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/nospec.h> 25 #include <linux/uprobes.h> 26 #include <linux/livepatch.h> 27 #include <linux/syscalls.h> 28 29 #include <asm/desc.h> 30 #include <asm/traps.h> 31 #include <asm/vdso.h> 32 #include <linux/uaccess.h> 33 #include <asm/cpufeature.h> 34 35 #define CREATE_TRACE_POINTS 36 #include <trace/events/syscalls.h> 37 38 #ifdef CONFIG_CONTEXT_TRACKING 39 /* Called on entry from user mode with IRQs off. */ 40 __visible inline void enter_from_user_mode(void) 41 { 42 CT_WARN_ON(ct_state() != CONTEXT_USER); 43 user_exit_irqoff(); 44 } 45 #else 46 static inline void enter_from_user_mode(void) {} 47 #endif 48 49 static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) 50 { 51 #ifdef CONFIG_X86_64 52 if (arch == AUDIT_ARCH_X86_64) { 53 audit_syscall_entry(regs->orig_ax, regs->di, 54 regs->si, regs->dx, regs->r10); 55 } else 56 #endif 57 { 58 audit_syscall_entry(regs->orig_ax, regs->bx, 59 regs->cx, regs->dx, regs->si); 60 } 61 } 62 63 /* 64 * Returns the syscall nr to run (which should match regs->orig_ax) or -1 65 * to skip the syscall. 66 */ 67 static long syscall_trace_enter(struct pt_regs *regs) 68 { 69 u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64; 70 71 struct thread_info *ti = current_thread_info(); 72 unsigned long ret = 0; 73 bool emulated = false; 74 u32 work; 75 76 if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) 77 BUG_ON(regs != task_pt_regs(current)); 78 79 work = READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY; 80 81 if (unlikely(work & _TIF_SYSCALL_EMU)) 82 emulated = true; 83 84 if ((emulated || (work & _TIF_SYSCALL_TRACE)) && 85 tracehook_report_syscall_entry(regs)) 86 return -1L; 87 88 if (emulated) 89 return -1L; 90 91 #ifdef CONFIG_SECCOMP 92 /* 93 * Do seccomp after ptrace, to catch any tracer changes. 94 */ 95 if (work & _TIF_SECCOMP) { 96 struct seccomp_data sd; 97 98 sd.arch = arch; 99 sd.nr = regs->orig_ax; 100 sd.instruction_pointer = regs->ip; 101 #ifdef CONFIG_X86_64 102 if (arch == AUDIT_ARCH_X86_64) { 103 sd.args[0] = regs->di; 104 sd.args[1] = regs->si; 105 sd.args[2] = regs->dx; 106 sd.args[3] = regs->r10; 107 sd.args[4] = regs->r8; 108 sd.args[5] = regs->r9; 109 } else 110 #endif 111 { 112 sd.args[0] = regs->bx; 113 sd.args[1] = regs->cx; 114 sd.args[2] = regs->dx; 115 sd.args[3] = regs->si; 116 sd.args[4] = regs->di; 117 sd.args[5] = regs->bp; 118 } 119 120 ret = __secure_computing(&sd); 121 if (ret == -1) 122 return ret; 123 } 124 #endif 125 126 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT))) 127 trace_sys_enter(regs, regs->orig_ax); 128 129 do_audit_syscall_entry(regs, arch); 130 131 return ret ?: regs->orig_ax; 132 } 133 134 #define EXIT_TO_USERMODE_LOOP_FLAGS \ 135 (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ 136 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING) 137 138 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) 139 { 140 /* 141 * In order to return to user mode, we need to have IRQs off with 142 * none of EXIT_TO_USERMODE_LOOP_FLAGS set. Several of these flags 143 * can be set at any time on preemptible kernels if we have IRQs on, 144 * so we need to loop. Disabling preemption wouldn't help: doing the 145 * work to clear some of the flags can sleep. 146 */ 147 while (true) { 148 /* We have work to do. */ 149 local_irq_enable(); 150 151 if (cached_flags & _TIF_NEED_RESCHED) 152 schedule(); 153 154 if (cached_flags & _TIF_UPROBE) 155 uprobe_notify_resume(regs); 156 157 if (cached_flags & _TIF_PATCH_PENDING) 158 klp_update_patch_state(current); 159 160 /* deal with pending signal delivery */ 161 if (cached_flags & _TIF_SIGPENDING) 162 do_signal(regs); 163 164 if (cached_flags & _TIF_NOTIFY_RESUME) { 165 clear_thread_flag(TIF_NOTIFY_RESUME); 166 tracehook_notify_resume(regs); 167 rseq_handle_notify_resume(NULL, regs); 168 } 169 170 if (cached_flags & _TIF_USER_RETURN_NOTIFY) 171 fire_user_return_notifiers(); 172 173 /* Disable