1 /* 2 * common.c - C code for kernel entry and exit 3 * Copyright (c) 2015 Andrew Lutomirski 4 * GPL v2 5 * 6 * Based on asm and ptrace code by many authors. The code here originated 7 * in ptrace.c and signal.c. 8 */ 9 10 #include <linux/kernel.h> 11 #include <linux/sched.h> 12 #include <linux/mm.h> 13 #include <linux/smp.h> 14 #include <linux/errno.h> 15 #include <linux/ptrace.h> 16 #include <linux/tracehook.h> 17 #include <linux/audit.h> 18 #include <linux/seccomp.h> 19 #include <linux/signal.h> 20 #include <linux/export.h> 21 #include <linux/context_tracking.h> 22 #include <linux/user-return-notifier.h> 23 #include <linux/uprobes.h> 24 25 #include <asm/desc.h> 26 #include <asm/traps.h> 27 #include <asm/vdso.h> 28 #include <asm/uaccess.h> 29 #include <asm/cpufeature.h> 30 31 #define CREATE_TRACE_POINTS 32 #include <trace/events/syscalls.h> 33 34 #ifdef CONFIG_CONTEXT_TRACKING 35 /* Called on entry from user mode with IRQs off. */ 36 __visible inline void enter_from_user_mode(void) 37 { 38 CT_WARN_ON(ct_state() != CONTEXT_USER); 39 user_exit_irqoff(); 40 } 41 #else 42 static inline void enter_from_user_mode(void) {} 43 #endif 44 45 static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) 46 { 47 #ifdef CONFIG_X86_64 48 if (arch == AUDIT_ARCH_X86_64) { 49 audit_syscall_entry(regs->orig_ax, regs->di, 50 regs->si, regs->dx, regs->r10); 51 } else 52 #endif 53 { 54 audit_syscall_entry(regs->orig_ax, regs->bx, 55 regs->cx, regs->dx, regs->si); 56 } 57 } 58 59 /* 60 * Returns the syscall nr to run (which should match regs->orig_ax) or -1 61 * to skip the syscall. 62 */ 63 static long syscall_trace_enter(struct pt_regs *regs) 64 { 65 u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64; 66 67 struct thread_info *ti = current_thread_info(); 68 unsigned long ret = 0; 69 bool emulated = false; 70 u32 work; 71 72 if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) 73 BUG_ON(regs != task_pt_regs(current)); 74 75 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY; 76 77 if (unlikely(work & _TIF_SYSCALL_EMU)) 78 emulated = true; 79 80 if ((emulated || (work & _TIF_SYSCALL_TRACE)) && 81 tracehook_report_syscall_entry(regs)) 82 return -1L; 83 84 if (emulated) 85 return -1L; 86 87 #ifdef CONFIG_SECCOMP 88 /* 89 * Do seccomp after ptrace, to catch any tracer changes. 90 */ 91 if (work & _TIF_SECCOMP) { 92 struct seccomp_data sd; 93 94 sd.arch = arch; 95 sd.nr = regs->orig_ax; 96 sd.instruction_pointer = regs->ip; 97 #ifdef CONFIG_X86_64 98 if (arch == AUDIT_ARCH_X86_64) { 99 sd.args[0] = regs->di; 100 sd.args[1] = regs->si; 101 sd.args[2] = regs->dx; 102 sd.args[3] = regs->r10; 103 sd.args[4] = regs->r8; 104 sd.args[5] = regs->r9; 105 } else 106 #endif 107 { 108 sd.args[0] = regs->bx; 109 sd.args[1] = regs->cx; 110 sd.args[2] = regs->dx; 111 sd.args[3] = regs->si; 112 sd.args[4] = regs->di; 113 sd.args[5] = regs->bp; 114 } 115 116 ret = __secure_computing(&sd); 117 if (ret == -1) 118 return ret; 119 } 120 #endif 121 122 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT))) 123 trace_sys_enter(regs, regs->orig_ax); 124 125 do_audit_syscall_entry(regs, arch); 126 127 return ret ?: regs->orig_ax; 128 } 129 130 #define EXIT_TO_USERMODE_LOOP_FLAGS \ 131 (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ 132 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY) 133 134 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) 135 { 136 /* 137 * In order to return to user mode, we need to have IRQs off with 138 * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY, 139 * _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags 140 * can be set at any time on preemptable kernels if we have IRQs on, 141 * so we need to loop. Disabling preemption wouldn't help: doing the 142 * work to clear some of the flags can sleep. 