1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Copyright (C) 1991, 1992 Linus Torvalds 4 * Copyright (C) 2000, 2001, 2002 Andi Kleen SuSE Labs 5 * 6 * 1997-11-28 Modified for POSIX.1b signals by Richard Henderson 7 * 2000-06-20 Pentium III FXSR, SSE support by Gareth Hughes 8 * 2000-2002 x86-64 support by Andi Kleen 9 */ 10 11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 12 13 #include <linux/sched.h> 14 #include <linux/sched/task_stack.h> 15 #include <linux/mm.h> 16 #include <linux/smp.h> 17 #include <linux/kernel.h> 18 #include <linux/kstrtox.h> 19 #include <linux/errno.h> 20 #include <linux/wait.h> 21 #include <linux/unistd.h> 22 #include <linux/stddef.h> 23 #include <linux/personality.h> 24 #include <linux/uaccess.h> 25 #include <linux/user-return-notifier.h> 26 #include <linux/uprobes.h> 27 #include <linux/context_tracking.h> 28 #include <linux/entry-common.h> 29 #include <linux/syscalls.h> 30 #include <linux/rseq.h> 31 32 #include <asm/processor.h> 33 #include <asm/ucontext.h> 34 #include <asm/fpu/signal.h> 35 #include <asm/fpu/xstate.h> 36 #include <asm/vdso.h> 37 #include <asm/mce.h> 38 #include <asm/sighandling.h> 39 #include <asm/vm86.h> 40 41 #include <asm/syscall.h> 42 #include <asm/sigframe.h> 43 #include <asm/signal.h> 44 #include <asm/shstk.h> 45 46 static inline int is_ia32_compat_frame(struct ksignal *ksig) 47 { 48 return IS_ENABLED(CONFIG_IA32_EMULATION) && 49 ksig->ka.sa.sa_flags & SA_IA32_ABI; 50 } 51 52 static inline int is_ia32_frame(struct ksignal *ksig) 53 { 54 return IS_ENABLED(CONFIG_X86_32) || is_ia32_compat_frame(ksig); 55 } 56 57 static inline int is_x32_frame(struct ksignal *ksig) 58 { 59 return IS_ENABLED(CONFIG_X86_X32_ABI) && 60 ksig->ka.sa.sa_flags & SA_X32_ABI; 61 } 62 63 /* 64 * Enable all pkeys temporarily, so as to ensure that both the current 65 * execution stack as well as the alternate signal stack are writeable. 66 * The application can use any of the available pkeys to protect the 67 * alternate signal stack, and we don't know which one it is, so enable 68 * all. The PKRU register will be reset to init_pkru later in the flow, 69 * in fpu__clear_user_states(), and it is the application's responsibility 70 * to enable the appropriate pkey as the first step in the signal handler 71 * so that the handler does not segfault. 72 */ 73 static inline u32 sig_prepare_pkru(void) 74 { 75 u32 orig_pkru = read_pkru(); 76 77 write_pkru(0); 78 return orig_pkru; 79 } 80 81 /* 82 * Set up a signal frame. 83 */ 84 85 /* x86 ABI requires 16-byte alignment */ 86 #define FRAME_ALIGNMENT 16UL 87 88 #define MAX_FRAME_PADDING (FRAME_ALIGNMENT - 1) 89 90 /* 91 * Determine which stack to use.. 92 */ 93 void __user * 94 get_sigframe(struct ksignal *ksig, struct pt_regs *regs, size_t frame_size, 95 void __user **fpstate) 96 { 97 struct k_sigaction *ka = &ksig->ka; 98 int ia32_frame = is_ia32_frame(ksig); 99 /* Default to using normal stack */ 100 bool nested_altstack = on_sig_stack(regs->sp); 101 bool entering_altstack = false; 102 unsigned long math_size = 0; 103 unsigned long sp = regs->sp; 104 unsigned long buf_fx = 0; 105 u32 pkru; 106 107 /* redzone */ 108 if (!ia32_frame) 109 sp -= 128; 110 111 /* This is the X/Open sanctioned signal stack switching. */ 112 if (ka->sa.sa_flags & SA_ONSTACK) { 113 /* 114 * This checks nested_altstack via sas_ss_flags(). Sensible 115 * programs use SS_AUTODISARM, which disables that check, and 116 * programs that don't use SS_AUTODISARM get compatible. 