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 #ifdef CONFIG_ARM64_ERRATUM_1463225 69 DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa); 70 71 static void cortex_a76_erratum_1463225_svc_handler(void) 72 { 73 u32 reg, val; 74 75 if (!unlikely(test_thread_flag(TIF_SINGLESTEP))) 76 return; 77 78 if (!unlikely(this_cpu_has_cap(ARM64_WORKAROUND_1463225))) 79 return; 80 81 __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 1); 82 reg = read_sysreg(mdscr_el1); 83 val = reg | DBG_MDSCR_SS | DBG_MDSCR_KDE; 84 write_sysreg(val, mdscr_el1); 85 asm volatile("msr daifclr, #8"); 86 isb(); 87 88 /* We will have taken a single-step exception by this point */ 89 90 write_sysreg(reg, mdscr_el1); 91 __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 0); 92 } 93 #else 94 static void cortex_a76_erratum_1463225_svc_handler(void) { } 95 #endif /* CONFIG_ARM64_ERRATUM_1463225 */ 96 97 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, 98 const syscall_fn_t syscall_table[]) 99 { 100 unsigned long flags = current_thread_info()->flags; 101 102 regs->orig_x0 = regs->regs[0]; 103 regs->syscallno = scno; 104 105 /* 106 * BTI note: 107 * The architecture does not guarantee that SPSR.BTYPE is zero 108 * on taking an SVC, so we could return to userspace with a 109 * non-zero BTYPE after the syscall. 110 * 111 * This shouldn't matter except when userspace is explicitly 112 * doing something stupid, such as setting PROT_BTI on a page 113 * that lacks conforming BTI/PACIxSP instructions, falling 114 * through from one executable page to another with differing 115 * PROT_BTI, or messing with BTYPE via ptrace: in such cases, 116 * userspace should not be surprised if a SIGILL occurs on 117 * syscall return. 118 * 119 * So, don't touch regs->pstate & PSR_BTYPE_MASK here. 120 * (Similarly for HVC and SMC elsewhere.) 121 */ 122 123 cortex_a76_erratum_1463225_svc_handler(); 124 local_daif_restore(DAIF_PROCCTX); 125 126 if (flags & _TIF_MTE_ASYNC_FAULT) { 127 /* 128 * Process the asynchronous tag check fault before the actual 129 * syscall. do_notify_resume() will send a signal to userspace 130 * before the syscall is restarted. 131 */ 132 regs->regs[0] = -ERESTARTNOINTR; 133 return; 134 } 135 136 if (has_syscall_work(flags)) { 137 /* 138 * The de-facto standard way to skip a system call using ptrace 139 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a 140 * suitable error code for consumption by userspace. However, 141 * this cannot be distinguished from a user-issued syscall(-1) 142 * and so we must set x0 to -ENOSYS here in case the tracer doesn't 143 * issue the skip and we fall into trace_exit with x0 preserved. 144 * 145 * This is slightly odd because it also means that if a tracer 146 * sets the system call number to -1 but does not initialise x0, 147 * then x0 will be preserved for all system calls apart from a 148 * user-issued syscall(-1). However, requesting a skip and not 149 * setting the return value is unlikely to do anything sensible 150 * anyway. 151 */ 152 if (scno == NO_SYSCALL) 153 regs->regs[0] = -ENOSYS; 154 scno = syscall_trace_enter(regs); 155 if (scno == NO_SYSCALL) 156 goto trace_exit; 157 } 158 159 invoke_syscall(regs, scno, sc_nr, syscall_table); 160 161 /* 162 * The tracing status may have changed under our feet, so we have to 163 * check again. However, if we were tracing entry, then we always trace 164 * exit regardless, as the old entry assembly did. 165 */ 166 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) { 167 local_daif_mask(); 168 flags = current_thread_info()->flags; 169 if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) 170 return; 171 local_daif_restore(DAIF_PROCCTX); 172 } 173 174 trace_exit: 175 syscall_trace_exit(regs); 176 } 177 178 static inline void sve_user_discard(void) 179 { 180 if (!system_supports_sve()) 181 return; 182 183 clear_thread_flag(TIF_SVE); 184 185 /* 186 * task_fpsimd_load() won't be called to update CPACR_EL1 in 187 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only 188 * happens if a context switch or kernel_neon_begin() or context 189 * modification (sigreturn, ptrace) intervenes. 190 * So, ensure that CPACR_EL1 is already correct for the fast-path case. 191 */ 192 sve_user_disable(); 193 } 194 195 void do_el0_svc(struct pt_regs *regs) 196 { 197 sve_user_discard(); 198 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table); 199 } 200 201 #ifdef CONFIG_COMPAT 202 void do_el0_svc_compat(struct pt_regs *regs) 203 { 204 el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls, 205 compat_sys_call_table); 206 } 207 #endif 208