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/daifflags.h> 12 #include <asm/debug-monitors.h> 13 #include <asm/exception.h> 14 #include <asm/fpsimd.h> 15 #include <asm/syscall.h> 16 #include <asm/thread_info.h> 17 #include <asm/unistd.h> 18 19 long compat_arm_syscall(struct pt_regs *regs, int scno); 20 long sys_ni_syscall(void); 21 22 static long do_ni_syscall(struct pt_regs *regs, int scno) 23 { 24 #ifdef CONFIG_COMPAT 25 long ret; 26 if (is_compat_task()) { 27 ret = compat_arm_syscall(regs, scno); 28 if (ret != -ENOSYS) 29 return ret; 30 } 31 #endif 32 33 return sys_ni_syscall(); 34 } 35 36 static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn) 37 { 38 return syscall_fn(regs); 39 } 40 41 static void invoke_syscall(struct pt_regs *regs, unsigned int scno, 42 unsigned int sc_nr, 43 const syscall_fn_t syscall_table[]) 44 { 45 long ret; 46 47 add_random_kstack_offset(); 48 49 if (scno < sc_nr) { 50 syscall_fn_t syscall_fn; 51 syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)]; 52 ret = __invoke_syscall(regs, syscall_fn); 53 } else { 54 ret = do_ni_syscall(regs, scno); 55 } 56 57 if (is_compat_task()) 58 ret = lower_32_bits(ret); 59 60 regs->regs[0] = ret; 61 62 /* 63 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), 64 * but not enough for arm64 stack utilization comfort. To keep 65 * reasonable stack head room, reduce the maximum offset to 9 bits. 66 * 67 * The actual entropy will be further reduced by the compiler when 68 * applying stack alignment constraints: the AAPCS mandates a 69 * 16-byte (i.e. 4-bit) aligned SP at function boundaries. 70 * 71 * The resulting 5 bits of entropy is seen in SP[8:4]. 72 */ 73 choose_random_kstack_offset(get_random_int() & 0x1FF); 74 } 75 76 static inline bool has_syscall_work(unsigned long flags) 77 { 78 return unlikely(flags & _TIF_SYSCALL_WORK); 79 } 80 81 int syscall_trace_enter(struct pt_regs *regs); 82 void syscall_trace_exit(struct pt_regs *regs); 83 84 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, 85 const syscall_fn_t syscall_table[]) 86 { 87 unsigned long flags = current_thread_info()->flags; 88 89 regs->orig_x0 = regs->regs[0]; 90 regs->syscallno = scno; 91 92 /* 93 * BTI note: 94 * The architecture does not guarantee that SPSR.BTYPE is zero 95 * on taking an SVC, so we could return to userspace with a 96 * non-zero BTYPE after the syscall. 97 * 98 * This shouldn't matter except when userspace is explicitly 99 * doing something stupid, such as setting PROT_BTI on a page 100 * that lacks conforming BTI/PACIxSP instructions, falling 101 * through from one executable page to another with differing 102 * PROT_BTI, or messing with BTYPE via ptrace: in such cases, 103 * userspace should not be surprised if a SIGILL occurs on 104 * syscall return. 105 * 106 * So, don't touch regs->pstate & PSR_BTYPE_MASK here. 107 * (Similarly for HVC and SMC elsewhere.) 108 */ 109 110 local_daif_restore(DAIF_PROCCTX); 111 112 if (flags & _TIF_MTE_ASYNC_FAULT) { 113 /* 114 * Process the asynchronous tag check fault before the actual 115 * syscall. do_notify_resume() will send a signal to userspace 116 * before the syscall is restarted. 117 */ 118 regs->regs[0] = -ERESTARTNOINTR; 119 return; 120 } 121 122 if (has_syscall_work(flags)) { 123 /* 124 * The de-facto standard way to skip a system call using ptrace 125 * is to set the system call to -1 (NO_SYSCALL) and set x0 to a 126 * suitable error code for consumption by userspace. However, 127 * this cannot be distinguished from a user-issued syscall(-1) 128 * and so we must set x0 to -ENOSYS here in case the tracer doesn't 129 * issue the skip and we fall into trace_exit with x0 preserved. 130 * 131 * This is slightly odd because it also means that if a tracer 132 * sets the system call number to -1 but does not initialise x0, 133 * then x0 will be preserved for all system calls apart from a 134 * user-issued syscall(-1). However, requesting a skip and not 135 * setting the return value is unlikely to do anything sensible 136 * anyway. 137 */ 138 if (scno == NO_SYSCALL) 139 regs->regs[0] = -ENOSYS; 140 scno = syscall_trace_enter(regs); 141 if (scno == NO_SYSCALL) 142 goto trace_exit; 143 } 144 145 invoke_syscall(regs, scno, sc_nr, syscall_table); 146 147 /* 148 * The tracing status may have changed under our feet, so we have to 149 * check again. However, if we were tracing entry, then we always trace 150 * exit regardless, as the old entry assembly did. 151 */ 152 if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) { 153 local_daif_mask(); 154 flags = current_thread_info()->flags; 155 if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) 156 return; 157 local_daif_restore(DAIF_PROCCTX); 158 } 159 160 trace_exit: 161 syscall_trace_exit(regs); 162 } 163 164 static inline void sve_user_discard(void) 165 { 166 if (!system_supports_sve()) 167 return; 168 169 clear_thread_flag(TIF_SVE); 170 171 /* 172 * task_fpsimd_load() won't be called to update CPACR_EL1 in 173 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only 174 * happens if a context switch or kernel_neon_begin() or context 175 * modification (sigreturn, ptrace) intervenes. 176 * So, ensure that CPACR_EL1 is already correct for the fast-path case. 177 */ 178 sve_user_disable(); 179 } 180 181 void do_el0_svc(struct pt_regs *regs) 182 { 183 sve_user_discard(); 184 el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table); 185 } 186 187 #ifdef CONFIG_COMPAT 188 void do_el0_svc_compat(struct pt_regs *regs) 189 { 190 el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls, 191 compat_sys_call_table); 192 } 193 #endif 194