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 u32 pkru = read_pkru(); 87 88 /* redzone */ 89 if (!ia32_frame) 90 sp -= 128; 91 92 /* This is the X/Open sanctioned signal stack switching. */ 93 if (ka->sa.sa_flags & SA_ONSTACK) { 94 /* 95 * This checks nested_altstack via sas_ss_flags(). Sensible 96 * programs use SS_AUTODISARM, which disables that check, and 97 * programs that don't use SS_AUTODISARM get compatible. 98 */ 99 if (sas_ss_flags(sp) == 0) { 100 sp = current->sas_ss_sp + current->sas_ss_size; 101 entering_altstack = true; 102 } 103 } else if (ia32_frame && 104 !nested_altstack && 105 regs->ss != __USER_DS && 106 !(ka->sa.sa_flags & SA_RESTORER) && 107 ka->sa.sa_restorer) { 108 /* This is the legacy signal stack switching. */ 109 sp = (unsigned long) ka->sa.sa_restorer; 110 entering_altstack = true; 111 } 112 113 sp = fpu__alloc_mathframe(sp, ia32_frame, &buf_fx, &math_size); 114 *fpstate = (void __user *)sp; 115 116 sp -= frame_size; 117 118 if (ia32_frame) 119 /* 120 * Align the stack pointer according to the i386 ABI, 121 * i.e. so that on function entry ((sp + 4) & 15) == 0. 122 */ 123 sp = ((sp + 4) & -FRAME_ALIGNMENT) - 4; 124 else 125 sp = round_down(sp, FRAME_ALIGNMENT) - 8; 126 127 /* 128 * If we are on the alternate signal stack and would overflow it, don't. 129 * Return an always-bogus address instead so we will die with SIGSEGV. 130 */ 131 if (unlikely((nested_altstack || entering_altstack) && 132 !__on_sig_stack(sp))) { 133 134 if (show_unhandled_signals && printk_ratelimit()) 135 pr_info("%s[%d] overflowed sigaltstack\n", 136 current->comm, task_pid_nr(current)); 137 138 return (void __user *)-1L; 139 } 140 141 /* save i387 and extended state */ 142 if (!copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size, pkru)) 143 return (void __user *)-1L; 144 145 return (void __user *)sp; 146 } 147 148 /* 149 * There are four different struct types for signal frame: sigframe_ia32, 150 * rt_sigframe_ia32, rt_sigframe_x32, and rt_sigframe. Use the worst case 151 * -- the largest size. It means the size for 64-bit apps is a bit more 152 * than needed, but this keeps the code simple. 153 */ 154 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) 155 # define MAX_FRAME_SIGINFO_UCTXT_SIZE sizeof(struct sigframe_ia32) 156 #else 157 # define MAX_FRAME_SIGINFO_UCTXT_SIZE sizeof(struct rt_sigframe) 158 #endif 159 160 /* 161 * The FP state frame contains an XSAVE buffer which must be 64-byte aligned. 162 * If a signal frame starts at an unaligned address, extra space is required. 163 * This is the max alignment padding, conservatively. 164 */ 165 #define MAX_XSAVE_PADDING 63UL 166 167 /* 168 * The frame data is composed of the following areas and laid out as: 169 * 170 * ------------------------- 171 * | alignment padding | 172 * ------------------------- 173 * | (f)xsave frame | 174 * ------------------------- 175 * | fsave header | 176 * ------------------------- 177 * | alignment padding | 178 * ------------------------- 179 * | siginfo + ucontext | 180 * ------------------------- 181 */ 182 183 /* max_frame_size tells userspace the worst case signal stack size. */ 184 static unsigned long __ro_after_init max_frame_size; 185 static unsigned int __ro_after_init fpu_default_state_size; 186 187 static int __init init_sigframe_size(void) 188 { 189 fpu_default_state_size = fpu__get_fpstate_size(); 