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/fpsimd.h> 13 #include <asm/syscall.h> 14 #include <asm/thread_info.h> 15 #include <asm/unistd.h> 16 17 long compat_arm_syscall(struct pt_regs *regs, int scno); 18 long sys_ni_syscall(void); 19 20 static long do_ni_syscall(struct pt_regs *regs, int scno) 21 { 22 #ifdef CONFIG_COMPAT 23 long ret; 24 if (is_compat_task()) { 25 ret = compat_arm_syscall(regs, scno); 26 if (ret != -ENOSYS) 27 return ret; 28 } 29 #endif 30 31 return sys_ni_syscall(); 32 } 33 34 static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn) 35 { 36 return syscall_fn(regs); 37 } 38 39 static void invoke_syscall(struct pt_regs *regs, unsigned int scno, 40 unsigned int sc_nr, 41 const syscall_fn_t syscall_table[]) 42 { 43 long ret; 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 if (is_compat_task()) 54 ret = lower_32_bits(ret); 55 56 regs->regs[0] = ret; 57 } 58 59 static inline bool has_syscall_work(unsigned long flags) 60 { 61 return unlikely(flags & _TIF_SYSCALL_WORK); 62 } 63 64 int syscall_trace_enter(struct pt_regs *regs); 65 void syscall_trace_exit(struct pt_regs *regs); 66 67 #ifdef CONFIG_ARM64_ERRATUM_1463225 68 DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa); 69 70 static void cortex_a76_erratum_1463225_svc_handler(void) 71 { 72 u32 reg, val; 73 74 if (!unlikely(test_thread_flag(TIF_SINGLESTEP))) 75 return; 76 77 if (!unlikely(this_cpu_has_cap(ARM64_WORKAROUND_1463225))) 78 return; 79 80 __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 1); 81 reg = read_sysreg(mdscr_el1); 82 val = reg | DBG_MDSCR_SS | DBG_MDSCR_KDE; 83 write_sysreg(val, mdscr_el1); 84 asm volatile("msr daifclr, #8"); 85 isb(); 86 87 /* We will have taken a single-step exception by this point */ 88 89 write_sysreg(reg, mdscr_el1); 90 __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 0); 91 } 92 #else 93 static void cortex_a76_erratum_1463225_svc_handler(void) { } 94 #endif /* CONFIG_ARM64_ERRATUM_1463225 */ 95 96 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, 97 const syscall_fn_t syscall_table[]) 98 { 99 unsigned long flags = current_thread_info()->flags; 100 101 regs->orig_x0 = regs->regs[0]; 102 regs->syscallno = scno; 103 104 /* 105 * BTI note: 106 * The architecture does not guarantee that SPSR.BTYPE is zero 107 * on taking an SVC, so we could return to userspace with a 108 * non-zero BTYPE after the syscall. 109 * 110 * This shouldn't matter except when userspace is explicitly 111 * doing something stupid, such as setting PROT_BTI on a page 112 * that lacks conforming BTI/PACIxSP instructions, falling 113 * through from one executable page to another with differing 114 * PROT_BTI, or messing with BTYPE via ptrace: in such cases, 115 * userspace should not be surprised if a SIGILL occurs on 116 * syscall return. 117 * 118 * So, don't touch regs->pstate & PSR_BTYPE_MASK here. 119 * (Similarly for HVC and SMC elsewhere.) 120 */ 121 122 cortex_a76_erratum_1463225_svc_handler(); 123 local_daif_restore(DAIF_PROCCTX); 124 user_exit(); 125 126 if (has_syscall_work(flags)) { 127 /* 128 * The de-facto standard way to skip a system call using ptrace 129 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a 130 * suitable error code for consumption by userspace. However, 131 * this cannot be distinguished from a user-issued syscall(-1) 132 * and so we must set x0 to -ENOSYS here in case the tracer doesn't 133 * issue the skip and we fall into trace_exit with x0 preserved. 134 * 135 * This is slightly odd because it also means that if a tracer 136 * sets the system call number to -1 but does not initialise x0, 137 * then x0 will be preserved for all system calls apart from a 138 * user-issued syscall(-1). However, requesting a skip and not 139 * setting the return value is unlikely to do anything sensible 140 * anyway. 141 */ 142 if (scno == NO_SYSCALL) 143 regs->regs[0] = -ENOSYS; 144 scno = syscall_trace_enter(regs); 145 if (scno == NO_SYSCALL) 146 goto trace_exit; 147 } 148 149 invoke_syscall(regs, scno, sc_nr, syscall_table); 150 151 /* 152 * The tracing status may have changed under our feet, so we have to 153 * check again. However, if we were tracing entry, then we always trace 154 * exit regardless, as the old entry assembly did. 155 */ 156 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) { 157 local_daif_mask(); 158 flags = current_thread_info()->flags; 159 if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) { 160 /* 161 * We're off to userspace, where interrupts are 162 * always enabled after we restore the flags from 163 * the SPSR. 164 */ 165 trace_hardirqs_on(); 166 return; 167 } 168 local_daif_restore(DAIF_PROCCTX); 169 } 170 171 trace_exit: 172 syscall_trace_exit(regs); 173 } 174 175 static inline void sve_user_discard(void) 176 { 177 if (!system_supports_sve()) 178 return; 179 180 clear_thread_flag(TIF_SVE); 181 182 /* 183 * task_fpsimd_load() won't be called to update CPACR_EL1 in 184 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only 185 * happens if a context switch or kernel_neon_begin() or context 186 * modification (sigreturn, ptrace) intervenes. 187 * So, ensure that CPACR_EL1 is already correct for the fast-path case. 188 */ 189 sve_user_disable(); 190 } 191 192 void do_el0_svc(struct pt_regs *regs) 193 { 194 sve_user_discard(); 195 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table); 196 } 197 198 #ifdef CONFIG_COMPAT 199 void do_el0_svc_compat(struct pt_regs *regs) 200 { 201 el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls, 202 compat_sys_call_table); 203 } 204 #endif 205