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 #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 35 static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn) 36 { 37 return syscall_fn(regs); 38 } 39 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 72 static inline bool has_syscall_work(unsigned long flags) 73 { 74 return unlikely(flags & _TIF_SYSCALL_WORK); 75 } 76 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 } 152 153 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 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