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