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 #include <asm/unistd_compat_32.h> 18 19 long compat_arm_syscall(struct pt_regs *regs, int scno); 20 long sys_ni_syscall(void); 21 22 static long do_ni_syscall(struct pt_regs *regs, int scno) 23 { 24 if (is_compat_task()) { 25 long ret = compat_arm_syscall(regs, scno); 26 if (ret != -ENOSYS) 27 return ret; 28 } 29 30 return sys_ni_syscall(); 31 } 32 33 static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn) 34 { 35 return syscall_fn(regs); 36 } 37 38 static void invoke_syscall(struct pt_regs *regs, unsigned int scno, 39 unsigned int sc_nr, 40 const syscall_fn_t syscall_table[]) 41 { 42 long ret; 43 44 add_random_kstack_offset(); 45 46 if (likely(scno < sc_nr)) { 47 syscall_fn_t syscall_fn; 48 syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)]; 49 ret = __invoke_syscall(regs, syscall_fn); 50 } else { 51 ret = do_ni_syscall(regs, scno); 52 } 53 54 syscall_set_return_value(current, regs, 0, ret); 55 } 56 57 static inline bool has_syscall_work(unsigned long flags) 58 { 59 return unlikely(flags & _TIF_SYSCALL_WORK); 60 } 61 62 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, 63 const syscall_fn_t syscall_table[]) 64 { 65 unsigned long flags = read_thread_flags(); 66 67 regs->orig_x0 = regs->regs[0]; 68 regs->syscallno = scno; 69 70 /* 71 * BTI note: 72 * The architecture does not guarantee that SPSR.BTYPE is zero 73 * on taking an SVC, so we could return to userspace with a 74 * non-zero BTYPE after the syscall. 75 * 76 * This shouldn't matter except when userspace is explicitly 77 * doing something stupid, such as setting PROT_BTI on a page 78 * that lacks conforming BTI/PACIxSP instructions, falling 79 * through from one executable page to another with differing 80 * PROT_BTI, or messing with BTYPE via ptrace: in such cases, 81 * userspace should not be surprised if a SIGILL occurs on 82 * syscall return. 83 * 84 * So, don't touch regs->pstate & PSR_BTYPE_MASK here. 85 * (Similarly for HVC and SMC elsewhere.) 86 */ 87 88 if (unlikely(flags & _TIF_MTE_ASYNC_FAULT)) { 89 /* 90 * Process the asynchronous tag check fault before the actual 91 * syscall. do_notify_resume() will send a signal to userspace 92 * before the syscall is restarted. 93 */ 94 syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0); 95 return; 96 } 97 98 if (has_syscall_work(flags)) { 99 /* 100 * The de-facto standard way to skip a system call using ptrace 101 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a 102 * suitable error code for consumption by userspace. However, 103 * this cannot be distinguished from a user-issued syscall(-1) 104 * and so we must set x0 to -ENOSYS here in case the tracer doesn't 105 * issue the skip and we fall into trace_exit with x0 preserved. 106 * 107 * This is slightly odd because it also means that if a tracer 108 * sets the system call number to -1 but does not initialise x0, 109 * then x0 will be preserved for all system calls apart from a 110 * user-issued syscall(-1). However, requesting a skip and not 111 * setting the return value is unlikely to do anything sensible 112 * anyway. 113 */ 114 if (scno == NO_SYSCALL) 115 syscall_set_return_value(current, regs, -ENOSYS, 0); 116 scno = syscall_trace_enter(regs); 117 if (scno == NO_SYSCALL) 118 goto trace_exit; 119 } 120 121 invoke_syscall(regs, scno, sc_nr, syscall_table); 122 123 /* 124 * The tracing status may have changed under our feet, so we have to 125 * check again. However, if we were tracing entry, then we always trace 126 * exit regardless, as the old entry assembly did. 127 */ 128 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) { 129 flags = read_thread_flags(); 130 if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) 131 return; 132 } 133 134 trace_exit: 135 syscall_trace_exit(regs); 136 } 137 138 void do_el0_svc(struct pt_regs *regs) 139 { 140 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table); 141 } 142 143 #ifdef CONFIG_COMPAT 144 void do_el0_svc_compat(struct pt_regs *regs) 145 { 146 el0_svc_common(regs, regs->regs[7], __NR_compat32_syscalls, 147 compat_sys_call_table); 148 } 149 #endif 150