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 static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs) 35 { 36 unsigned long top_of_stack = 37 (unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING; 38 return (struct thread_info *)(top_of_stack - THREAD_SIZE); 39 } 40 41 #ifdef CONFIG_CONTEXT_TRACKING 42 /* Called on entry from user mode with IRQs off. */ 43 __visible void enter_from_user_mode(void) 44 { 45 CT_WARN_ON(ct_state() != CONTEXT_USER); 46 user_exit(); 47 } 48 #else 49 static inline void enter_from_user_mode(void) {} 50 #endif 51 52 static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) 53 { 54 #ifdef CONFIG_X86_64 55 if (arch == AUDIT_ARCH_X86_64) { 56 audit_syscall_entry(regs->orig_ax, regs->di, 57 regs->si, regs->dx, regs->r10); 58 } else 59 #endif 60 { 61 audit_syscall_entry(regs->orig_ax, regs->bx, 62 regs->cx, regs->dx, regs->si); 63 } 64 } 65 66 /* 67 * Returns the syscall nr to run (which should match regs->orig_ax) or -1 68 * to skip the syscall. 69 */ 70 static long syscall_trace_enter(struct pt_regs *regs) 71 { 72 u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64; 73 74 struct thread_info *ti = pt_regs_to_thread_info(regs); 75 unsigned long ret = 0; 76 bool emulated = false; 77 u32 work; 78 79 if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) 80 BUG_ON(regs != task_pt_regs(current)); 81 82 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY; 83 84 if (unlikely(work & _TIF_SYSCALL_EMU)) 85 emulated = true; 86 87 if ((emulated || (work & _TIF_SYSCALL_TRACE)) && 88 tracehook_report_syscall_entry(regs)) 89 return -1L; 90 91 if (emulated) 92 return -1L; 93 94 #ifdef CONFIG_SECCOMP 95 /* 96 * Do seccomp after ptrace, to catch any tracer changes. 97 */ 98 if (work & _TIF_SECCOMP) { 99 struct seccomp_data sd; 100 101 sd.arch = arch; 102 sd.nr = regs->orig_ax; 103 sd.instruction_pointer = regs->ip; 104 #ifdef CONFIG_X86_64 105 if (arch == AUDIT_ARCH_X86_64) { 106 sd.args[0] = regs->di; 107 sd.args[1] = regs->si; 108 sd.args[2] = regs->dx; 109 sd.args[3] = regs->r10; 110 sd.args[4] = regs->r8; 111 sd.args[5] = regs->r9; 112 } else 113 #endif 114 { 115 sd.args[0] = regs->bx; 116 sd.args[1] = regs->cx; 117 sd.args[2] = regs->dx; 118 sd.args[3] = regs->si; 119 sd.args[4] = regs->di; 120 sd.args[5] = regs->bp; 121 } 122 123 ret = __secure_computing(&sd); 124 if (ret == -1) 125 return ret; 126 } 127 #endif 128 129 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT))) 130 trace_sys_enter(regs, regs->orig_ax); 131 132 do_audit_syscall_entry(regs, arch); 133 134 return ret ?: regs->orig_ax; 135 } 136 137 #define EXIT_TO_USERMODE_LOOP_FLAGS \ 138 (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ 139 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY) 140 141 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) 142 { 143 /* 144 * In order to return to user mode, we need to have IRQs off with 145 * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY, 146 * _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags 147 * can be set at any time on preemptable kernels if we have IRQs on, 148 * so we need to loop. Disabling preemption wouldn't help: doing the 149 * work to clear some of the flags can sleep. 150 */ 151 while (true) { 152 /* We have work to do. */ 153 local_irq_enable(); 154 155 if (cached_flags & _TIF_NEED_RESCHED) 156 schedule(); 157 158 if (cached_flags & _TIF_UPROBE) 159 uprobe_notify_resume(regs); 160 161 /* deal with pending signal delivery */ 162 if (cached_flags & _TIF_SIGPENDING) 163 do_signal(regs); 164 165 if (cached_flags & _TIF_NOTIFY_RESUME) { 166 clear_thread_flag(TIF_NOTIFY_RESUME); 167 tracehook_notify_resume(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(pt_regs_to_thread_info(regs)->flags); 177 178 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 179 break; 180 181 } 182 } 183 184 /* Called with IRQs disabled. */ 185 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) 186 { 187 struct thread_info *ti = pt_regs_to_thread_info(regs); 188 u32 cached_flags; 189 190 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled())) 191 local_irq_disable(); 192 193 lockdep_sys_exit(); 194 195 cached_flags = READ_ONCE(ti->flags); 196 197 if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 198 exit_to_usermode_loop(regs, cached_flags); 199 200 #ifdef CONFIG_COMPAT 201 /* 202 * Compat syscalls set TS_COMPAT. Make sure we clear it before 203 * returning to user mode. We need to clear it *after* signal 204 * handling, because syscall restart has a fixup for compat 205 * syscalls. The fixup is exercised by the ptrace_syscall_32 206 * selftest. 207 */ 208 ti->status &= ~TS_COMPAT; 209 #endif 210 211 user_enter(); 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 = pt_regs_to_thread_info(regs); 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 = pt_regs_to_thread_info(regs); 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 = pt_regs_to_thread_info(regs); 303 unsigned int nr = (unsigned int)regs->orig_ax; 304 305 #ifdef CONFIG_IA32_EMULATION 306 ti->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