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 #include <linux/livepatch.h> 26 27 #include <asm/desc.h> 28 #include <asm/traps.h> 29 #include <asm/vdso.h> 30 #include <linux/uaccess.h> 31 #include <asm/cpufeature.h> 32 33 #define CREATE_TRACE_POINTS 34 #include <trace/events/syscalls.h> 35 36 #ifdef CONFIG_CONTEXT_TRACKING 37 /* Called on entry from user mode with IRQs off. */ 38 __visible inline void enter_from_user_mode(void) 39 { 40 CT_WARN_ON(ct_state() != CONTEXT_USER); 41 user_exit_irqoff(); 42 } 43 #else 44 static inline void enter_from_user_mode(void) {} 45 #endif 46 47 static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) 48 { 49 #ifdef CONFIG_X86_64 50 if (arch == AUDIT_ARCH_X86_64) { 51 audit_syscall_entry(regs->orig_ax, regs->di, 52 regs->si, regs->dx, regs->r10); 53 } else 54 #endif 55 { 56 audit_syscall_entry(regs->orig_ax, regs->bx, 57 regs->cx, regs->dx, regs->si); 58 } 59 } 60 61 /* 62 * Returns the syscall nr to run (which should match regs->orig_ax) or -1 63 * to skip the syscall. 64 */ 65 static long syscall_trace_enter(struct pt_regs *regs) 66 { 67 u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64; 68 69 struct thread_info *ti = current_thread_info(); 70 unsigned long ret = 0; 71 bool emulated = false; 72 u32 work; 73 74 if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) 75 BUG_ON(regs != task_pt_regs(current)); 76 77 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY; 78 79 if (unlikely(work & _TIF_SYSCALL_EMU)) 80 emulated = true; 81 82 if ((emulated || (work & _TIF_SYSCALL_TRACE)) && 83 tracehook_report_syscall_entry(regs)) 84 return -1L; 85 86 if (emulated) 87 return -1L; 88 89 #ifdef CONFIG_SECCOMP 90 /* 91 * Do seccomp after ptrace, to catch any tracer changes. 92 */ 93 if (work & _TIF_SECCOMP) { 94 struct seccomp_data sd; 95 96 sd.arch = arch; 97 sd.nr = regs->orig_ax; 98 sd.instruction_pointer = regs->ip; 99 #ifdef CONFIG_X86_64 100 if (arch == AUDIT_ARCH_X86_64) { 101 sd.args[0] = regs->di; 102 sd.args[1] = regs->si; 103 sd.args[2] = regs->dx; 104 sd.args[3] = regs->r10; 105 sd.args[4] = regs->r8; 106 sd.args[5] = regs->r9; 107 } else 108 #endif 109 { 110 sd.args[0] = regs->bx; 111 sd.args[1] = regs->cx; 112 sd.args[2] = regs->dx; 113 sd.args[3] = regs->si; 114 sd.args[4] = regs->di; 115 sd.args[5] = regs->bp; 116 } 117 118 ret = __secure_computing(&sd); 119 if (ret == -1) 120 return ret; 121 } 122 #endif 123 124 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT))) 125 trace_sys_enter(regs, regs->orig_ax); 126 127 do_audit_syscall_entry(regs, arch); 128 129 return ret ?: regs->orig_ax; 130 } 131 132 #define EXIT_TO_USERMODE_LOOP_FLAGS \ 133 (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ 134 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING) 135 136 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) 137 { 138 /* 139 * In order to return to user mode, we need to have IRQs off with 140 * none of EXIT_TO_USERMODE_LOOP_FLAGS 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 if (cached_flags & _TIF_PATCH_PENDING) 168 klp_update_patch_state(current); 169 170 /* Disable IRQs and retry */ 171 local_irq_disable(); 172 173 cached_flags = READ_ONCE(current_thread_info()->flags); 174 175 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 176 break; 177 } 178 } 179 180 /* Called with IRQs disabled. */ 181 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) 182 { 183 struct thread_info *ti = current_thread_info(); 184 u32 cached_flags; 185 186 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled())) 187 local_irq_disable(); 188 189 lockdep_sys_exit(); 190 191 cached_flags = READ_ONCE(ti->flags); 192 193 if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 194 exit_to_usermode_loop(regs, cached_flags); 195 196 #ifdef CONFIG_COMPAT 197 /* 198 * Compat syscalls set TS_COMPAT. Make sure we clear it before 199 * returning to user mode. We need to clear it *after* signal 200 * handling, because syscall restart has a fixup for compat 201 * syscalls. The fixup is exercised by the ptrace_syscall_32 202 * selftest. 203 * 204 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer 205 * special case only applies after poking regs and before the 206 * very next return to user mode. 207 */ 208 current->thread.status &= ~(TS_COMPAT|TS_I386_REGS_POKED); 209 #endif 210 211 user_enter_irqoff(); 212 } 213 214 #define SYSCALL_EXIT_WORK_FLAGS \ 215 (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \ 216 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT) 217 218 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags) 219 { 220 bool step; 221 222 audit_syscall_exit(regs); 223 224 if (cached_flags & _TIF_SYSCALL_TRACEPOINT) 225 trace_sys_exit(regs, regs->ax); 226 227 /* 228 * If TIF_SYSCALL_EMU is set, we only get here because of 229 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP). 230 * We already reported this syscall instruction in 231 * syscall_trace_enter(). 