1 /*
2 * Copyright (c) 2017, Intel Corporation
3 *
4 * SPDX-License-Identifier: Apache-2.0
5 */
6
7
8 #ifndef ZEPHYR_INCLUDE_SYSCALL_H_
9 #define ZEPHYR_INCLUDE_SYSCALL_H_
10
11 #include <zephyr/syscall_list.h>
12 #include <zephyr/arch/syscall.h>
13 #include <stdbool.h>
14
15 #ifndef _ASMLANGUAGE
16 #include <zephyr/types.h>
17 #include <zephyr/linker/sections.h>
18
19 #ifdef __cplusplus
20 extern "C" {
21 #endif
22
23 /*
24 * System Call Declaration macros
25 *
26 * These macros are used in public header files to declare system calls.
27 * They generate inline functions which have different implementations
28 * depending on the current compilation context:
29 *
30 * - Kernel-only code, or CONFIG_USERSPACE disabled, these inlines will
31 * directly call the implementation
32 * - User-only code, these inlines will marshal parameters and elevate
33 * privileges
34 * - Mixed or indeterminate code, these inlines will do a runtime check
35 * to determine what course of action is needed.
36 *
37 * All system calls require a verifier function and an implementation
38 * function. These must follow a naming convention. For a system call
39 * named k_foo():
40 *
41 * - The handler function will be named z_vrfy_k_foo(). Handler
42 * functions have the same type signature as the wrapped call,
43 * verify arguments passed up from userspace, and call the
44 * implementation function. See documentation for that typedef for
45 * more information. - The implementation function will be named
46 * z_impl_k_foo(). This is the actual implementation of the system
47 * call.
48 */
49
50 /**
51 * @typedef _k_syscall_handler_t
52 * @brief System call handler function type
53 *
54 * These are kernel-side skeleton functions for system calls. They are
55 * necessary to sanitize the arguments passed into the system call:
56 *
57 * - Any kernel object or device pointers are validated with _SYSCALL_IS_OBJ()
58 * - Any memory buffers passed in are checked to ensure that the calling thread
59 * actually has access to them
60 * - Many kernel calls do no sanity checking of parameters other than
61 * assertions. The handler must check all of these conditions using
62 * _SYSCALL_ASSERT()
63 * - If the system call has more than 6 arguments, then arg6 will be a pointer
64 * to some struct containing arguments 6+. The struct itself needs to be
65 * validated like any other buffer passed in from userspace, and its members
66 * individually validated (if necessary) and then passed to the real
67 * implementation like normal arguments
68 *
69 * Even if the system call implementation has no return value, these always
70 * return something, even 0, to prevent register leakage to userspace.
71 *
72 * Once everything has been validated, the real implementation will be executed.
73 *
74 * @param arg1 system call argument 1
75 * @param arg2 system call argument 2
76 * @param arg3 system call argument 3
77 * @param arg4 system call argument 4
78 * @param arg5 system call argument 5
79 * @param arg6 system call argument 6
80 * @param ssf System call stack frame pointer. Used to generate kernel oops
81 * via _arch_syscall_oops_at(). Contents are arch-specific.
82 * @return system call return value, or 0 if the system call implementation
83 * return void
84 *
85 */
86 typedef uintptr_t (*_k_syscall_handler_t)(uintptr_t arg1, uintptr_t arg2,
87 uintptr_t arg3, uintptr_t arg4,
88 uintptr_t arg5, uintptr_t arg6,
89 void *ssf);
90
91 /* True if a syscall function must trap to the kernel, usually a
92 * compile-time decision.
93 */
z_syscall_trap(void)94 static ALWAYS_INLINE bool z_syscall_trap(void)
95 {
96 bool ret = false;
97 #ifdef CONFIG_USERSPACE
98 #if defined(__ZEPHYR_SUPERVISOR__)
99 ret = false;
100 #elif defined(__ZEPHYR_USER__)
101 ret = true;
102 #else
103 ret = arch_is_user_context();
104 #endif
105 #endif
106 return ret;
107 }
108
109 /**
110 * Indicate whether the CPU is currently in user mode
111 *
112 * @return true if the CPU is currently running with user permissions
113 */
114 __pinned_func
k_is_user_context(void)115 static inline bool k_is_user_context(void)
116 {
117 #ifdef CONFIG_USERSPACE
118 return arch_is_user_context();
119 #else
120 return false;
121 #endif
122 }
123
124 #ifdef __cplusplus
125 }
126 #endif
127
128 #endif /* _ASMLANGUAGE */
129
130 #endif
131