IRQs and retry */ 174 local_irq_disable(); 175 176 cached_flags = READ_ONCE(current_thread_info()->flags); 177 178 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 179 break; 180 } 181 } 182 183 /* Called with IRQs disabled. */ 184 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) 185 { 186 struct thread_info *ti = current_thread_info(); 187 u32 cached_flags; 188 189 addr_limit_user_check(); 190 191 lockdep_assert_irqs_disabled(); 192 lockdep_sys_exit(); 193 194 cached_flags = READ_ONCE(ti->flags); 195 196 if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 197 exit_to_usermode_loop(regs, cached_flags); 198 199 #ifdef CONFIG_COMPAT 200 /* 201 * Compat syscalls set TS_COMPAT. Make sure we clear it before 202 * returning to user mode. We need to clear it *after* signal 203 * handling, because syscall restart has a fixup for compat 204 * syscalls. The fixup is exercised by the ptrace_syscall_32 205 * selftest. 206 * 207 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer 208 * special case only applies after poking regs and before the 209 * very next return to user mode. 210 */ 211 ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED); 212 #endif 213 214 user_enter_irqoff(); 215 } 216 217 #define SYSCALL_EXIT_WORK_FLAGS \ 218 (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \ 219 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT) 220 221 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags) 222 { 223 bool step; 224 225 audit_syscall_exit(regs); 226 227 if (cached_flags & _TIF_SYSCALL_TRACEPOINT) 228 trace_sys_exit(regs, regs->ax); 229 230 /* 231 * If TIF_SYSCALL_EMU is set, we only get here because of 232 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP). 233 * We already reported this syscall instruction in 234 * syscall_trace_enter(). 235 */ 236 step = unlikely( 237 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)) 238 == _TIF_SINGLESTEP); 239 if (step || cached_flags & _TIF_SYSCALL_TRACE) 240 tracehook_report_syscall_exit(regs, step); 241 } 242 243 /* 244 * Called with IRQs on and fully valid regs. Returns with IRQs off in a 245 * state such that we can immediately switch to user mode. 246 */ 247 __visible inline void syscall_return_slowpath(struct pt_regs *regs) 248 { 249 struct thread_info *ti = current_thread_info(); 250 u32 cached_flags = READ_ONCE(ti->flags); 251 252 CT_WARN_ON(ct_state() != CONTEXT_KERNEL); 253 254 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && 255 WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax)) 256 local_irq_enable(); 257 258 rseq_syscall(regs); 259 260 /* 261 * First do one-time work. If these work items are enabled, we 262 * want to run them exactly once per syscall exit with IRQs on. 263 */ 264 if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS)) 265 syscall_slow_exit_work(regs, cached_flags); 266 267 local_irq_disable(); 268 prepare_exit_to_usermode(regs); 269 } 270 271 #ifdef CONFIG_X86_64 272 __visible void do_syscall_64(unsigned long nr, struct pt_regs *regs) 273 { 274 struct thread_info *ti; 275 276 enter_from_user_mode(); 277 local_irq_enable(); 278 ti = current_thread_info(); 279 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) 280 nr = syscall_trace_enter(regs); 281 282 /* 283 * NB: Native and x32 syscalls are dispatched from the same 284 * table. The only functional difference is the x32 bit in 285 * regs->orig_ax, which changes the behavior of some syscalls. 286 */ 287 nr &= __SYSCALL_MASK; 288 if (likely(nr < NR_syscalls)) { 289 nr = array_index_nospec(nr, NR_syscalls); 290 regs->ax = sys_call_table[nr](regs); 291 } 292 293 syscall_return_slowpath(regs); 294 } 295 #endif 296 297 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) 298 /* 299 * Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does 300 * all entry and exit work and returns with IRQs off. This function is 301 * extremely hot in workloads that use it, and it's usually called from 302 * do_fast_syscall_32, so forcibly inline it to improve performance. 