1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 2020 Collabora Ltd.
4 */
5#include <linux/sched.h>
6#include <linux/prctl.h>
7#include <linux/ptrace.h>
8#include <linux/syscall_user_dispatch.h>
9#include <linux/uaccess.h>
10#include <linux/signal.h>
11#include <linux/elf.h>
12
13#include <linux/sched/signal.h>
14#include <linux/sched/task_stack.h>
15
16#include <asm/syscall.h>
17
18#include "common.h"
19
20static void trigger_sigsys(struct pt_regs *regs)
21{
22 struct kernel_siginfo info;
23
24 clear_siginfo(info: &info);
25 info.si_signo = SIGSYS;
26 info.si_code = SYS_USER_DISPATCH;
27 info.si_call_addr = (void __user *)KSTK_EIP(current);
28 info.si_errno = 0;
29 info.si_arch = syscall_get_arch(current);
30 info.si_syscall = syscall_get_nr(current, regs);
31
32 force_sig_info(&info);
33}
34
35bool syscall_user_dispatch(struct pt_regs *regs)
36{
37 struct syscall_user_dispatch *sd = &current->syscall_dispatch;
38 char state;
39
40 if (likely(instruction_pointer(regs) - sd->offset < sd->len))
41 return false;
42
43 if (unlikely(arch_syscall_is_vdso_sigreturn(regs)))
44 return false;
45
46 if (likely(sd->selector)) {
47 /*
48 * access_ok() is performed once, at prctl time, when
49 * the selector is loaded by userspace.
50 */
51 if (unlikely(__get_user(state, sd->selector))) {
52 force_exit_sig(SIGSEGV);
53 return true;
54 }
55
56 if (likely(state == SYSCALL_DISPATCH_FILTER_ALLOW))
57 return false;
58
59 if (state != SYSCALL_DISPATCH_FILTER_BLOCK) {
60 force_exit_sig(SIGSYS);
61 return true;
62 }
63 }
64
65 sd->on_dispatch = true;
66 syscall_rollback(current, regs);
67 trigger_sigsys(regs);
68
69 return true;
70}
71
72static int task_set_syscall_user_dispatch(struct task_struct *task, unsigned long mode,
73 unsigned long offset, unsigned long len,
74 char __user *selector)
75{
76 switch (mode) {
77 case PR_SYS_DISPATCH_OFF:
78 if (offset || len || selector)
79 return -EINVAL;
80 break;
81 case PR_SYS_DISPATCH_ON:
82 /*
83 * Validate the direct dispatcher region just for basic
84 * sanity against overflow and a 0-sized dispatcher
85 * region. If the user is able to submit a syscall from
86 * an address, that address is obviously valid.
87 */
88 if (offset && offset + len <= offset)
89 return -EINVAL;
90
91 /*
92 * access_ok() will clear memory tags for tagged addresses
93 * if current has memory tagging enabled.
94
95 * To enable a tracer to set a tracees selector the
96 * selector address must be untagged for access_ok(),
97 * otherwise an untagged tracer will always fail to set a
98 * tagged tracees selector.
99 */
100 if (selector && !access_ok(untagged_addr(selector), sizeof(*selector)))
101 return -EFAULT;
102
103 break;
104 default:
105 return -EINVAL;
106 }
107
108 task->syscall_dispatch.selector = selector;
109 task->syscall_dispatch.offset = offset;
110 task->syscall_dispatch.len = len;
111 task->syscall_dispatch.on_dispatch = false;
112
113 if (mode == PR_SYS_DISPATCH_ON)
114 set_task_syscall_work(task, SYSCALL_USER_DISPATCH);
115 else
116 clear_task_syscall_work(task, SYSCALL_USER_DISPATCH);
117
118 return 0;
119}
120
121int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
122 unsigned long len, char __user *selector)
123{
124 return task_set_syscall_user_dispatch(current, mode, offset, len, selector);
125}
126
127int syscall_user_dispatch_get_config(struct task_struct *task, unsigned long size,
128 void __user *data)
129{
130 struct syscall_user_dispatch *sd = &task->syscall_dispatch;
131 struct ptrace_sud_config cfg;
132
133 if (size != sizeof(cfg))
134 return -EINVAL;
135
136 if (test_task_syscall_work(task, SYSCALL_USER_DISPATCH))
137 cfg.mode = PR_SYS_DISPATCH_ON;
138 else
139 cfg.mode = PR_SYS_DISPATCH_OFF;
140
141 cfg.offset = sd->offset;
142 cfg.len = sd->len;
143 cfg.selector = (__u64)(uintptr_t)sd->selector;
144
145 if (copy_to_user(to: data, from: &cfg, n: sizeof(cfg)))
146 return -EFAULT;
147
148 return 0;
149}
150
151int syscall_user_dispatch_set_config(struct task_struct *task, unsigned long size,
152 void __user *data)
153{
154 struct ptrace_sud_config cfg;
155
156 if (size != sizeof(cfg))
157 return -EINVAL;
158
159 if (copy_from_user(to: &cfg, from: data, n: sizeof(cfg)))
160 return -EFAULT;
161
162 return task_set_syscall_user_dispatch(task, mode: cfg.mode, offset: cfg.offset, len: cfg.len,
163 selector: (char __user *)(uintptr_t)cfg.selector);
164}
165

source code of linux/kernel/entry/syscall_user_dispatch.c