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/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 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 if (is_compat_task()) 55 ret = lower_32_bits(ret); 56 57 regs->regs[0] = ret; 58 } 59 60 static inline bool has_syscall_work(unsigned long flags) 61 { 62 return unlikely(flags & _TIF_SYSCALL_WORK); 63 } 64 65 int syscall_trace_enter(struct pt_regs *regs); 66 void syscall_trace_exit(struct pt_regs *regs); 67 68 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, 69 const syscall_fn_t syscall_table[]) 70 { 71 unsigned long flags = current_thread_info()->flags; 72 73 regs->orig_x0 = regs->regs[0]; 74 regs->syscallno = scno; 75 76 /* 77 * BTI note: 78 * The architecture does not guarantee that SPSR.BTYPE is zero 79 * on taking an SVC, so we could return to userspace with a 80 * non-zero BTYPE after the syscall. 81 * 82 * This shouldn't matter except when userspace is explicitly 83 * doing something stupid, such as setting PROT_BTI on a page 84 * that lacks conforming BTI/PACIxSP instructions, falling 85 * through from one executable page to another with differing 86 * PROT_BTI, or messing with BTYPE via ptrace: in such cases, 87 * userspace should not be surprised if a SIGILL occurs on 88 * syscall return. 89 * 90 * So, don't touch regs->pstate & PSR_BTYPE_MASK here. 91 * (Similarly for HVC and SMC elsewhere.) 92 */ 93 94 local_daif_restore(DAIF_PROCCTX); 95 96 if (flags & _TIF_MTE_ASYNC_FAULT) { 97 /* 98 * Process the asynchronous tag check fault before the actual 99 * syscall. do_notify_resume() will send a signal to userspace 100 * before the syscall is restarted. 101 */ 102 regs->regs[0] = -ERESTARTNOINTR; 103 return; 104 } 105 106 if (has_syscall_work(flags)) { 107 /* 108 * The de-facto standard way to skip a system call using ptrace 109 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a 110 * suitable error code for consumption by userspace. However, 111 * this cannot be distinguished from a user-issued syscall(-1) 112 * and so we must set x0 to -ENOSYS here in case the tracer doesn't 113 * issue the skip and we fall into trace_exit with x0 preserved. 114 * 115 * This is slightly odd because it also means that if a tracer 116 * sets the system call number to -1 but does not initialise x0, 117 * then x0 will be preserved for all system calls apart from a 118 * user-issued syscall(-1). However, requesting a skip and not 119 * setting the return value is unlikely to do anything sensible 120 * anyway. 121 */ 122 if (scno == NO_SYSCALL) 123 regs->regs[0] = -ENOSYS; 124 scno = syscall_trace_enter(regs); 125 if (scno == NO_SYSCALL) 126 goto trace_exit; 127 } 128 129 invoke_syscall(regs, scno, sc_nr, syscall_table); 130 131 /* 132 * The tracing status may have changed under our feet, so we have to 133 * check again. However, if we were tracing entry, then we always trace 134 * exit regardless, as the old entry assembly did. 135 */ 136 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) { 137 local_daif_mask(); 138 flags = current_thread_info()->flags; 139 if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) 140 return; 141 local_daif_restore(DAIF_PROCCTX); 142 } 143 144 trace_exit: 145 syscall_trace_exit(regs); 146 } 147 148 static inline void sve_user_discard(void) 149 { 150 if (!system_supports_sve()) 151 return; 152 153 clear_thread_flag(TIF_SVE); 154 155 /* 156 * task_fpsimd_load() won't be called to update CPACR_EL1 in 157 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only 158 * happens if a context switch or kernel_neon_begin() or context 159 * modification (sigreturn, ptrace) intervenes. 160 * So, ensure that CPACR_EL1 is already correct for the fast-path case. 161 */ 162 sve_user_disable(); 163 } 164 165 void do_el0_svc(struct pt_regs *regs) 166 { 167 sve_user_discard(); 168 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table); 169 } 170 171 #ifdef CONFIG_COMPAT 172 void do_el0_svc_compat(struct pt_regs *regs) 173 { 174 el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls, 175 compat_sys_call_table); 176 } 177 #endif 178