1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Signal Handling for ARC 4 * 5 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) 6 * 7 * vineetg: Jan 2010 (Restarting of timer related syscalls) 8 * 9 * vineetg: Nov 2009 (Everything needed for TIF_RESTORE_SIGMASK) 10 * -do_signal() supports TIF_RESTORE_SIGMASK 11 * -do_signal() no loner needs oldset, required by OLD sys_sigsuspend 12 * -sys_rt_sigsuspend() now comes from generic code, so discard arch implemen 13 * -sys_sigsuspend() no longer needs to fudge ptregs, hence that arg removed 14 * -sys_sigsuspend() no longer loops for do_signal(), sets TIF_xxx and leaves 15 * the job to do_signal() 16 * 17 * vineetg: July 2009 18 * -Modified Code to support the uClibc provided userland sigreturn stub 19 * to avoid kernel synthesing it on user stack at runtime, costing TLB 20 * probes and Cache line flushes. 21 * 22 * vineetg: July 2009 23 * -In stash_usr_regs( ) and restore_usr_regs( ), save/restore of user regs 24 * in done in block copy rather than one word at a time. 25 * This saves around 2K of code and improves LMBench lat_sig <catch> 26 * 27 * rajeshwarr: Feb 2009 28 * - Support for Realtime Signals 29 * 30 * vineetg: Aug 11th 2008: Bug #94183 31 * -ViXS were still seeing crashes when using insmod to load drivers. 32 * It turned out that the code to change Execute permssions for TLB entries 33 * of user was not guarded for interrupts (mod_tlb_permission) 34 * This was causing TLB entries to be overwritten on unrelated indexes 35 * 36 * Vineetg: July 15th 2008: Bug #94183 37 * -Exception happens in Delay slot of a JMP, and before user space resumes, 38 * Signal is delivered (Ctrl + C) = >SIGINT. 39 * setup_frame( ) sets up PC,SP,BLINK to enable user space signal handler 40 * to run, but doesn't clear the Delay slot bit from status32. As a result, 41 * on resuming user mode, signal handler branches off to BTA of orig JMP 42 * -FIX: clear the DE bit from status32 in setup_frame( ) 43 * 44 * Rahul Trivedi, Kanika Nema: Codito Technologies 2004 45 */ 46 47 #include <linux/signal.h> 48 #include <linux/ptrace.h> 49 #include <linux/personality.h> 50 #include <linux/uaccess.h> 51 #include <linux/syscalls.h> 52 #include <linux/tracehook.h> 53 #include <linux/sched/task_stack.h> 54 55 #include <asm/ucontext.h> 56 57 struct rt_sigframe { 58 struct siginfo info; 59 struct ucontext uc; 60 #define MAGIC_SIGALTSTK 0x07302004 61 unsigned int sigret_magic; 62 }; 63 64 static int 65 stash_usr_regs(struct rt_sigframe __user *sf, struct pt_regs *regs, 66 sigset_t *set) 67 { 68 int err; 69 struct user_regs_struct uregs; 70 71 uregs.scratch.bta = regs->bta; 72 uregs.scratch.lp_start = regs->lp_start; 73 uregs.scratch.lp_end = regs->lp_end; 74 uregs.scratch.lp_count = regs->lp_count; 75 uregs.scratch.status32 = regs->status32; 76 uregs.scratch.ret = regs->ret; 77 uregs.scratch.blink = regs->blink; 78 uregs.scratch.fp = regs->fp; 79 uregs.scratch.gp = regs->r26; 80 uregs.scratch.r12 = regs->r12; 81 uregs.scratch.r11 = regs->r11; 82 uregs.scratch.r10 = regs->r10; 83 uregs.scratch.r9 = regs->r9; 84 uregs.scratch.r8 = regs->r8; 85 uregs.scratch.r7 = regs->r7; 86 uregs.scratch.r6 = regs->r6; 87 uregs.scratch.r5 = regs->r5; 88 uregs.scratch.r4 = regs->r4; 89 uregs.scratch.r3 = regs->r3; 90 uregs.scratch.r2 = regs->r2; 91 uregs.scratch.r1 = regs->r1; 92 uregs.scratch.r0 = regs->r0; 93 uregs.scratch.sp = regs->sp; 94 95 err = __copy_to_user(&(sf->uc.uc_mcontext.regs.scratch), &uregs.scratch, 