143 */ 144 while (true) { 145 /* We have work to do. */ 146 local_irq_enable(); 147 148 if (cached_flags & _TIF_NEED_RESCHED) 149 schedule(); 150 151 if (cached_flags & _TIF_UPROBE) 152 uprobe_notify_resume(regs); 153 154 /* deal with pending signal delivery */ 155 if (cached_flags & _TIF_SIGPENDING) 156 do_signal(regs); 157 158 if (cached_flags & _TIF_NOTIFY_RESUME) { 159 clear_thread_flag(TIF_NOTIFY_RESUME); 160 tracehook_notify_resume(regs); 161 } 162 163 if (cached_flags & _TIF_USER_RETURN_NOTIFY) 164 fire_user_return_notifiers(); 165 166 /* Disable IRQs and retry */ 167 local_irq_disable(); 168 169 cached_flags = READ_ONCE(current_thread_info()->flags); 170 171 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 172 break; 173 } 174 } 175 176 /* Called with IRQs disabled. */ 177 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) 178 { 179 struct thread_info *ti = current_thread_info(); 180 u32 cached_flags; 181 182 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled())) 183 local_irq_disable(); 184 185 lockdep_sys_exit(); 186 187 cached_flags = READ_ONCE(ti->flags); 188 189 if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 190 exit_to_usermode_loop(regs, cached_flags); 191 192 #ifdef CONFIG_COMPAT 193 /* 194 * Compat syscalls set TS_COMPAT. Make sure we clear it before 195 * returning to user mode. We need to clear it *after* signal 196 * handling, because syscall restart has a fixup for compat 197 * syscalls. The fixup is exercised by the ptrace_syscall_32 198 * selftest. 199 * 200 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer 201 * special case only applies after poking regs and before the 202 * very next return to user mode. 203 */ 204 current->thread.status &= ~(TS_COMPAT|TS_I386_REGS_POKED); 205 #endif 206 207 user_enter_irqoff(); 208 } 209 210 #define SYSCALL_EXIT_WORK_FLAGS \ 211 (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \ 212 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT) 213 214 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags) 215 { 216 bool step; 217 218 audit_syscall_exit(regs); 219 220 if (cached_flags & _TIF_SYSCALL_TRACEPOINT) 221 trace_sys_exit(regs, regs->ax); 222 223 /* 224 * If TIF_SYSCALL_EMU is set, we only get here because of 225 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP). 226 * We already reported this syscall instruction in 227 * syscall_trace_enter(). 228 */ 229 step = unlikely( 230 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)) 231 == _TIF_SINGLESTEP); 232 if (step || cached_flags & _TIF_SYSCALL_TRACE) 233 tracehook_report_syscall_exit(regs, step); 234 } 235 236 /* 237 * Called with IRQs on and fully valid regs. Returns with IRQs off in a 238 * state such that we can immediately switch to user mode. 239 */ 240 __visible inline void syscall_return_slowpath(struct pt_regs *regs) 241 { 242 struct thread_info *ti = current_thread_info(); 243 u32 cached_flags = READ_ONCE(ti->flags); 244 245 CT_WARN_ON(ct_state() != CONTEXT_KERNEL); 246 247 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && 248 WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax)) 249 local_irq_enable(); 250 251 /* 252 * First do one-time work. If these work items are enabled, we 253 * want to run them exactly once per syscall exit with IRQs on. 254 */ 255 if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS)) 256 syscall_slow_exit_work(regs, cached_flags); 257 258 local_irq_disable(); 259 prepare_exit_to_usermode(regs); 260 } 261 262 #ifdef CONFIG_X86_64 263 __visible void do_syscall_64(struct pt_regs *regs) 264 { 265 struct thread_info *ti = current_thread_info(); 266 unsigned long nr = regs->orig_ax; 267 268 enter_from_user_mode(); 269 local_irq_enable(); 270 271 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) 272 nr = syscall_trace_enter(regs); 273 274 /* 275 * NB: Native and x32 syscalls are dispatched from the same 276 * table. The only functional difference is the x32 bit in 277 * regs->orig_ax, which changes the behavior of some syscalls. 