232 */ 233 step = unlikely( 234 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)) 235 == _TIF_SINGLESTEP); 236 if (step || cached_flags & _TIF_SYSCALL_TRACE) 237 tracehook_report_syscall_exit(regs, step); 238 } 239 240 /* 241 * Called with IRQs on and fully valid regs. Returns with IRQs off in a 242 * state such that we can immediately switch to user mode. 243 */ 244 __visible inline void syscall_return_slowpath(struct pt_regs *regs) 245 { 246 struct thread_info *ti = current_thread_info(); 247 u32 cached_flags = READ_ONCE(ti->flags); 248 249 CT_WARN_ON(ct_state() != CONTEXT_KERNEL); 250 251 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && 252 WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax)) 253 local_irq_enable(); 254 255 /* 256 * First do one-time work. If these work items are enabled, we 257 * want to run them exactly once per syscall exit with IRQs on. 258 */ 259 if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS)) 260 syscall_slow_exit_work(regs, cached_flags); 261 262 local_irq_disable(); 263 prepare_exit_to_usermode(regs); 264 } 265 266 #ifdef CONFIG_X86_64 267 __visible void do_syscall_64(struct pt_regs *regs) 268 { 269 struct thread_info *ti = current_thread_info(); 270 unsigned long nr = regs->orig_ax; 271 272 enter_from_user_mode(); 273 local_irq_enable(); 274 275 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) 276 nr = syscall_trace_enter(regs); 277 278 /* 279 * NB: Native and x32 syscalls are dispatched from the same 280 * table. The only functional difference is the x32 bit in 281 * regs->orig_ax, which changes the behavior of some syscalls. 282 */ 283 if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) { 284 regs->ax = sys_call_table[nr & __SYSCALL_MASK]( 285 regs->di, regs->si, regs->dx, 286 regs->r10, regs->r8, regs->r9); 287 } 288 289 syscall_return_slowpath(regs); 290 } 291 #endif 292 293 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) 294 /* 295 * Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does 296 * all entry and exit work and returns with IRQs off. This function is 297 * extremely hot in workloads that use it, and it's usually called from 298 * do_fast_syscall_32, so forcibly inline it to improve performance. 299 */ 300 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) 301 { 302 struct thread_info *ti = current_thread_info(); 303 unsigned int nr = (unsigned int)regs->orig_ax; 304 305 #ifdef CONFIG_IA32_EMULATION 306 current->thread.status |= TS_COMPAT; 307 #endif 308 309 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) { 310 /* 311 * Subtlety here: if ptrace pokes something larger than 312 * 2^32-1 into orig_ax, this truncates it. This may or 313 * may not be necessary, but it matches the old asm 314 * behavior. 315 */ 316 nr = syscall_trace_enter(regs); 317 } 318 319 if (likely(nr < IA32_NR_syscalls)) { 320 /* 321 * It's possible that a 32-bit syscall implementation 322 * takes a 64-bit parameter but nonetheless assumes that 323 * the high bits are zero. Make sure we zero-extend all 324 * of the args. 325 */ 326 regs->ax = ia32_sys_call_table[nr]( 327 (unsigned int)regs->bx, (unsigned int)regs->cx, 328 (unsigned int)regs->dx, (unsigned int)regs->si, 329 (unsigned int)regs->di, (unsigned int)regs->bp); 330 } 331 332 syscall_return_slowpath(regs); 333 } 334 335 /* Handles int $0x80 */ 336 __visible void do_int80_syscall_32(struct pt_regs *regs) 337 { 338 enter_from_user_mode(); 339 local_irq_enable(); 340 do_syscall_32_irqs_on(regs); 341 } 342 343 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */ 344 __visible long do_fast_syscall_32(struct pt_regs *regs) 345 { 346 /* 347 * Called using the internal vDSO SYSENTER/SYSCALL32 calling 348 * convention. Adjust regs so it looks like we entered using int80. 349 */ 350 351 unsigned long landing_pad = (unsigned long)current->mm->context.vdso + 352 vdso_image_32.sym_int80_landing_pad; 353 354 /* 355 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward 356 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction. 357 * Fix it up. 358 */ 359 regs->ip = landing_pad; 360 361 enter_from_user_mode(); 362 363 local_irq_enable(); 364 365 /* Fetch EBP from where the vDSO stashed it. */ 366 if ( 367 #ifdef CONFIG_X86_64 368 /* 369 * Micro-optimization: the pointer we're following is explicitly 370 * 32 bits, so it can't be out of range. 371 */ 372 __get_user(*(u32 *)®s->bp, 373 (u32 __user __force *)(unsigned long)(u32)regs->sp) 374 #else 375 get_user(*(u32 *)®s->bp, 376 (u32 __user __force *)(unsigned long)(u32)regs->sp) 377 #endif 378 ) { 379 380 /* User code screwed up. */ 381 local_irq_disable(); 382 regs->ax = -EFAULT; 383 prepare_exit_to_usermode(regs); 384 return 0; /* Keep it simple: use IRET. */ 385 } 386 387 /* Now this is just like a normal syscall. */ 388 do_syscall_32_irqs_on(regs); 389 390 #ifdef CONFIG_X86_64 391 /* 392 * Opportunistic SYSRETL: if possible, try to return using SYSRETL. 393 * SYSRETL is available on all 64-bit CPUs, so we don't need to 394 * bother with SYSEXIT. 395 * 396 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, 397 * because the ECX fixup above will ensure that this is essentially 398 * never the case. 399 */ 400 return regs->cs == __USER32_CS && regs->ss == __USER_DS && 401 regs->ip == landing_pad && 402 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0; 403 #else 404 /* 405 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT. 406 * 407 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, 408 * because the ECX fixup above will ensure that this is essentially 409 * never the case. 410 * 411 * We don't allow syscalls at all from VM86 mode, but we still 412 * need to check VM, because we might be returning from sys_vm86. 413 */ 414 return static_cpu_has(X86_FEATURE_SEP) && 415 regs->cs == __USER_CS && regs->ss == __USER_DS && 416 regs->ip == landing_pad && 417 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0; 418 #endif 419 } 420 #endif 421