96 sizeof(sf->uc.uc_mcontext.regs.scratch)); 97 err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(sigset_t)); 98 99 return err; 100 } 101 102 static int restore_usr_regs(struct pt_regs *regs, struct rt_sigframe __user *sf) 103 { 104 sigset_t set; 105 int err; 106 struct user_regs_struct uregs; 107 108 err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set)); 109 err |= __copy_from_user(&uregs.scratch, 110 &(sf->uc.uc_mcontext.regs.scratch), 111 sizeof(sf->uc.uc_mcontext.regs.scratch)); 112 if (err) 113 return err; 114 115 set_current_blocked(&set); 116 regs->bta = uregs.scratch.bta; 117 regs->lp_start = uregs.scratch.lp_start; 118 regs->lp_end = uregs.scratch.lp_end; 119 regs->lp_count = uregs.scratch.lp_count; 120 regs->status32 = uregs.scratch.status32; 121 regs->ret = uregs.scratch.ret; 122 regs->blink = uregs.scratch.blink; 123 regs->fp = uregs.scratch.fp; 124 regs->r26 = uregs.scratch.gp; 125 regs->r12 = uregs.scratch.r12; 126 regs->r11 = uregs.scratch.r11; 127 regs->r10 = uregs.scratch.r10; 128 regs->r9 = uregs.scratch.r9; 129 regs->r8 = uregs.scratch.r8; 130 regs->r7 = uregs.scratch.r7; 131 regs->r6 = uregs.scratch.r6; 132 regs->r5 = uregs.scratch.r5; 133 regs->r4 = uregs.scratch.r4; 134 regs->r3 = uregs.scratch.r3; 135 regs->r2 = uregs.scratch.r2; 136 regs->r1 = uregs.scratch.r1; 137 regs->r0 = uregs.scratch.r0; 138 regs->sp = uregs.scratch.sp; 139 140 return 0; 141 } 142 143 static inline int is_do_ss_needed(unsigned int magic) 144 { 145 if (MAGIC_SIGALTSTK == magic) 146 return 1; 147 else 148 return 0; 149 } 150 151 SYSCALL_DEFINE0(rt_sigreturn) 152 { 153 struct rt_sigframe __user *sf; 154 unsigned int magic; 155 struct pt_regs *regs = current_pt_regs(); 156 157 /* Always make any pending restarted system calls return -EINTR */ 158 current->restart_block.fn = do_no_restart_syscall; 159 160 /* Since we stacked the signal on a word boundary, 161 * then 'sp' should be word aligned here. If it's 162 * not, then the user is trying to mess with us. 163 */ 164 if (regs->sp & 3) 165 goto badframe; 166 167 sf = (struct rt_sigframe __force __user *)(regs->sp); 168 169 if (!access_ok(sf, sizeof(*sf))) 170 goto badframe; 171 172 if (__get_user(magic, &sf->sigret_magic)) 173 goto badframe; 174 175 if (unlikely(is_do_ss_needed(magic))) 176 if (restore_altstack(&sf->uc.uc_stack)) 177 goto badframe; 178 179 if (restore_usr_regs(regs, sf)) 180 goto badframe; 181 182 /* Don't restart from sigreturn */ 183 syscall_wont_restart(regs); 184 185 /* 186 * Ensure that sigreturn always returns to user mode (in case the 187 * regs saved on user stack got fudged between save and sigreturn) 188 * Otherwise it is easy to panic the kernel with a custom 189 * signal handler and/or restorer which clobberes the status32/ret 190 * to return to a bogus location in kernel mode. 191 */ 192 regs->status32 |= STATUS_U_MASK; 193 194 return regs->r0; 195 196 badframe: 197 force_sig(SIGSEGV); 198 return 0; 199 } 200 201 /* 202 * Determine which stack to use.. 203 */ 204 static inline void __user *get_sigframe(struct ksignal *ksig, 205 struct pt_regs *regs, 206 unsigned long framesize) 207 { 208 unsigned long sp = sigsp(regs->sp, ksig); 209 void __user *frame; 210 211 /* No matter what happens, 'sp' must be word 212 * aligned otherwise nasty things could happen 213 */ 214 215 /* ATPCS B01 mandates 8-byte alignment */ 216 frame = (void __user *)((sp - framesize) & ~7); 217 218 /* Check that we can actually write to the signal