[RFC 17/19] fwctl: add detailed IOCTL API specifications

Sasha Levin
2025-06-14T13:49:16Z

Add kernel API specifications to the fwctl driver using the IOCTL
specification framework. This provides detailed documentation and
enables runtime validation of the fwctl IOCTL interface.

Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/fwctl/main.c | 295 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 293 insertions(+), 2 deletions(-)

diff --git a/drivers/fwctl/main.c b/drivers/fwctl/main.c
index bc6378506296c..fc85d54ecb6a0 100644
--- a/drivers/fwctl/main.c
+++ b/drivers/fwctl/main.c
@@ -10,6 +10,8 @@
#include <linux/module.h>
#include <linux/sizes.h>
#include <linux/slab.h>
+#include <linux/ioctl_api_spec.h>
+#include <linux/kernel_api_spec.h>

#include <uapi/fwctl/fwctl.h>

@@ -261,13 +263,291 @@ static int fwctl_fops_release(struct inode *inode, struct file *filp)
return 0;
}

-static const struct file_operations fwctl_fops = {
+/* Use KAPI_DEFINE_FOPS for automatic validation wrapping */
+KAPI_DEFINE_FOPS(fwctl_fops,
.owner = THIS_MODULE,
.open = fwctl_fops_open,
.release = fwctl_fops_release,
.unlocked_ioctl = fwctl_fops_ioctl,
+);
+
+/* IOCTL API Specifications */
+
+static const struct kapi_ioctl_spec fwctl_info_spec = {
+ .cmd = FWCTL_INFO,
+ .cmd_name = "FWCTL_INFO",
+ .input_size = sizeof(struct fwctl_info),
+ .output_size = sizeof(struct fwctl_info),
+ .file_ops_name = "fwctl_fops",
+ .api_spec = {
+ .name = "fwctl_info",
+ KAPI_DESCRIPTION("Query device information and capabilities")
+ KAPI_LONG_DESC("Returns basic information about the fwctl instance, "
+ "including the device type and driver-specific data. "
+ "The driver-specific data format depends on the device type.")
+ KAPI_CONTEXT(KAPI_CTX_PROCESS | KAPI_CTX_SLEEPABLE)
+
+ /* Parameters */
+ KAPI_IOCTL_PARAM_SIZE
+ KAPI_IOCTL_PARAM_FLAGS
+
+ KAPI_PARAM(2, "out_device_type", "__u32", "Device type from enum fwctl_device_type")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_OUT)
+ .type = KAPI_TYPE_UINT,
+ .constraint_type = KAPI_CONSTRAINT_ENUM,
+ .enum_values = (const s64[]){FWCTL_DEVICE_TYPE_ERROR,
+ FWCTL_DEVICE_TYPE_MLX5,
+ FWCTL_DEVICE_TYPE_CXL,
+ FWCTL_DEVICE_TYPE_PDS},
+ .enum_count = 4,
+ KAPI_PARAM_END
+
+ KAPI_PARAM(3, "device_data_len", "__u32", "Length of device data buffer")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_INOUT)
+ .type = KAPI_TYPE_UINT,
+ .constraint_type = KAPI_CONSTRAINT_RANGE,
+ .min_value = 0,
+ .max_value = SZ_1M, /* Reasonable limit for device info */
+ KAPI_PARAM_END
+
+ KAPI_IOCTL_PARAM_USER_OUT_BUF(4, "out_device_data",
+ "Driver-specific device data", 3)
+
+ /* Return value */
+ KAPI_RETURN("int", "0 on success, negative errno on failure")
+ .type = KAPI_TYPE_INT,
+ .check_type = KAPI_RETURN_ERROR_CHECK,
+ .error_values = (const s64[]){-EFAULT, -EOPNOTSUPP, -ENODEV},
+ .error_count = 3,
+ KAPI_RETURN_END
+
+ /* Errors */
+ KAPI_ERROR(0, -EFAULT, "EFAULT", "Failed to copy data to/from user space",
+ "Check that provided pointers are valid user space addresses")
+ KAPI_ERROR(1, -EOPNOTSUPP, "EOPNOTSUPP", "Invalid flags provided",
+ "Currently flags must be 0")
+ KAPI_ERROR(2, -ENODEV, "ENODEV", "Device has been hot-unplugged",
+ "The underlying device is no longer available")
+
+ .error_count = 3,
+ .param_count = 5,
+ .since_version = "6.13",
+
+ /* Structure specifications */
+ KAPI_STRUCT_SPEC(0, fwctl_info, "Device information query structure")
+ KAPI_STRUCT_SIZE(sizeof(struct fwctl_info), __alignof__(struct fwctl_info))
+ KAPI_STRUCT_FIELD_COUNT(4)
+
+ KAPI_STRUCT_FIELD(0, "size", KAPI_TYPE_UINT, "__u32",
+ "Structure size for versioning")
+ KAPI_FIELD_OFFSET(offsetof(struct fwctl_info, size))
+ KAPI_FIELD_SIZE(sizeof(__u32))
+ KAPI_STRUCT_FIELD_END
+
+ KAPI_STRUCT_FIELD(1, "flags", KAPI_TYPE_UINT, "__u32",
+ "Must be 0, reserved for future use")
+ KAPI_FIELD_OFFSET(offsetof(struct fwctl_info, flags))
+ KAPI_FIELD_SIZE(sizeof(__u32))
+ KAPI_FIELD_CONSTRAINT_RANGE(0, 0)
+ KAPI_STRUCT_FIELD_END
+
+ KAPI_STRUCT_FIELD(2, "out_device_type", KAPI_TYPE_UINT, "__u32",
+ "Device type identifier")
+ KAPI_FIELD_OFFSET(offsetof(struct fwctl_info, out_device_type))
+ KAPI_FIELD_SIZE(sizeof(__u32))
+ KAPI_STRUCT_FIELD_END
+
+ KAPI_STRUCT_FIELD(3, "device_data_len", KAPI_TYPE_UINT, "__u32",
+ "Length of device-specific data")
+ KAPI_FIELD_OFFSET(offsetof(struct fwctl_info, device_data_len))
+ KAPI_FIELD_SIZE(sizeof(__u32))
+ KAPI_STRUCT_FIELD_END
+ KAPI_STRUCT_SPEC_END
+
+ KAPI_STRUCT_SPEC_COUNT(1)
+
+ /* Side effects */
+ KAPI_SIDE_EFFECT(0, KAPI_EFFECT_NONE,
+ "none",
+ "Read-only operation with no side effects")
+ KAPI_SIDE_EFFECT_END
+
+ KAPI_SIDE_EFFECT_COUNT(1)
+
+ /* State transitions */
+ KAPI_STATE_TRANS_COUNT(0) /* No state transitions for query operation */
+ },
};

