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/sched/task_stack.h> 13 #include <linux/mm.h> 14 #include <linux/smp.h> 15 #include <linux/errno.h> 16 #include <linux/ptrace.h> 17 #include <linux/tracehook.h> 18 #include <linux/audit.h> 19 #include <linux/seccomp.h> 20 #include <linux/signal.h> 21 #include <linux/export.h> 22 #include <linux/context_tracking.h> 23 #include <linux/user-return-notifier.h> 24 #include <linux/uprobes.h> 25 26 #include <asm/desc.h> 27 #include <asm/traps.h> 28 #include <asm/vdso.h> 29 #include <linux/uaccess.h> 30 #include <asm/cpufeature.h> 31 32 #define CREATE_TRACE_POINTS 33 #include <trace/events/syscalls.h> 34 35 #ifdef CONFIG_CONTEXT_TRACKING 36 /* Called on entry from user mode with IRQs off. */ 37 __visible inline void enter_from_user_mode(void) 38 { 39 CT_WARN_ON(ct_state() != CONTEXT_USER); 40 user_exit_irqoff(); 41 } 42 #else 43 static inline void enter_from_user_mode(void) {} 44 #endif 45 46 static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) 47 { 48 #ifdef CONFIG_X86_64 49 if (arch == AUDIT_ARCH_X86_64) { 50 audit_syscall_entry(regs->orig_ax, regs->di, 51 regs->si, regs->dx, regs->r10); 52 } else 53 #endif 54 { 55 audit_syscall_entry(regs->orig_ax, regs->bx, 56 regs->cx, regs->dx, regs->si); 57 } 58 } 59 60 /* 61 * Returns the syscall nr to run (which should match regs->orig_ax) or -1 62 * to skip the syscall. 63 */ 64 static long syscall_trace_enter(struct pt_regs *regs) 65 { 66 u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64; 67 68 struct thread_info *ti = current_thread_info(); 69 unsigned long ret = 0; 70 bool emulated = false; 71 u32 work; 72 73 if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) 74 BUG_ON(regs != task_pt_regs(current)); 75 76 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY; 77 78 if (unlikely(work & _TIF_SYSCALL_EMU)) 79 emulated = true; 80 81 if ((emulated || (work & _TIF_SYSCALL_TRACE)) && 82 tracehook_report_syscall_entry(regs)) 83 return -1L; 84 85 if (emulated) 86 return -1L; 87 88 #ifdef CONFIG_SECCOMP 89 /* 90 * Do seccomp after ptrace, to catch any tracer changes. 91 */ 92 if (work & _TIF_SECCOMP) { 93 struct seccomp_data sd; 94 95 sd.arch = arch; 96 sd.nr = regs->orig_ax; 97 sd.instruction_pointer = regs->ip; 98 #ifdef CONFIG_X86_64 99 if (arch == AUDIT_ARCH_X86_64) { 100 sd.args[0] = regs->di; 101 sd.args[1] = regs->si; 102 sd.args[2] = regs->dx; 103 sd.args[3] = regs->r10; 104 sd.args[4] = regs->r8; 105 sd.args[5] = regs->r9; 106 } else 107 #endif 108 { 109 sd.args[0] = regs->bx; 110 sd.args[1] = regs->cx; 111 sd.args[2] = regs->dx; 112 sd.args[3] = regs->si; 113 sd.args[4] = regs->di; 114 sd.args[5] = regs->bp; 115 } 116 117 ret = __secure_computing(&sd); 118 if (ret == -1) 119 return ret; 120 } 121 #endif 122 123 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT))) 124 trace_sys_enter(regs, regs->orig_ax); 125 126 do_audit_syscall_entry(regs, arch); 127 128 return ret ?: regs->orig_ax; 129 } 130 131 #define EXIT_TO_USERMODE_LOOP_FLAGS \ 132 (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ 133 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY) 134 135 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) 136 { 137 /* 138 * In order to return to user mode, we need to have IRQs off with 139 * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY, 140 * _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags 141 * can be set at any time on preemptable kernels if we have IRQs on, 142 * so we need to loop. Disabling preemption wouldn't help: doing the 143 * work to clear some of the flags can sleep. 