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/syscall_user_dispatch.h>
8 #include <linux/uaccess.h>
9 #include <linux/signal.h>
10 #include <linux/elf.h>
11 
12 #include <linux/sched/signal.h>
13 #include <linux/sched/task_stack.h>
14 
15 #include <asm/syscall.h>
16 
17 #include "common.h"
18 
19 static void trigger_sigsys(struct pt_regs *regs)
20 {
21 	struct kernel_siginfo info;
22 
23 	clear_siginfo(&info);
24 	info.si_signo = SIGSYS;
25 	info.si_code = SYS_USER_DISPATCH;
26 	info.si_call_addr = (void __user *)KSTK_EIP(current);
27 	info.si_errno = 0;
28 	info.si_arch = syscall_get_arch(current);
29 	info.si_syscall = syscall_get_nr(current, regs);
30 
31 	force_sig_info(&info);
32 }
33 
34 bool syscall_user_dispatch(struct pt_regs *regs)
35 {
36 	struct syscall_user_dispatch *sd = &current->syscall_dispatch;
37 	char state;
38 
39 	if (likely(instruction_pointer(regs) - sd->offset < sd->len))
40 		return false;
41 
42 	if (unlikely(arch_syscall_is_vdso_sigreturn(regs)))
43 		return false;
44 
45 	if (likely(sd->selector)) {
46 		/*
47 		 * access_ok() is performed once, at prctl time, when
48 		 * the selector is loaded by userspace.
49 		 */
50 		if (unlikely(__get_user(state, sd->selector))) {
51 			force_exit_sig(SIGSEGV);
52 			return true;
53 		}
54 
55 		if (likely(state == SYSCALL_DISPATCH_FILTER_ALLOW))
56 			return false;
57 
58 		if (state != SYSCALL_DISPATCH_FILTER_BLOCK) {
59 			force_exit_sig(SIGSYS);
60 			return true;
61 		}
62 	}
63 
64 	sd->on_dispatch = true;
65 	syscall_rollback(current, regs);
66 	trigger_sigsys(regs);
67 
68 	return true;
69 }
70 
71 int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
72 			      unsigned long len, char __user *selector)
73 {
74 	switch (mode) {
75 	case PR_SYS_DISPATCH_OFF:
76 		if (offset || len || selector)
77 			return -EINVAL;
78 		break;
79 	case PR_SYS_DISPATCH_ON:
80 		/*
81 		 * Validate the direct dispatcher region just for basic
82 		 * sanity against overflow and a 0-sized dispatcher
83 		 * region.  If the user is able to submit a syscall from
84 		 * an address, that address is obviously valid.
85 		 */
86 		if (offset && offset + len <= offset)
87 			return -EINVAL;
88 
89 		if (selector && !access_ok(selector, sizeof(*selector)))
90 			return -EFAULT;
91 
92 		break;
93 	default:
94 		return -EINVAL;
95 	}
96 
97 	current->syscall_dispatch.selector = selector;
98 	current->syscall_dispatch.offset = offset;
99 	current->syscall_dispatch.len = len;
100 	current->syscall_dispatch.on_dispatch = false;
101 
102 	if (mode == PR_SYS_DISPATCH_ON)
103 		set_syscall_work(SYSCALL_USER_DISPATCH);
104 	else
105 		clear_syscall_work(SYSCALL_USER_DISPATCH);
106 
107 	return 0;
108 }
109