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
trigger_sigsys(struct pt_regs * regs)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
syscall_user_dispatch(struct pt_regs * regs)34 bool syscall_user_dispatch(struct pt_regs *regs)
35 {
36 struct syscall_user_dispatch *sd = ¤t->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
set_syscall_user_dispatch(unsigned long mode,unsigned long offset,unsigned long len,char __user * selector)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