117 */ 118 if (sas_ss_flags(sp) == 0) { 119 sp = current->sas_ss_sp + current->sas_ss_size; 120 entering_altstack = true; 121 } 122 } else if (ia32_frame && 123 !nested_altstack && 124 regs->ss != __USER_DS && 125 !(ka->sa.sa_flags & SA_RESTORER) && 126 ka->sa.sa_restorer) { 127 /* This is the legacy signal stack switching. */ 128 sp = (unsigned long) ka->sa.sa_restorer; 129 entering_altstack = true; 130 } 131 132 sp = fpu__alloc_mathframe(sp, ia32_frame, &buf_fx, &math_size); 133 *fpstate = (void __user *)sp; 134 135 sp -= frame_size; 136 137 if (ia32_frame) 138 /* 139 * Align the stack pointer according to the i386 ABI, 140 * i.e. so that on function entry ((sp + 4) & 15) == 0. 141 */ 142 sp = ((sp + 4) & -FRAME_ALIGNMENT) - 4; 143 else 144 sp = round_down(sp, FRAME_ALIGNMENT) - 8; 145 146 /* 147 * If we are on the alternate signal stack and would overflow it, don't. 148 * Return an always-bogus address instead so we will die with SIGSEGV. 149 */ 150 if (unlikely((nested_altstack || entering_altstack) && 151 !__on_sig_stack(sp))) { 152 153 if (show_unhandled_signals && printk_ratelimit()) 154 pr_info("%s[%d] overflowed sigaltstack\n", 155 current->comm, task_pid_nr(current)); 156 157 return (void __user *)-1L; 158 } 159 160 /* Update PKRU to enable access to the alternate signal stack. */ 161 pkru = sig_prepare_pkru(); 162 /* save i387 and extended state */ 163 if (!copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size, pkru)) { 164 /* 165 * Restore PKRU to the original, user-defined value; disable 166 * extra pkeys enabled for the alternate signal stack, if any. 167 */ 168 write_pkru(pkru); 169 return (void __user *)-1L; 170 } 171 172 return (void __user *)sp; 173 } 174 175 /* 176 * There are four different struct types for signal frame: sigframe_ia32, 177 * rt_sigframe_ia32, rt_sigframe_x32, and rt_sigframe. Use the worst case 178 * -- the largest size. It means the size for 64-bit apps is a bit more 179 * than needed, but this keeps the code simple. 180 */ 181 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) 182 # define MAX_FRAME_SIGINFO_UCTXT_SIZE sizeof(struct sigframe_ia32) 183 #else 184 # define MAX_FRAME_SIGINFO_UCTXT_SIZE sizeof(struct rt_sigframe) 185 #endif 186 187 /* 188 * The FP state frame contains an XSAVE buffer which must be 64-byte aligned. 189 * If a signal frame starts at an unaligned address, extra space is required. 190 * This is the max alignment padding, conservatively. 191 */ 192 #define MAX_XSAVE_PADDING 63UL 193 194 /* 195 * The frame data is composed of the following areas and laid out as: 196 * 197 * ------------------------- 198 * | alignment padding | 199 * ------------------------- 200 * | (f)xsave frame | 201 * ------------------------- 202 * | fsave header | 203 * ------------------------- 204 * | alignment padding | 205 * ------------------------- 206 * | siginfo + ucontext | 207 * ------------------------- 208 */ 209 210 /* max_frame_size tells userspace the worst case signal stack size. */ 211 static unsigned long __ro_after_init max_frame_size; 212 static unsigned int __ro_after_init fpu_default_state_size; 213 214 static int __init init_sigframe_size(void) 215 { 216 fpu_default_state_size = fpu__get_fpstate_size(); 217 