190 191 max_frame_size = MAX_FRAME_SIGINFO_UCTXT_SIZE + MAX_FRAME_PADDING; 192 193 max_frame_size += fpu_default_state_size + MAX_XSAVE_PADDING; 194 195 /* Userspace expects an aligned size. */ 196 max_frame_size = round_up(max_frame_size, FRAME_ALIGNMENT); 197 198 pr_info("max sigframe size: %lu\n", max_frame_size); 199 return 0; 200 } 201 early_initcall(init_sigframe_size); 202 203 unsigned long get_sigframe_size(void) 204 { 205 return max_frame_size; 206 } 207 208 static int 209 setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs) 210 { 211 /* Perform fixup for the pre-signal frame. */ 212 rseq_signal_deliver(ksig, regs); 213 214 /* Set up the stack frame */ 215 if (is_ia32_frame(ksig)) { 216 if (ksig->ka.sa.sa_flags & SA_SIGINFO) 217 return ia32_setup_rt_frame(ksig, regs); 218 else 219 return ia32_setup_frame(ksig, regs); 220 } else if (is_x32_frame(ksig)) { 221 return x32_setup_rt_frame(ksig, regs); 222 } else { 223 return x64_setup_rt_frame(ksig, regs); 224 } 225 } 226 227 static void 228 handle_signal(struct ksignal *ksig, struct pt_regs *regs) 229 { 230 bool stepping, failed; 231 struct fpu *fpu = ¤t->thread.fpu; 232 233 if (v8086_mode(regs)) 234 save_v86_state((struct kernel_vm86_regs *) regs, VM86_SIGNAL); 235 236 /* Are we from a system call? */ 237 if (syscall_get_nr(current, regs) != -1) { 238 /* If so, check system call restarting.. */ 239 switch (syscall_get_error(current, regs)) { 240 case -ERESTART_RESTARTBLOCK: 241 case -ERESTARTNOHAND: 242 regs->ax = -EINTR; 243 break; 244 245 case -ERESTARTSYS: 246 if (!(ksig->ka.sa.sa_flags & SA_RESTART)) { 247 regs->ax = -EINTR; 248 break; 249 } 250 fallthrough; 251 case -ERESTARTNOINTR: 252 regs->ax = regs->orig_ax; 253 regs->ip -= 2; 254 break; 255 } 256 } 257 258 /* 259 * If TF is set due to a debugger (TIF_FORCED_TF), clear TF now 260 * so that register information in the sigcontext is correct and 261 * then notify the tracer before entering the signal handler. 262 */ 263 stepping = test_thread_flag(TIF_SINGLESTEP); 264 if (stepping) 265 user_disable_single_step(current); 266 267 failed = (setup_rt_frame(ksig, regs) < 0); 268 if (!failed) { 269 /* 270 * Clear the direction flag as per the ABI for function entry. 271 * 272 * Clear RF when entering the signal handler, because 273 * it might disable possible debug exception from the 274 * signal handler. 275 * 276 * Clear TF for the case when it wasn't set by debugger to 277 * avoid the recursive send_sigtrap() in SIGTRAP handler. 278 */ 279 regs->flags &= ~(X86_EFLAGS_DF|X86_EFLAGS_RF|X86_EFLAGS_TF); 280 /* 281 * Ensure the signal handler starts with the new fpu state. 282 */ 283 fpu__clear_user_states(fpu); 284 } 285 signal_setup_done(failed, ksig, stepping); 286 } 287 288 static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs) 289 { 290 #ifdef CONFIG_IA32_EMULATION 291 if (current->restart_block.arch_data & TS_COMPAT) 292 return __NR_ia32_restart_syscall; 293 #endif 294 #ifdef CONFIG_X86_X32_ABI 295 return __NR_restart_syscall | (regs->orig_ax & __X32_SYSCALL_BIT); 296 #else 297 return __NR_restart_syscall; 298 #endif 299 } 300 301 /* 302 * Note that 'init' is a special process: it doesn't get signals it doesn't 303 * want to handle. Thus you cannot kill init even with a SIGKILL even by 304 * mistake. 