kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 129 insertions, 0 deletions

diff --git a/Documentation/admin-guide/device-mapper/dm-inlinecrypt.rst b/Documentation/admin-guide/device-mapper/dm-inlinecrypt.rst
new file mode 100644
index 000000000..76b3aae21
--- /dev/null
+++ b/Documentation/admin-guide/device-mapper/dm-inlinecrypt.rst
@@ -0,0 +1,129 @@
+==============
+dm-inlinecrypt
+==============
+
+Device-Mapper's "inlinecrypt" target provides transparent encryption of block devices
+using the inline encryption hardware.
+
+For a more detailed description of inline encryption, see:
+https://docs.kernel.org/block/inline-encryption.html
+
+Parameters::
+
+	      <cipher> <key> <iv_offset> <device path> \
+	      <offset> [<#opt_params> <opt_params>]
+
+<cipher>
+    Encryption cipher type.
+
+    The cipher specifications format is::
+
+       cipher
+
+    Examples::
+
+       aes-xts-plain64
+
+    The cipher type corresponds to the encryption modes supported by
+    inline crypto in the block layer. Currently, only
+    BLK_ENCRYPTION_MODE_AES_256_XTS (i.e. aes-xts-plain64) is supported.
+
+<key>
+    Key used for encryption. It is encoded either as a hexadecimal number
+    or it can be passed as <key_string> prefixed with single colon
+    character (':') for keys residing in kernel keyring service.
+    You can only use key sizes that are valid for the selected cipher.
+    Note that the size in bytes of a valid key must be in bellow range.
+
+        [BLK_CRYPTO_KEY_TYPE_RAW, BLK_CRYPTO_KEY_TYPE_HW_WRAPPED]
+
+<key_string>
+    The kernel keyring key is identified by string in following format:
+    <key_size>:<keyring_type>:<key_description>.
+
+<key_size>
+    The encryption key size in bytes. The kernel key payload size must match
+    the value passed in <key_size>.
+
+<keyring_type>
+    The type of the key inside the kernel keyring. It can be either 'logon',
+    or 'trusted' kernel key type.
+
+<key_description>
+    The kernel keyring key description inlinecrypt target should look for
+    when loading key of <keyring_type>.
+
+<iv_offset>
+    The IV offset is a sector count that is added to the sector number
+    before creating the IV.
+
+<device path>
+    This is the device that is going to be used as backend and contains the
+    encrypted data.  You can specify it as a path like /dev/xxx or a device
+    number <major>:<minor>.
+
+<offset>
+    Starting sector within the device where the encrypted data begins.
+
+<#opt_params>
+    Number of optional parameters. If there are no optional parameters,
+    the optional parameters section can be skipped or #opt_params can be zero.
+    Otherwise #opt_params is the number of following arguments.
+
+    Example of optional parameters section:
+        keytype:raw allow_discards sector_size:4096 iv_large_sectors
+
+<key_type>
+    The type of the key as seen by the block layer, either standard or
+    hardware-wrapped. The string is supplied in the table as <keytype:raw>
+    or <keytype:hw-wrapped>.
+
+allow_discards
+    Block discard requests (a.k.a. TRIM) are passed through the inlinecrypt
+    device. The default is to ignore discard requests.
+
+    WARNING: Assess the specific security risks carefully before enabling this
+    option.  For example, allowing discards on encrypted devices may lead to
+    the leak of information about the ciphertext device (filesystem type,
+    used space etc.) if the discarded blocks can be located easily on the
+    device later.
+
+sector_size:<bytes>
+    Use <bytes> as the encryption unit instead of 512 bytes sectors.
+    This option can be in range 512 - 4096 bytes and must be power of two.
+    Virtual device will announce this size as a minimal IO and logical sector.
+
+iv_large_sectors
+    Use <sector_size>-based sector numbers for IV generation instead of
+    512-byte sectors.
+
+    For dm-inlinecrypt, this flag must be specified when <sector_size>
+    is larger than 512 bytes. The legacy 512-byte-based IV behavior is
+    not supported.
+
+    When specified, if <sector_size> is 4096 bytes, plain64 IV for the
+    second sector will be 1, and <iv_offset> must be a multiple of
+    <sector_size> (in 512-byte units).
+
+Example scripts
+===============
+Currently, dm-inlinecrypt devices must be set up directly using dmsetup.
+There is no userspace support yet to integrate dm-inlinecrypt with LUKS
+or cryptsetup. In particular, cryptsetup currently only supports
+dm-crypt, and cannot be used to create dm-inlinecrypt mappings.
+
+The following examples demonstrate how to create dm-inlinecrypt devices
+using dmsetup
+
+::
+
+	#!/bin/sh
+	# Create a inlinecrypt device using dmsetup
+	dmsetup create inlinecrypt1 --table "0 `blockdev --getsz $1` inlinecrypt aes-xts-plain64 babebabebabebabebabebabebabebabebabebabebabebabebabebabebabebabe 0 0 $1 0 1 keytype:raw"
+
+::
+
+	#!/bin/sh
+	# Create a inlinecrypt device using dmsetup when encryption key is stored in keyring service
+	dmsetup create inlinecrypt2 --table "0 `blockdev --getsz $1` inlinecrypt aes-xts-plain64 :64:logon:fde:dminlinecrypt_test_key 0 0 $1 0 1 keytype:raw"
+