218 max_frame_size = MAX_FRAME_SIGINFO_UCTXT_SIZE + MAX_FRAME_PADDING; 219 220 max_frame_size += fpu_default_state_size + MAX_XSAVE_PADDING; 221 222 /* Userspace expects an aligned size. */ 223 max_frame_size = round_up(max_frame_size, FRAME_ALIGNMENT); 224 225 pr_info("max sigframe size: %lu\n", max_frame_size); 226 return 0; 227 } 228 early_initcall(init_sigframe_size); 229 230 unsigned long get_sigframe_size(void) 231 { 232 return max_frame_size; 233 } 234 235 static int 236 setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs) 237 { 238 /* Perform fixup for the pre-signal frame. */ 239 rseq_signal_deliver(ksig, regs); 240 241 /* Set up the stack frame */ 242 if (is_ia32_frame(ksig)) { 243 if (ksig->ka.sa.sa_flags & SA_SIGINFO) 244 return ia32_setup_rt_frame(ksig, regs); 245 else 246 return ia32_setup_frame(ksig, regs); 247 } else if (is_x32_frame(ksig)) { 248 return x32_setup_rt_frame(ksig, regs); 249 } else { 250 return x64_setup_rt_frame(ksig, regs); 251 } 252 } 253 254 static void 255 handle_signal(struct ksignal *ksig, struct pt_regs *regs) 256 { 257 bool stepping, failed; 258 struct fpu *fpu = ¤t->thread.fpu; 259 260 if (v8086_mode(regs)) 261 save_v86_state((struct kernel_vm86_regs *) regs, VM86_SIGNAL); 262 263 /* Are we from a system call? */ 264 if (syscall_get_nr(current, regs) != -1) { 265 /* If so, check system call restarting.. */ 266 switch (syscall_get_error(current, regs)) { 267 case -ERESTART_RESTARTBLOCK: 268 case -ERESTARTNOHAND: 269 regs->ax = -EINTR; 270 break; 271 272 case -ERESTARTSYS: 273 if (!(ksig->ka.sa.sa_flags & SA_RESTART)) { 274 regs->ax = -EINTR; 275 break; 276 } 277 fallthrough; 278 case -ERESTARTNOINTR: 279 regs->ax = regs->orig_ax; 280 regs->ip -= 2; 281 break; 282 } 283 } 284 285 /* 286 * If TF is set due to a debugger (TIF_FORCED_TF), clear TF now 287 * so that register information in the sigcontext is correct and 288 * then notify the tracer before entering the signal handler. 289 */ 290 stepping = test_thread_flag(TIF_SINGLESTEP); 291 if (stepping) 292 user_disable_single_step(current); 293 294 failed = (setup_rt_frame(ksig, regs) < 0); 295 if (!failed) { 296 /* 297 * Clear the direction flag as per the ABI for function entry. 298 * 299 * Clear RF when entering the signal handler, because 300 * it might disable possible debug exception from the 301 * signal handler. 302 * 303 * Clear TF for the case when it wasn't set by debugger to 304 * avoid the recursive send_sigtrap() in SIGTRAP handler. 305 */ 306 regs->flags &= ~(X86_EFLAGS_DF|X86_EFLAGS_RF|X86_EFLAGS_TF); 307 /* 308 * Ensure the signal handler starts with the new fpu state. 309 */ 310 fpu__clear_user_states(fpu); 311 } 312 signal_setup_done(failed, ksig, stepping); 313 } 314 315 static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs) 316 { 317 #ifdef CONFIG_IA32_EMULATION 318 if (current->restart_block.arch_data & TS_COMPAT) 319 return __NR_ia32_restart_syscall; 320 #endif 321 #ifdef CONFIG_X86_X32_ABI 322 return __NR_restart_syscall | (regs->orig_ax & __X32_SYSCALL_BIT); 323 #else 324 return __NR_restart_syscall; 325 #endif 326 } 327 328 /* 329 * Note that 'init' is a special process: it doesn't get signals it doesn't 330 * want to handle. Thus you cannot kill init even with a SIGKILL even by 331 * mistake. 