+static const struct kapi_ioctl_spec fwctl_rpc_spec = {
+ .cmd = FWCTL_RPC,
+ .cmd_name = "FWCTL_RPC",
+ .input_size = sizeof(struct fwctl_rpc),
+ .output_size = sizeof(struct fwctl_rpc),
+ .file_ops_name = "fwctl_fops",
+ .api_spec = {
+ .name = "fwctl_rpc",
+ KAPI_DESCRIPTION("Execute a Remote Procedure Call to device firmware")
+ KAPI_LONG_DESC("Delivers an RPC to the device firmware and returns the response. "
+ "The RPC format is device-specific and determined by out_device_type "
+ "from FWCTL_INFO. Different scopes have different permission requirements.")
+ KAPI_CONTEXT(KAPI_CTX_PROCESS | KAPI_CTX_SLEEPABLE)
+
+ /* Parameters */
+ KAPI_IOCTL_PARAM_SIZE
+
+ KAPI_PARAM(1, "scope", "__u32", "Access scope from enum fwctl_rpc_scope")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_IN)
+ .type = KAPI_TYPE_UINT,
+ .constraint_type = KAPI_CONSTRAINT_ENUM,
+ .enum_values = (const s64[]){FWCTL_RPC_CONFIGURATION,
+ FWCTL_RPC_DEBUG_READ_ONLY,
+ FWCTL_RPC_DEBUG_WRITE,
+ FWCTL_RPC_DEBUG_WRITE_FULL},
+ .enum_count = 4,
+ .constraints = "FWCTL_RPC_DEBUG_WRITE_FULL requires CAP_SYS_RAWIO",
+ KAPI_PARAM_END
+
+ KAPI_PARAM(2, "in_len", "__u32", "Length of input buffer")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_IN)
+ .type = KAPI_TYPE_UINT,
+ .constraint_type = KAPI_CONSTRAINT_RANGE,
+ .min_value = 0,
+ .max_value = MAX_RPC_LEN,
+ KAPI_PARAM_END
+
+ KAPI_PARAM(3, "out_len", "__u32", "Length of output buffer")
+ KAPI_PARAM_FLAGS(KAPI_PARAM_INOUT)
+ .type = KAPI_TYPE_UINT,
+ .constraint_type = KAPI_CONSTRAINT_RANGE,
+ .min_value = 0,
+ .max_value = MAX_RPC_LEN,
+ KAPI_PARAM_END
+
+ KAPI_IOCTL_PARAM_USER_BUF(4, "in", "RPC request in device-specific format", 2)
+ KAPI_IOCTL_PARAM_USER_OUT_BUF(5, "out", "RPC response in device-specific format", 3)
+
+ /* Return value */
+ KAPI_RETURN("int", "0 on success, negative errno on failure")
+ .type = KAPI_TYPE_INT,
+ .check_type = KAPI_RETURN_ERROR_CHECK,
+ .error_values = (const s64[]){-EMSGSIZE, -EOPNOTSUPP, -EPERM,
+ -ENOMEM, -EFAULT, -ENODEV},
+ .error_count = 6,
+ KAPI_RETURN_END
+
+ /* Errors */
+ KAPI_ERROR(0, -EMSGSIZE, "EMSGSIZE", "RPC message too large",
+ "in_len or out_len exceeds MAX_RPC_LEN (2MB)")
+ KAPI_ERROR(1, -EOPNOTSUPP, "EOPNOTSUPP", "Invalid scope value",
+ "scope must be one of the defined fwctl_rpc_scope values")
+ KAPI_ERROR(2, -EPERM, "EPERM", "Insufficient permissions",
+ "FWCTL_RPC_DEBUG_WRITE_FULL requires CAP_SYS_RAWIO")
+ KAPI_ERROR(3, -ENOMEM, "ENOMEM", "Memory allocation failed",
+ "Unable to allocate buffers for RPC")
+ KAPI_ERROR(4, -EFAULT, "EFAULT", "Failed to copy data to/from user space",
+ "Check that provided pointers are valid user space addresses")
+ KAPI_ERROR(5, -ENODEV, "ENODEV", "Device has been hot-unplugged",
+ "The underlying device is no longer available")
+
+ .error_count = 6,
+ .param_count = 6,
+ .since_version = "6.13",
+ .notes = "FWCTL_RPC_DEBUG_WRITE and FWCTL_RPC_DEBUG_WRITE_FULL will "
+ "taint the kernel with TAINT_FWCTL on first use",
+
+ /* Structure specifications */
+ KAPI_STRUCT_SPEC(0, fwctl_rpc, "RPC request/response structure")
