Loading...
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
18long compat_arm_syscall(struct pt_regs *regs, int scno);
19long sys_ni_syscall(void);
20
21static 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
35static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
36{
37 return syscall_fn(regs);
38}
39
40static 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
72static inline bool has_syscall_work(unsigned long flags)
73{
74 return unlikely(flags & _TIF_SYSCALL_WORK);
75}
76
77static 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
149trace_exit:
150 syscall_trace_exit(regs);
151}
152
153void 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
159void 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
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/syscalls.h>
9
10#include <asm/daifflags.h>
11#include <asm/debug-monitors.h>
12#include <asm/fpsimd.h>
13#include <asm/syscall.h>
14#include <asm/thread_info.h>
15#include <asm/unistd.h>
16
17long compat_arm_syscall(struct pt_regs *regs, int scno);
18long sys_ni_syscall(void);
19
20static long do_ni_syscall(struct pt_regs *regs, int scno)
21{
22#ifdef CONFIG_COMPAT
23 long ret;
24 if (is_compat_task()) {
25 ret = compat_arm_syscall(regs, scno);
26 if (ret != -ENOSYS)
27 return ret;
28 }
29#endif
30
31 return sys_ni_syscall();
32}
33
34static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
35{
36 return syscall_fn(regs);
37}
38
39static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
40 unsigned int sc_nr,
41 const syscall_fn_t syscall_table[])
42{
43 long ret;
44
45 if (scno < sc_nr) {
46 syscall_fn_t syscall_fn;
47 syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
48 ret = __invoke_syscall(regs, syscall_fn);
49 } else {
50 ret = do_ni_syscall(regs, scno);
51 }
52
53 regs->regs[0] = ret;
54}
55
56static inline bool has_syscall_work(unsigned long flags)
57{
58 return unlikely(flags & _TIF_SYSCALL_WORK);
59}
60
61int syscall_trace_enter(struct pt_regs *regs);
62void syscall_trace_exit(struct pt_regs *regs);
63
64#ifdef CONFIG_ARM64_ERRATUM_1463225
65DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa);
66
67static void cortex_a76_erratum_1463225_svc_handler(void)
68{
69 u32 reg, val;
70
71 if (!unlikely(test_thread_flag(TIF_SINGLESTEP)))
72 return;
73
74 if (!unlikely(this_cpu_has_cap(ARM64_WORKAROUND_1463225)))
75 return;
76
77 __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 1);
78 reg = read_sysreg(mdscr_el1);
79 val = reg | DBG_MDSCR_SS | DBG_MDSCR_KDE;
80 write_sysreg(val, mdscr_el1);
81 asm volatile("msr daifclr, #8");
82 isb();
83
84 /* We will have taken a single-step exception by this point */
85
86 write_sysreg(reg, mdscr_el1);
87 __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 0);
88}
89#else
90static void cortex_a76_erratum_1463225_svc_handler(void) { }
91#endif /* CONFIG_ARM64_ERRATUM_1463225 */
92
93static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
94 const syscall_fn_t syscall_table[])
95{
96 unsigned long flags = current_thread_info()->flags;
97
98 regs->orig_x0 = regs->regs[0];
99 regs->syscallno = scno;
100
101 cortex_a76_erratum_1463225_svc_handler();
102 local_daif_restore(DAIF_PROCCTX);
103 user_exit();
104
105 if (has_syscall_work(flags)) {
106 /* set default errno for user-issued syscall(-1) */
107 if (scno == NO_SYSCALL)
108 regs->regs[0] = -ENOSYS;
109 scno = syscall_trace_enter(regs);
110 if (scno == NO_SYSCALL)
111 goto trace_exit;
112 }
113
114 invoke_syscall(regs, scno, sc_nr, syscall_table);
115
116 /*
117 * The tracing status may have changed under our feet, so we have to
118 * check again. However, if we were tracing entry, then we always trace
119 * exit regardless, as the old entry assembly did.
120 */
121 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
122 local_daif_mask();
123 flags = current_thread_info()->flags;
124 if (!has_syscall_work(flags)) {
125 /*
126 * We're off to userspace, where interrupts are
127 * always enabled after we restore the flags from
128 * the SPSR.
129 */
130 trace_hardirqs_on();
131 return;
132 }
133 local_daif_restore(DAIF_PROCCTX);
134 }
135
136trace_exit:
137 syscall_trace_exit(regs);
138}
139
140static inline void sve_user_discard(void)
141{
142 if (!system_supports_sve())
143 return;
144
145 clear_thread_flag(TIF_SVE);
146
147 /*
148 * task_fpsimd_load() won't be called to update CPACR_EL1 in
149 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only
150 * happens if a context switch or kernel_neon_begin() or context
151 * modification (sigreturn, ptrace) intervenes.
152 * So, ensure that CPACR_EL1 is already correct for the fast-path case.
153 */
154 sve_user_disable();
155}
156
157asmlinkage void el0_svc_handler(struct pt_regs *regs)
158{
159 sve_user_discard();
160 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
161}
162
163#ifdef CONFIG_COMPAT
164asmlinkage void el0_svc_compat_handler(struct pt_regs *regs)
165{
166 el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls,
167 compat_sys_call_table);
168}
169#endif