1 // SPDX-License-Identifier: GPL-2.0
2
3 #include <linux/compiler.h>
4 #include <linux/context_tracking.h>
5 #include <linux/errno.h>
6 #include <linux/nospec.h>
7 #include <linux/ptrace.h>
8 #include <linux/randomize_kstack.h>
9 #include <linux/syscalls.h>
10
11 #include <asm/debug-monitors.h>
12 #include <asm/exception.h>
13 #include <asm/fpsimd.h>
14 #include <asm/syscall.h>
15 #include <asm/thread_info.h>
16 #include <asm/unistd.h>
17
18 long compat_arm_syscall(struct pt_regs *regs, int scno);
19 long sys_ni_syscall(void);
20
do_ni_syscall(struct pt_regs * regs,int scno)21 static long do_ni_syscall(struct pt_regs *regs, int scno)
22 {
23 #ifdef CONFIG_COMPAT
24 long ret;
25 if (is_compat_task()) {
26 ret = compat_arm_syscall(regs, scno);
27 if (ret != -ENOSYS)
28 return ret;
29 }
30 #endif
31
32 return sys_ni_syscall();
33 }
34
__invoke_syscall(struct pt_regs * regs,syscall_fn_t syscall_fn)35 static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
36 {
37 return syscall_fn(regs);
38 }
39
invoke_syscall(struct pt_regs * regs,unsigned int scno,unsigned int sc_nr,const syscall_fn_t syscall_table[])40 static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
41 unsigned int sc_nr,
42 const syscall_fn_t syscall_table[])
43 {
44 long ret;
45
46 add_random_kstack_offset();
47
48 if (scno < sc_nr) {
49 syscall_fn_t syscall_fn;
50 syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
51 ret = __invoke_syscall(regs, syscall_fn);
52 } else {
53 ret = do_ni_syscall(regs, scno);
54 }
55
56 syscall_set_return_value(current, regs, 0, ret);
57
58 /*
59 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
60 * but not enough for arm64 stack utilization comfort. To keep
61 * reasonable stack head room, reduce the maximum offset to 9 bits.
62 *
63 * The actual entropy will be further reduced by the compiler when
64 * applying stack alignment constraints: the AAPCS mandates a
65 * 16-byte (i.e. 4-bit) aligned SP at function boundaries.
66 *
67 * The resulting 5 bits of entropy is seen in SP[8:4].
68 */
69 choose_random_kstack_offset(get_random_u16() & 0x1FF);
70 }
71
has_syscall_work(unsigned long flags)72 static inline bool has_syscall_work(unsigned long flags)
73 {
74 return unlikely(flags & _TIF_SYSCALL_WORK);
75 }
76
el0_svc_common(struct pt_regs * regs,int scno,int sc_nr,const syscall_fn_t syscall_table[])77 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
78 const syscall_fn_t syscall_table[])
79 {
80 unsigned long flags = read_thread_flags();
81
82 regs->orig_x0 = regs->regs[0];
83 regs->syscallno = scno;
84
85 /*
86 * BTI note:
87 * The architecture does not guarantee that SPSR.BTYPE is zero
88 * on taking an SVC, so we could return to userspace with a
89 * non-zero BTYPE after the syscall.
90 *
91 * This shouldn't matter except when userspace is explicitly
92 * doing something stupid, such as setting PROT_BTI on a page
93 * that lacks conforming BTI/PACIxSP instructions, falling
94 * through from one executable page to another with differing
95 * PROT_BTI, or messing with BTYPE via ptrace: in such cases,
96 * userspace should not be surprised if a SIGILL occurs on
97 * syscall return.
98 *
99 * So, don't touch regs->pstate & PSR_BTYPE_MASK here.
100 * (Similarly for HVC and SMC elsewhere.)
101 */
102
103 if (flags & _TIF_MTE_ASYNC_FAULT) {
104 /*
105 * Process the asynchronous tag check fault before the actual
106 * syscall. do_notify_resume() will send a signal to userspace
107 * before the syscall is restarted.
108 */
109 syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0);
110 return;
111 }
112
113 if (has_syscall_work(flags)) {
114 /*
115 * The de-facto standard way to skip a system call using ptrace
116 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a
117 * suitable error code for consumption by userspace. However,
118 * this cannot be distinguished from a user-issued syscall(-1)
119 * and so we must set x0 to -ENOSYS here in case the tracer doesn't
120 * issue the skip and we fall into trace_exit with x0 preserved.
121 *
122 * This is slightly odd because it also means that if a tracer
123 * sets the system call number to -1 but does not initialise x0,
124 * then x0 will be preserved for all system calls apart from a
125 * user-issued syscall(-1). However, requesting a skip and not
126 * setting the return value is unlikely to do anything sensible
127 * anyway.
128 */
129 if (scno == NO_SYSCALL)
130 syscall_set_return_value(current, regs, -ENOSYS, 0);
131 scno = syscall_trace_enter(regs);
132 if (scno == NO_SYSCALL)
133 goto trace_exit;
134 }
135
136 invoke_syscall(regs, scno, sc_nr, syscall_table);
137
138 /*
139 * The tracing status may have changed under our feet, so we have to
140 * check again. However, if we were tracing entry, then we always trace
141 * exit regardless, as the old entry assembly did.
142 */
143 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
144 flags = read_thread_flags();
145 if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
146 return;
147 }
148
149 trace_exit:
150 syscall_trace_exit(regs);
151 }
152
do_el0_svc(struct pt_regs * regs)153 void do_el0_svc(struct pt_regs *regs)
154 {
155 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
156 }
157
158 #ifdef CONFIG_COMPAT
do_el0_svc_compat(struct pt_regs * regs)159 void do_el0_svc_compat(struct pt_regs *regs)
160 {
161 el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls,
162 compat_sys_call_table);
163 }
164 #endif
165