144 */ 145 while (true) { 146 /* We have work to do. */ 147 local_irq_enable(); 148 149 if (cached_flags & _TIF_NEED_RESCHED) 150 schedule(); 151 152 if (cached_flags & _TIF_UPROBE) 153 uprobe_notify_resume(regs); 154 155 /* deal with pending signal delivery */ 156 if (cached_flags & _TIF_SIGPENDING) 157 do_signal(regs); 158 159 if (cached_flags & _TIF_NOTIFY_RESUME) { 160 clear_thread_flag(TIF_NOTIFY_RESUME); 161 tracehook_notify_resume(regs); 162 } 163 164 if (cached_flags & _TIF_USER_RETURN_NOTIFY) 165 fire_user_return_notifiers(); 166 167 /* Disable IRQs and retry */ 168 local_irq_disable(); 169 170 cached_flags = READ_ONCE(current_thread_info()->flags); 171 172 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 173 break; 174 } 175 } 176 177 /* Called with IRQs disabled. */ 178 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) 179 { 180 struct thread_info *ti = current_thread_info(); 181 u32 cached_flags; 182 183 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled())) 184 local_irq_disable(); 185 186 lockdep_sys_exit(); 187 188 cached_flags = READ_ONCE(ti->flags); 189 190 if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 191 exit_to_usermode_loop(regs, cached_flags); 192 193 #ifdef CONFIG_COMPAT 194 /* 195 * Compat syscalls set TS_COMPAT. Make sure we clear it before 196 * returning to user mode. We need to clear it *after* signal 197 * handling, because syscall restart has a fixup for compat 198 * syscalls. The fixup is exercised by the ptrace_syscall_32 199 * selftest. 200 * 201 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer 202 * special case only applies after poking regs and before the 203 * very next return to user mode. 204 */ 205 current->thread.status &= ~(TS_COMPAT|TS_I386_REGS_POKED); 206 #endif 207 208 user_enter_irqoff(); 209 } 210 211 #define SYSCALL_EXIT_WORK_FLAGS \ 212 (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \ 213 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT) 214 215 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags) 216 { 217 bool step; 218 219 audit_syscall_exit(regs); 220 221 if (cached_flags & _TIF_SYSCALL_TRACEPOINT) 222 trace_sys_exit(regs, regs->ax); 223 224 /* 225 * If TIF_SYSCALL_EMU is set, we only get here because of 226 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP). 227 * We already reported this syscall instruction in 228 * syscall_trace_enter(). 229 */ 230 step = unlikely( 231 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)) 232 == _TIF_SINGLESTEP); 233 if (step || cached_flags & _TIF_SYSCALL_TRACE) 234 tracehook_report_syscall_exit(regs, step); 235 } 236 237 /* 238 * Called with IRQs on and fully valid regs. Returns with IRQs off in a 239 * state such that we can immediately switch to user mode. 240 */ 241 __visible inline void syscall_return_slowpath(struct pt_regs *regs) 242 { 243 struct thread_info *ti = current_thread_info(); 244 u32 cached_flags = READ_ONCE(ti->flags); 245 246 CT_WARN_ON(ct_state() != CONTEXT_KERNEL); 247 248 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && 249 WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax)) 250 local_irq_enable(); 251 252 /* 253 * First do one-time work. If these work items are enabled, we 254 * want to run them exactly once per syscall exit with IRQs on. 255 */ 256 if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS)) 257 syscall_slow_exit_work(regs, cached_flags); 258 259 local_irq_disable(); 260 prepare_exit_to_usermode(regs); 261 } 262 263 #ifdef CONFIG_X86_64 264 __visible void do_syscall_64(struct pt_regs *regs) 265 { 266 struct thread_info *ti = current_thread_info(); 267 unsigned long nr = regs->orig_ax; 268 269 enter_from_user_mode(); 270 local_irq_enable(); 271 272 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) 273 nr = syscall_trace_enter(regs); 274 275 /* 276 * NB: Native and x32 syscalls are dispatched from the same 277 * table. The only functional difference is the x32 bit in 278 * regs->orig_ax, which changes the behavior of some syscalls. 279 */ 280 if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) { 281 regs->ax = sys_call_table[nr & __SYSCALL_MASK]( 282 regs->di, regs->si, regs->dx, 283 regs->r10, regs->r8, regs->r9); 284 } 285 286 syscall_return_slowpath(regs); 287 } 288 #endif 289 290 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) 291 /* 292 * Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does 293 * all entry and exit work and returns with IRQs off. This function is 294 * extremely hot in workloads that use it, and it's usually called from 295 * do_fast_syscall_32, so forcibly inline it to improve performance. 