305 */ 306 void arch_do_signal_or_restart(struct pt_regs *regs) 307 { 308 struct ksignal ksig; 309 310 if (get_signal(&ksig)) { 311 /* Whee! Actually deliver the signal. */ 312 handle_signal(&ksig, regs); 313 return; 314 } 315 316 /* Did we come from a system call? */ 317 if (syscall_get_nr(current, regs) != -1) { 318 /* Restart the system call - no handlers present */ 319 switch (syscall_get_error(current, regs)) { 320 case -ERESTARTNOHAND: 321 case -ERESTARTSYS: 322 case -ERESTARTNOINTR: 323 regs->ax = regs->orig_ax; 324 regs->ip -= 2; 325 break; 326 327 case -ERESTART_RESTARTBLOCK: 328 regs->ax = get_nr_restart_syscall(regs); 329 regs->ip -= 2; 330 break; 331 } 332 } 333 334 /* 335 * If there's no signal to deliver, we just put the saved sigmask 336 * back. 337 */ 338 restore_saved_sigmask(); 339 } 340 341 void signal_fault(struct pt_regs *regs, void __user *frame, char *where) 342 { 343 struct task_struct *me = current; 344 345 if (show_unhandled_signals && printk_ratelimit()) { 346 printk("%s" 347 "%s[%d] bad frame in %s frame:%p ip:%lx sp:%lx orax:%lx", 348 task_pid_nr(current) > 1 ? KERN_INFO : KERN_EMERG, 349 me->comm, me->pid, where, frame, 350 regs->ip, regs->sp, regs->orig_ax); 351 print_vma_addr(KERN_CONT " in ", regs->ip); 352 pr_cont("\n"); 353 } 354 355 force_sig(SIGSEGV); 356 } 357 358 #ifdef CONFIG_DYNAMIC_SIGFRAME 359 #ifdef CONFIG_STRICT_SIGALTSTACK_SIZE 360 static bool strict_sigaltstack_size __ro_after_init = true; 361 #else 362 static bool strict_sigaltstack_size __ro_after_init = false; 363 #endif 364 365 static int __init strict_sas_size(char *arg) 366 { 367 return kstrtobool(arg, &strict_sigaltstack_size) == 0; 368 } 369 __setup("strict_sas_size", strict_sas_size); 370 371 /* 372 * MINSIGSTKSZ is 2048 and can't be changed despite the fact that AVX512 373 * exceeds that size already. As such programs might never use the 374 * sigaltstack they just continued to work. While always checking against 375 * the real size would be correct, this might be considered a regression. 376 * 377 * Therefore avoid the sanity check, unless enforced by kernel 378 * configuration or command line option. 379 * 380 * When dynamic FPU features are supported, the check is also enforced when 381 * the task has permissions to use dynamic features. Tasks which have no 382 * permission are checked against the size of the non-dynamic feature set 383 * if strict checking is enabled. This avoids forcing all tasks on the 384 * system to allocate large sigaltstacks even if they are never going 385 * to use a dynamic feature. As this is serialized via sighand::siglock 386 * any permission request for a dynamic feature either happened already 387 * or will see the newly install sigaltstack size in the permission checks. 388 */ 389 bool sigaltstack_size_valid(size_t ss_size) 390 { 391 unsigned long fsize = max_frame_size - fpu_default_state_size; 392 u64 mask; 393 394 lockdep_assert_held(¤t->sighand->siglock); 395 396 if (!fpu_state_size_dynamic() && !strict_sigaltstack_size) 397 return true; 398 399 fsize += current->group_leader->thread.fpu.perm.__user_state_size; 400 if (likely(ss_size > fsize)) 401 return true; 402 403 if (strict_sigaltstack_size) 404 return ss_size > fsize; 405 406 mask = current->group_leader->thread.fpu.perm.__state_perm; 407 if (mask & XFEATURE_MASK_USER_DYNAMIC) 408 return ss_size > fsize; 409 410 return true; 411 } 412 #endif /* CONFIG_DYNAMIC_SIGFRAME */ 413