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 (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 * This value will get limited by KSTACK_OFFSET_MAX(), which is 10 58 * bits. The actual entropy will be further reduced by the compiler 59 * when applying stack alignment constraints: the AAPCS mandates a 60 * 16-byte aligned SP at function boundaries, which will remove the 61 * 4 low bits from any entropy chosen here. 62 * 63 * The resulting 6 bits of entropy is seen in SP[9:4]. 64 */ 65 choose_random_kstack_offset(get_random_u16()); 66 } 67 68 static inline bool has_syscall_work(unsigned long flags) 69 { 70 return unlikely(flags & _TIF_SYSCALL_WORK); 71 } 72 73 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, 74 const syscall_fn_t syscall_table[]) 75 { 76 unsigned long flags = read_thread_flags(); 77 78 regs->orig_x0 = regs->regs[0]; 79 regs->syscallno = scno; 80 81 /* 82 * BTI note: 83 * The architecture does not guarantee that SPSR.BTYPE is zero 84 * on taking an SVC, so we could return to userspace with a 85 * non-zero BTYPE after the syscall. 86 * 87 * This shouldn't matter except when userspace is explicitly 88 * doing something stupid, such as setting PROT_BTI on a page 89 * that lacks conforming BTI/PACIxSP instructions, falling 90 * through from one executable page to another with differing 91 * PROT_BTI, or messing with BTYPE via ptrace: in such cases, 92 * userspace should not be surprised if a SIGILL occurs on 93 * syscall return. 94 * 95 * So, don't touch regs->pstate & PSR_BTYPE_MASK here. 96 * (Similarly for HVC and SMC elsewhere.) 97 */ 98 99 if (flags & _TIF_MTE_ASYNC_FAULT) { 100 /* 101 * Process the asynchronous tag check fault before the actual 102 * syscall. do_notify_resume() will send a signal to userspace 103 * before the syscall is restarted. 104 */ 105 syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0); 106 return; 107 } 108 109 if (has_syscall_work(flags)) { 110 /* 111 * The de-facto standard way to skip a system call using ptrace 112 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a 113 * suitable error code for consumption by userspace. However, 114 * this cannot be distinguished from a user-issued syscall(-1) 115 * and so we must set x0 to -ENOSYS here in case the tracer doesn't 116 * issue the skip and we fall into trace_exit with x0 preserved. 117 * 118 * This is slightly odd because it also means that if a tracer 119 * sets the system call number to -1 but does not initialise x0, 120 * then x0 will be preserved for all system calls apart from a 121 * user-issued syscall(-1). However, requesting a skip and not 122 * setting the return value is unlikely to do anything sensible 123 * anyway. 124 */ 125 if (scno == NO_SYSCALL) 126 syscall_set_return_value(current, regs, -ENOSYS, 0); 127 scno = syscall_trace_enter(regs); 128 if (scno == NO_SYSCALL) 129 goto trace_exit; 130 } 131 132 invoke_syscall(regs, scno, sc_nr, syscall_table); 133 134 /* 135 * The tracing status may have changed under our feet, so we have to 136 * check again. However, if we were tracing entry, then we always trace 137 * exit regardless, as the old entry assembly did. 138 */ 139 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) { 140 flags = read_thread_flags(); 141 if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) 142 return; 143 } 144 145 trace_exit: 146 syscall_trace_exit(regs); 147 } 148 149 void do_el0_svc(struct pt_regs *regs) 150 { 151 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table); 152 } 153 154 #ifdef CONFIG_COMPAT 155 void do_el0_svc_compat(struct pt_regs *regs) 156 { 157 el0_svc_common(regs, regs->regs[7], __NR_compat32_syscalls, 158 compat_sys_call_table); 159 } 160 #endif 161