278 */ 279 if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) { 280 regs->ax = sys_call_table[nr & __SYSCALL_MASK]( 281 regs->di, regs->si, regs->dx, 282 regs->r10, regs->r8, regs->r9); 283 } 284 285 syscall_return_slowpath(regs); 286 } 287 #endif 288 289 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) 290 /* 291 * Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does 292 * all entry and exit work and returns with IRQs off. This function is 293 * extremely hot in workloads that use it, and it's usually called from 294 * do_fast_syscall_32, so forcibly inline it to improve performance. 295 */ 296 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) 297 { 298 struct thread_info *ti = current_thread_info(); 299 unsigned int nr = (unsigned int)regs->orig_ax; 300 301 #ifdef CONFIG_IA32_EMULATION 302 current->thread.status |= TS_COMPAT; 303 #endif 304 305 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) { 306 /* 307 * Subtlety here: if ptrace pokes something larger than 308 * 2^32-1 into orig_ax, this truncates it. This may or 309 * may not be necessary, but it matches the old asm 310 * behavior. 311 */ 312 nr = syscall_trace_enter(regs); 313 } 314 315 if (likely(nr < IA32_NR_syscalls)) { 316 /* 317 * It's possible that a 32-bit syscall implementation 318 * takes a 64-bit parameter but nonetheless assumes that 319 * the high bits are zero. Make sure we zero-extend all 320 * of the args. 321 */ 322 regs->ax = ia32_sys_call_table[nr]( 323 (unsigned int)regs->bx, (unsigned int)regs->cx, 324 (unsigned int)regs->dx, (unsigned int)regs->si, 325 (unsigned int)regs->di, (unsigned int)regs->bp); 326 } 327 328 syscall_return_slowpath(regs); 329 } 330 331 /* Handles int $0x80 */ 332 __visible void do_int80_syscall_32(struct pt_regs *regs) 333 { 334 enter_from_user_mode(); 335 local_irq_enable(); 336 do_syscall_32_irqs_on(regs); 337 } 338 339 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */ 340 __visible long do_fast_syscall_32(struct pt_regs *regs) 341 { 342 /* 343 * Called using the internal vDSO SYSENTER/SYSCALL32 calling 344 * convention. Adjust regs so it looks like we entered using int80. 345 */ 346 347 unsigned long landing_pad = (unsigned long)current->mm->context.vdso + 348 vdso_image_32.sym_int80_landing_pad; 349 350 /* 351 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward 352 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction. 353 * Fix it up. 354 */ 355 regs->ip = landing_pad; 356 357 enter_from_user_mode(); 358 359 local_irq_enable(); 360 361 /* Fetch EBP from where the vDSO stashed it. */ 362 if ( 363 #ifdef CONFIG_X86_64 364 /* 365 * Micro-optimization: the pointer we're following is explicitly 366 * 32 bits, so it can't be out of range. 367 */ 368 __get_user(*(u32 *)®s->bp, 369 (u32 __user __force *)(unsigned long)(u32)regs->sp) 370 #else 371 get_user(*(u32 *)®s->bp, 372 (u32 __user __force *)(unsigned long)(u32)regs->sp) 373 #endif 374 ) { 375 376 /* User code screwed up. */ 377 local_irq_disable(); 378 regs->ax = -EFAULT; 379 prepare_exit_to_usermode(regs); 380 return 0; /* Keep it simple: use IRET. */ 381 } 382 383 /* Now this is just like a normal syscall. */ 384 do_syscall_32_irqs_on(regs); 385 386 #ifdef CONFIG_X86_64 387 /* 388 * Opportunistic SYSRETL: if possible, try to return using SYSRETL. 389 * SYSRETL is available on all 64-bit CPUs, so we don't need to 390 * bother with SYSEXIT. 391 * 392 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, 393 * because the ECX fixup above will ensure that this is essentially 394 * never the case. 395 */ 396 return regs->cs == __USER32_CS && regs->ss == __USER_DS && 397 regs->ip == landing_pad && 398 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0; 399 #else 400 /* 401 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT. 402 * 403 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, 404 * because the ECX fixup above will ensure that this is essentially 405 * never the case. 406 * 407 * We don't allow syscalls at all from VM86 mode, but we still 408 * need to check VM, because we might be returning from sys_vm86. 409 */ 410 return static_cpu_has(X86_FEATURE_SEP) && 411 regs->cs == __USER_CS && regs->ss == __USER_DS && 412 regs->ip == landing_pad && 413 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0; 414 #endif 415 } 416 #endif 417