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