296 */ 297 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) 298 { 299 struct thread_info *ti = current_thread_info(); 300 unsigned int nr = (unsigned int)regs->orig_ax; 301 302 #ifdef CONFIG_IA32_EMULATION 303 current->thread.status |= TS_COMPAT; 304 #endif 305 306 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) { 307 /* 308 * Subtlety here: if ptrace pokes something larger than 309 * 2^32-1 into orig_ax, this truncates it. This may or 310 * may not be necessary, but it matches the old asm 311 * behavior. 312 */ 313 nr = syscall_trace_enter(regs); 314 } 315 316 if (likely(nr < IA32_NR_syscalls)) { 317 /* 318 * It's possible that a 32-bit syscall implementation 319 * takes a 64-bit parameter but nonetheless assumes that 320 * the high bits are zero. Make sure we zero-extend all 321 * of the args. 322 */ 323 regs->ax = ia32_sys_call_table[nr]( 324 (unsigned int)regs->bx, (unsigned int)regs->cx, 325 (unsigned int)regs->dx, (unsigned int)regs->si, 326 (unsigned int)regs->di, (unsigned int)regs->bp); 327 } 328 329 syscall_return_slowpath(regs); 330 } 331 332 /* Handles int $0x80 */ 333 __visible void do_int80_syscall_32(struct pt_regs *regs) 334 { 335 enter_from_user_mode(); 336 local_irq_enable(); 337 do_syscall_32_irqs_on(regs); 338 } 339 340 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */ 341 __visible long do_fast_syscall_32(struct pt_regs *regs) 342 { 343 /* 344 * Called using the internal vDSO SYSENTER/SYSCALL32 calling 345 * convention. Adjust regs so it looks like we entered using int80. 346 */ 347 348 unsigned long landing_pad = (unsigned long)current->mm->context.vdso + 349 vdso_image_32.sym_int80_landing_pad; 350 351 /* 352 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward 353 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction. 354 * Fix it up. 355 */ 356 regs->ip = landing_pad; 357 358 enter_from_user_mode(); 359 360 local_irq_enable(); 361 362 /* Fetch EBP from where the vDSO stashed it. */ 363 if ( 364 #ifdef CONFIG_X86_64 365 /* 366 * Micro-optimization: the pointer we're following is explicitly 367 * 32 bits, so it can't be out of range. 368 */ 369 __get_user(*(u32 *)®s->bp, 370 (u32 __user __force *)(unsigned long)(u32)regs->sp) 371 #else 372 get_user(*(u32 *)®s->bp, 373 (u32 __user __force *)(unsigned long)(u32)regs->sp) 374 #endif 375 ) { 376 377 /* User code screwed up. */ 378 local_irq_disable(); 379 regs->ax = -EFAULT; 380 prepare_exit_to_usermode(regs); 381 return 0; /* Keep it simple: use IRET. */ 382 } 383 384 /* Now this is just like a normal syscall. */ 385 do_syscall_32_irqs_on(regs); 386 387 #ifdef CONFIG_X86_64 388 /* 389 * Opportunistic SYSRETL: if possible, try to return using SYSRETL. 390 * SYSRETL is available on all 64-bit CPUs, so we don't need to 391 * bother with SYSEXIT. 392 * 393 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, 394 * because the ECX fixup above will ensure that this is essentially 395 * never the case. 396 */ 397 return regs->cs == __USER32_CS && regs->ss == __USER_DS && 398 regs->ip == landing_pad && 399 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0; 400 #else 401 /* 402 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT. 403 * 404 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, 405 * because the ECX fixup above will ensure that this is essentially 406 * never the case. 407 * 408 * We don't allow syscalls at all from VM86 mode, but we still 409 * need to check VM, because we might be returning from sys_vm86. 410 */ 411 return static_cpu_has(X86_FEATURE_SEP) && 412 regs->cs == __USER_CS && regs->ss == __USER_DS && 413 regs->ip == landing_pad && 414 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0; 415 #endif 416 } 417 #endif 418