ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 112 insertions, 0 deletions

diff --git a/Documentation/security/secrets/coco.rst b/Documentation/security/secrets/coco.rst
new file mode 100644
index 000000000..a1210db8e
--- /dev/null
+++ b/Documentation/security/secrets/coco.rst
@@ -0,0 +1,103 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==============================
+Confidential Computing secrets
+==============================
+
+This document describes how Confidential Computing secret injection is handled
+from the firmware to the operating system, in the EFI driver and the efi_secret
+kernel module.
+
+
+Introduction
+============
+
+Confidential Computing (coco) hardware such as AMD SEV (Secure Encrypted
+Virtualization) allows guest owners to inject secrets into the VMs
+memory without the host/hypervisor being able to read them.  In SEV,
+secret injection is performed early in the VM launch process, before the
+guest starts running.
+
+The efi_secret kernel module allows userspace applications to access these
+secrets via securityfs.
+
+
+Secret data flow
+================
+
+The guest firmware may reserve a designated memory area for secret injection,
+and publish its location (base GPA and length) in the EFI configuration table
+under a ``LINUX_EFI_COCO_SECRET_AREA_GUID`` entry
+(``adf956ad-e98c-484c-ae11-b51c7d336447``).  This memory area should be marked
+by the firmware as ``EFI_RESERVED_TYPE``, and therefore the kernel should not
+be use it for its own purposes.
+
+During the VM's launch, the virtual machine manager may inject a secret to that
+area.  In AMD SEV and SEV-ES this is performed using the
+``KVM_SEV_LAUNCH_SECRET`` command (see [sev]_).  The structure of the injected
+Guest Owner secret data should be a GUIDed table of secret values; the binary
+format is described in ``drivers/virt/coco/efi_secret/efi_secret.c`` under
+"Structure of the EFI secret area".
+
+On kernel start, the kernel's EFI driver saves the location of the secret area
+(taken from the EFI configuration table) in the ``efi.coco_secret`` field.
+Later it checks if the secret area is populated: it maps the area and checks
+whether its content begins with ``EFI_SECRET_TABLE_HEADER_GUID``
+(``1e74f542-71dd-4d66-963e-ef4287ff173b``).  If the secret area is populated,
+the EFI driver will autoload the efi_secret kernel module, which exposes the
+secrets to userspace applications via securityfs.  The details of the
+efi_secret filesystem interface are in [secrets-coco-abi]_.
+
+
+Application usage example
+=========================
+
+Consider a guest performing computations on encrypted files.  The Guest Owner
+provides the decryption key (= secret) using the secret injection mechanism.
+The guest application reads the secret from the efi_secret filesystem and
+proceeds to decrypt the files into memory and then performs the needed
+computations on the content.
+
+In this example, the host can't read the files from the disk image
+because they are encrypted.  Host can't read the decryption key because
+it is passed using the secret injection mechanism (= secure channel).
+Host can't read the decrypted content from memory because it's a
+confidential (memory-encrypted) guest.
+
+Here is a simple example for usage of the efi_secret module in a guest
+to which an EFI secret area with 4 secrets was injected during launch::
+
+	# ls -la /sys/kernel/security/secrets/coco
+	total 0
+	drwxr-xr-x 2 root root 0 Jun 28 11:54 .
+	drwxr-xr-x 3 root root 0 Jun 28 11:54 ..
+	-r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
+	-r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
+	-r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
+	-r--r----- 1 root root 0 Jun 28 11:54 e6f5a162-d67f-4750-a67c-5d065f2a9910
+
+	# hd /sys/kernel/security/secrets/coco/e6f5a162-d67f-4750-a67c-5d065f2a9910
+	00000000  74 68 65 73 65 2d 61 72  65 2d 74 68 65 2d 6b 61  |these-are-the-ka|
+	00000010  74 61 2d 73 65 63 72 65  74 73 00 01 02 03 04 05  |ta-secrets......|
+	00000020  06 07                                             |..|
+	00000022
+
+	# rm /sys/kernel/security/secrets/coco/e6f5a162-d67f-4750-a67c-5d065f2a9910
+
+	# ls -la /sys/kernel/security/secrets/coco
+	total 0
+	drwxr-xr-x 2 root root 0 Jun 28 11:55 .
+	drwxr-xr-x 3 root root 0 Jun 28 11:54 ..
+	-r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
+	-r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
+	-r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
+
+
+References
+==========
+
+See [sev-api-spec]_ for more info regarding SEV ``LAUNCH_SECRET`` operation.
+
+.. [sev] Documentation/virt/kvm/x86/amd-memory-encryption.rst
+.. [secrets-coco-abi] Documentation/ABI/testing/securityfs-secrets-coco
+.. [sev-api-spec] https://www.amd.com/system/files/TechDocs/55766_SEV-KM_API_Specification.pdf
diff --git a/Documentation/security/secrets/index.rst b/Documentation/security/secrets/index.rst
new file mode 100644
index 000000000..ced34e9c4
--- /dev/null
+++ b/Documentation/security/secrets/index.rst
@@ -0,0 +1,9 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================
+Secrets documentation
+=====================
+
+.. toctree::
+
+   coco