303 */ 304 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) 305 { 306 struct thread_info *ti = current_thread_info(); 307 unsigned int nr = (unsigned int)regs->orig_ax; 308 309 #ifdef CONFIG_IA32_EMULATION 310 ti->status |= TS_COMPAT; 311 #endif 312 313 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) { 314 /* 315 * Subtlety here: if ptrace pokes something larger than 316 * 2^32-1 into orig_ax, this truncates it. This may or 317 * may not be necessary, but it matches the old asm 318 * behavior. 319 */ 320 nr = syscall_trace_enter(regs); 321 } 322 323 if (likely(nr < IA32_NR_syscalls)) { 324 nr = array_index_nospec(nr, IA32_NR_syscalls); 325 #ifdef CONFIG_IA32_EMULATION 326 regs->ax = ia32_sys_call_table[nr](regs); 327 #else 328 /* 329 * It's possible that a 32-bit syscall implementation 330 * takes a 64-bit parameter but nonetheless assumes that 331 * the high bits are zero. Make sure we zero-extend all 332 * of the args. 333 */ 334 regs->ax = ia32_sys_call_table[nr]( 335 (unsigned int)regs->bx, (unsigned int)regs->cx, 336 (unsigned int)regs->dx, (unsigned int)regs->si, 337 (unsigned int)regs->di, (unsigned int)regs->bp); 338 #endif /* CONFIG_IA32_EMULATION */ 339 } 340 341 syscall_return_slowpath(regs); 342 } 343 344 /* Handles int $0x80 */ 345 __visible void do_int80_syscall_32(struct pt_regs *regs) 346 { 347 enter_from_user_mode(); 348 local_irq_enable(); 349 do_syscall_32_irqs_on(regs); 350 } 351 352 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */ 353 __visible long do_fast_syscall_32(struct pt_regs *regs) 354 { 355 /* 356 * Called using the internal vDSO SYSENTER/SYSCALL32 calling 357 * convention. Adjust regs so it looks like we entered using int80. 358 */ 359 360 unsigned long landing_pad = (unsigned long)current->mm->context.vdso + 361 vdso_image_32.sym_int80_landing_pad; 362 363 /* 364 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward 365 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction. 366 * Fix it up. 367 */ 368 regs->ip = landing_pad; 369 370 enter_from_user_mode(); 371 372 local_irq_enable(); 373 374 /* Fetch EBP from where the vDSO stashed it. */ 375 if ( 376 #ifdef CONFIG_X86_64 377 /* 378 * Micro-optimization: the pointer we're following is explicitly 379 * 32 bits, so it can't be out of range. 380 */ 381 __get_user(*(u32 *)®s->bp, 382 (u32 __user __force *)(unsigned long)(u32)regs->sp) 383 #else 384 get_user(*(u32 *)®s->bp, 385 (u32 __user __force *)(unsigned long)(u32)regs->sp) 386 #endif 387 ) { 388 389 /* User code screwed up. */ 390 local_irq_disable(); 391 regs->ax = -EFAULT; 392 prepare_exit_to_usermode(regs); 393 return 0; /* Keep it simple: use IRET. */ 394 } 395 396 /* Now this is just like a normal syscall. */ 397 do_syscall_32_irqs_on(regs); 398 399 #ifdef CONFIG_X86_64 400 /* 401 * Opportunistic SYSRETL: if possible, try to return using SYSRETL. 402 * SYSRETL is available on all 64-bit CPUs, so we don't need to 403 * bother with SYSEXIT. 404 * 405 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, 406 * because the ECX fixup above will ensure that this is essentially 407 * never the case. 408 */ 409 return regs->cs == __USER32_CS && regs->ss == __USER_DS && 410 regs->ip == landing_pad && 411 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0; 412 #else 413 /* 414 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT. 415 * 416 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, 417 * because the ECX fixup above will ensure that this is essentially 418 * never the case. 419 * 420 * We don't allow syscalls at all from VM86 mode, but we still 421 * need to check VM, because we might be returning from sys_vm86. 422 */ 423 return static_cpu_has(X86_FEATURE_SEP) && 424 regs->cs == __USER_CS && regs->ss == __USER_DS && 425 regs->ip == landing_pad && 426 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0; 427 #endif 428 } 429 #endif 430