+ KAPI_STRUCT_SIZE(sizeof(struct fwctl_rpc), __alignof__(struct fwctl_rpc))
+ KAPI_STRUCT_FIELD_COUNT(6)
+
+ KAPI_STRUCT_FIELD(0, "size", KAPI_TYPE_UINT, "__u32",
+ "Structure size for versioning")
+ KAPI_FIELD_OFFSET(offsetof(struct fwctl_rpc, size))
+ KAPI_FIELD_SIZE(sizeof(__u32))
+ KAPI_STRUCT_FIELD_END
+
+ KAPI_STRUCT_FIELD(1, "scope", KAPI_TYPE_UINT, "__u32",
+ "Access scope level")
+ KAPI_FIELD_OFFSET(offsetof(struct fwctl_rpc, scope))
+ KAPI_FIELD_SIZE(sizeof(__u32))
+ KAPI_FIELD_CONSTRAINT_ENUM((const s64[]){FWCTL_RPC_CONFIGURATION,
+ FWCTL_RPC_DEBUG_READ_ONLY,
+ FWCTL_RPC_DEBUG_WRITE,
+ FWCTL_RPC_DEBUG_WRITE_FULL}, 4)
+ KAPI_STRUCT_FIELD_END
+
+ KAPI_STRUCT_FIELD(2, "in_len", KAPI_TYPE_UINT, "__u32",
+ "Input data length")
+ KAPI_FIELD_OFFSET(offsetof(struct fwctl_rpc, in_len))
+ KAPI_FIELD_SIZE(sizeof(__u32))
+ KAPI_STRUCT_FIELD_END
+
+ KAPI_STRUCT_FIELD(3, "out_len", KAPI_TYPE_UINT, "__u32",
+ "Output buffer length")
+ KAPI_FIELD_OFFSET(offsetof(struct fwctl_rpc, out_len))
+ KAPI_FIELD_SIZE(sizeof(__u32))
+ KAPI_STRUCT_FIELD_END
+
+ KAPI_STRUCT_FIELD(4, "in", KAPI_TYPE_PTR, "__aligned_u64",
+ "Pointer to input data")
+ KAPI_FIELD_OFFSET(offsetof(struct fwctl_rpc, in))
+ KAPI_FIELD_SIZE(sizeof(__aligned_u64))
+ KAPI_STRUCT_FIELD_END
+
+ KAPI_STRUCT_FIELD(5, "out", KAPI_TYPE_PTR, "__aligned_u64",
+ "Pointer to output buffer")
+ KAPI_FIELD_OFFSET(offsetof(struct fwctl_rpc, out))
+ KAPI_FIELD_SIZE(sizeof(__aligned_u64))
+ KAPI_STRUCT_FIELD_END
+ KAPI_STRUCT_SPEC_END
+
+ KAPI_STRUCT_SPEC_COUNT(1)
+
+ /* Side effects */
+ KAPI_SIDE_EFFECT(0, KAPI_EFFECT_HARDWARE | KAPI_EFFECT_MODIFY_STATE,
+ "device firmware",
+ "May modify device configuration or firmware state")
+ KAPI_EFFECT_CONDITION("scope >= FWCTL_RPC_DEBUG_WRITE")
+ KAPI_SIDE_EFFECT_END
+
+ KAPI_SIDE_EFFECT(1, KAPI_EFFECT_MODIFY_STATE,
+ "kernel taint",
+ "Taints kernel with TAINT_FWCTL on first debug write")
+ KAPI_EFFECT_CONDITION("scope >= FWCTL_RPC_DEBUG_WRITE && first use")
+ KAPI_SIDE_EFFECT_END
+
+ KAPI_SIDE_EFFECT(2, KAPI_EFFECT_SCHEDULE,
+ "process",
+ "May block while firmware processes the RPC")
+ KAPI_EFFECT_CONDITION("firmware operation takes time")
+ KAPI_SIDE_EFFECT_END
+
+ KAPI_SIDE_EFFECT_COUNT(3)
+
+ /* State transitions */
+ KAPI_STATE_TRANS(0, "device state",
+ "current configuration", "modified configuration",
+ "Device configuration changed by RPC command")
+ KAPI_STATE_TRANS_COND("RPC modifies device settings")
+ KAPI_STATE_TRANS_END
+
+ KAPI_STATE_TRANS(1, "kernel taint state",
+ "untainted", "TAINT_FWCTL set",
+ "Kernel marked as tainted due to firmware modification")
+ KAPI_STATE_TRANS_COND("First debug write operation")
+ KAPI_STATE_TRANS_END
+
+ KAPI_STATE_TRANS_COUNT(2)
+ },
+};
+
+/* Register all fwctl IOCTL specifications */
+KAPI_IOCTL_SPEC_DRIVER("fwctl", {
+ &fwctl_info_spec,
+ &fwctl_rpc_spec,
+})
+
static void fwctl_device_release(struct device *device)
{
struct fwctl_device *fwctl =
@@ -325,7 +605,7 @@ struct fwctl_device *_fwctl_alloc_device(struct device *parent,
if (!fwctl)
return NULL;