332 */ 333 void arch_do_signal_or_restart(struct pt_regs *regs) 334 { 335 struct ksignal ksig; 336 337 if (get_signal(&ksig)) { 338 /* Whee! Actually deliver the signal. */ 339 handle_signal(&ksig, regs); 340 return; 341 } 342 343 /* Did we come from a system call? */ 344 if (syscall_get_nr(current, regs) != -1) { 345 /* Restart the system call - no handlers present */ 346 switch (syscall_get_error(current, regs)) { 347 case -ERESTARTNOHAND: 348 case -ERESTARTSYS: 349 case -ERESTARTNOINTR: 350 regs->ax = regs->orig_ax; 351 regs->ip -= 2; 352 break; 353 354 case -ERESTART_RESTARTBLOCK: 355 regs->ax = get_nr_restart_syscall(regs); 356 regs->ip -= 2; 357 break; 358 } 359 } 360 361 /* 362 * If there's no signal to deliver, we just put the saved sigmask 363 * back. 364 */ 365 restore_saved_sigmask(); 366 } 367 368 void signal_fault(struct pt_regs *regs, void __user *frame, char *where) 369 { 370 struct task_struct *me = current; 371 372 if (show_unhandled_signals && printk_ratelimit()) { 373 printk("%s" 374 "%s[%d] bad frame in %s frame:%p ip:%lx sp:%lx orax:%lx", 375 task_pid_nr(current) > 1 ? KERN_INFO : KERN_EMERG, 376 me->comm, me->pid, where, frame, 377 regs->ip, regs->sp, regs->orig_ax); 378 print_vma_addr(KERN_CONT " in ", regs->ip); 379 pr_cont("\n"); 380 } 381 382 force_sig(SIGSEGV); 383 } 384 385 #ifdef CONFIG_DYNAMIC_SIGFRAME 386 #ifdef CONFIG_STRICT_SIGALTSTACK_SIZE 387 static bool strict_sigaltstack_size __ro_after_init = true; 388 #else 389 static bool strict_sigaltstack_size __ro_after_init = false; 390 #endif 391 392 static int __init strict_sas_size(char *arg) 393 { 394 return kstrtobool(arg, &strict_sigaltstack_size) == 0; 395 } 396 __setup("strict_sas_size", strict_sas_size); 397 398 /* 399 * MINSIGSTKSZ is 2048 and can't be changed despite the fact that AVX512 400 * exceeds that size already. As such programs might never use the 401 * sigaltstack they just continued to work. While always checking against 402 * the real size would be correct, this might be considered a regression. 403 * 404 * Therefore avoid the sanity check, unless enforced by kernel 405 * configuration or command line option. 406 * 407 * When dynamic FPU features are supported, the check is also enforced when 408 * the task has permissions to use dynamic features. Tasks which have no 409 * permission are checked against the size of the non-dynamic feature set 410 * if strict checking is enabled. This avoids forcing all tasks on the 411 * system to allocate large sigaltstacks even if they are never going 412 * to use a dynamic feature. As this is serialized via sighand::siglock 413 * any permission request for a dynamic feature either happened already 414 * or will see the newly install sigaltstack size in the permission checks. 415 */ 416 bool sigaltstack_size_valid(size_t ss_size) 417 { 418 unsigned long fsize = max_frame_size - fpu_default_state_size; 419 u64 mask; 420 421 lockdep_assert_held(¤t->sighand->siglock); 422 423 if (!fpu_state_size_dynamic() && !strict_sigaltstack_size) 424 return true; 425 426 fsize += current->group_leader->thread.fpu.perm.__user_state_size; 427 if (likely(ss_size > fsize)) 428 return true; 429 430 if (strict_sigaltstack_size) 431 return ss_size > fsize; 432 433 mask = current->group_leader->thread.fpu.perm.__state_perm; 434 if (mask & XFEATURE_MASK_USER_DYNAMIC) 435 return ss_size > fsize; 436 437 return true; 438 } 439 #endif /* CONFIG_DYNAMIC_SIGFRAME */ 440