bio is freed or reset.
+
+Finally, when done using inline encryption with a blk_crypto_key on a
+block_device, users must call ``blk_crypto_evict_key()``.  This ensures that
+the key is evicted from all keyslots it may be programmed into and unlinked from
+any kernel data structures it may be linked into.
+
+In summary, for users of the block layer, the lifecycle of a blk_crypto_key is
+as follows:
+
+1. ``blk_crypto_config_supported()`` (optional)
+2. ``blk_crypto_init_key()``
+3. ``blk_crypto_start_using_key()``
+4. ``bio_crypt_set_ctx()`` (potentially many times)
+5. ``blk_crypto_evict_key()`` (after all I/O has completed)
+6. Zeroize the blk_crypto_key (this has no dedicated function)
+
+If a blk_crypto_key is being used on multiple block_devices, then
+``blk_crypto_config_supported()`` (if used), ``blk_crypto_start_using_key()``,
+and ``blk_crypto_evict_key()`` must be called on each block_device.
+
+API presented to device drivers
+===============================
+
+A device driver that wants to support inline encryption must set up a
+blk_crypto_profile in the request_queue of its device.  To do this, it first
+must call ``blk_crypto_profile_init()`` (or its resource-managed variant
+``devm_blk_crypto_profile_init()``), providing the number of keyslots.
+
+Next, it must advertise its crypto capabilities by setting fields in the
+blk_crypto_profile, e.g. ``modes_supported`` and ``max_dun_bytes_supported``.
+
+It then must set function pointers in the ``ll_ops`` field of the
+blk_crypto_profile to tell upper layers how to control the inline encryption
+hardware, e.g. how to program and evict keyslots.  Most drivers will need to
+implement ``keyslot_program`` and ``keyslot_evict``.  For details, see the
+comments for ``struct blk_crypto_ll_ops``.
+
+Once the driver registers a blk_crypto_profile with a request_queue, I/O
+requests the driver receives via that queue may have an encryption context.  All
+encryption contexts will be compatible with the crypto capabilities declared in
+the blk_crypto_profile, so drivers don't need to worry about handling
+unsupported requests.  Also, if a nonzero number of keyslots was declared in the
+blk_crypto_profile, then all I/O requests that have an encryption context will
+also have a keyslot which was already programmed with the appropriate key.
+
+If the driver implements runtime suspend and its blk_crypto_ll_ops don't work
+while the device is runtime-suspended, then the driver must also set the ``dev``
+field of the blk_crypto_profile to point to the ``struct device`` that will be
+resumed before any of the low-level operations are called.
+
+If there are situations where the inline encryption hardware loses the contents
+of its keyslots, e.g. device resets, the driver must handle reprogramming the
+keyslots.  To do this, the driver may call ``blk_crypto_reprogram_all_keys()``.
+
+Finally, if the driver used ``blk_crypto_profile_init()`` instead of
+``devm_blk_crypto_profile_init()``, then it is responsible for calling
+``blk_crypto_profile_destroy()`` when the crypto profile is no longer needed.
+
+Layered Devices
+===============
+
+Request queue based layered devices like dm-rq that wish to support inline
+encryption need to create their own blk_crypto_profile for their request_queue,
+and expose whatever functionality they choose. When a layered device wants to
+pass a clone of that request to another request_queue, blk-crypto will
+initialize and prepare the clone as necessary.
+
+Interaction between inline encryption and blk integrity
+=======================================================
+
+At the time of this patch, there is no real hardware that supports both these
+features. However, these features do interact with each other, and it's not
+completely trivial to make them both work together properly. In particular,
+when a WRITE bio wants to use inline encryption on a device that supports both
+features, the bio will have an encryption context specified, after which
+its integrity information is calculated (using the plaintext data, since
+the encryption will happen while data is being written), and the data and
+integrity info is sent to the device. Obviously, the integrity info must be
+verified before the data is encrypted. After the data is encrypted, the device
+must not store the integrity info that it received with the plaintext data
+since that might reveal information about the plaintext data. As such, it must
+re-generate the integrity info from the ciphertext data and store that on disk
+instead. Another issue with storing the integrity info of the plaintext data is
+that it changes the on disk format depending on whether hardware inline
+encryption support is present or the kernel crypto API fallback is used (since
+if the fallback is used, the device will receive the integrity info of the
+ciphertext, not that of the plaintext).
+
+Because there isn't any real hardware yet, it seems prudent to assume that
+hardware implementations might not implement both features together correctly,
+and disallow the combination for now. Whenever a device supports integrity, the
+kernel will pretend that the device does not support hardware inline encryption
+(by setting the blk_crypto_profile in the request_queue of the device to NULL).
+When the crypto API fallback is enabled, this means that all bios with and
+encryption context will use the fallback, and IO will complete as usual.  When
+the fallback is disabled, a bio with an encryption context will be failed.