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