- cdev_init(&fwctl->cdev, &fwctl_fops);
+ cdev_init(&fwctl->cdev, fwctl_fops);
/*
* The driver module is protected by fwctl_register/unregister(),
* unregister won't complete until we are done with the driver's module.
@@ -395,6 +675,9 @@ static int __init fwctl_init(void)
{
int ret;

+ /* Initialize the wrapped file_operations */
+ kapi_init_fops_fwctl_fops();
+
ret = alloc_chrdev_region(&fwctl_dev, 0, FWCTL_MAX_DEVICES, "fwctl");
if (ret)
return ret;
@@ -402,8 +685,15 @@ static int __init fwctl_init(void)
ret = class_register(&fwctl_class);
if (ret)
goto err_chrdev;
+
+ ret = kapi_ioctl_specs_init();
+ if (ret)
+ goto err_class;
+
return 0;

+err_class:
+ class_unregister(&fwctl_class);
err_chrdev:
unregister_chrdev_region(fwctl_dev, FWCTL_MAX_DEVICES);
return ret;
@@ -411,6 +701,7 @@ static int __init fwctl_init(void)

static void __exit fwctl_exit(void)
{
+ kapi_ioctl_specs_exit();
class_unregister(&fwctl_class);
unregister_chrdev_region(fwctl_dev, FWCTL_MAX_DEVICES);
}
--
2.39.5