frame */ 219 if (!access_ok(frame, framesize)) 220 frame = NULL; 221 222 return frame; 223 } 224 225 static int 226 setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs) 227 { 228 struct rt_sigframe __user *sf; 229 unsigned int magic = 0; 230 int err = 0; 231 232 sf = get_sigframe(ksig, regs, sizeof(struct rt_sigframe)); 233 if (!sf) 234 return 1; 235 236 /* 237 * w/o SA_SIGINFO, struct ucontext is partially populated (only 238 * uc_mcontext/uc_sigmask) for kernel's normal user state preservation 239 * during signal handler execution. This works for SA_SIGINFO as well 240 * although the semantics are now overloaded (the same reg state can be 241 * inspected by userland: but are they allowed to fiddle with it ? 242 */ 243 err |= stash_usr_regs(sf, regs, set); 244 245 /* 246 * SA_SIGINFO requires 3 args to signal handler: 247 * #1: sig-no (common to any handler) 248 * #2: struct siginfo 249 * #3: struct ucontext (completely populated) 250 */ 251 if (unlikely(ksig->ka.sa.sa_flags & SA_SIGINFO)) { 252 err |= copy_siginfo_to_user(&sf->info, &ksig->info); 253 err |= __put_user(0, &sf->uc.uc_flags); 254 err |= __put_user(NULL, &sf->uc.uc_link); 255 err |= __save_altstack(&sf->uc.uc_stack, regs->sp); 256 257 /* setup args 2 and 3 for user mode handler */ 258 regs->r1 = (unsigned long)&sf->info; 259 regs->r2 = (unsigned long)&sf->uc; 260 261 /* 262 * small optim to avoid unconditonally calling do_sigaltstack 263 * in sigreturn path, now that we only have rt_sigreturn 264 */ 265 magic = MAGIC_SIGALTSTK; 266 } 267 268 err |= __put_user(magic, &sf->sigret_magic); 269 if (err) 270 return err; 271 272 /* #1 arg to the user Signal handler */ 273 regs->r0 = ksig->sig; 274 275 /* setup PC of user space signal handler */ 276 regs->ret = (unsigned long)ksig->ka.sa.sa_handler; 277 278 /* 279 * handler returns using sigreturn stub provided already by userpsace 280 * If not, nuke the process right away 281 */ 282 if(!(ksig->ka.sa.sa_flags & SA_RESTORER)) 283 return 1; 284 285 regs->blink = (unsigned long)ksig->ka.sa.sa_restorer; 286 287 /* User Stack for signal handler will be above the frame just carved */ 288 regs->sp = (unsigned long)sf; 289 290 /* 291 * Bug 94183, Clear the DE bit, so that when signal handler 292 * starts to run, it doesn't use BTA 293 */ 294 regs->status32 &= ~STATUS_DE_MASK; 295 regs->status32 |= STATUS_L_MASK; 296 297 return err; 298 } 299 300 static void arc_restart_syscall(struct k_sigaction *ka, struct pt_regs *regs) 301 { 302 switch (regs->r0) { 303 case -ERESTART_RESTARTBLOCK: 304 case -ERESTARTNOHAND: 305 /* 306 * ERESTARTNOHAND means that the syscall should 307 * only be restarted if there was no handler for 308 * the signal, and since we only get here if there 309 * is a handler, we don't restart 310 */ 311 regs->r0 = -EINTR; /* ERESTART_xxx is internal */ 312 break; 313 314 case -ERESTARTSYS: 315 /* 316 * ERESTARTSYS means to restart the syscall if 317 * there is no handler or the handler was 318 * registered with SA_RESTART 319 */ 320 if (!(ka->sa.sa_flags & SA_RESTART)) { 321 regs->r0 = -EINTR; 322 break; 323 } 324 fallthrough; 325 326 case -ERESTARTNOINTR: 327 /* 328 * ERESTARTNOINTR means that the syscall should 329 * be called again after the signal handler returns. 330 * Setup reg state just as it was before doing the trap 331 * r0 has been clobbered with sys call ret code thus it 332 * needs to be reloaded with orig first arg to syscall 333 * in orig_r0. Rest of relevant reg-file: 334 * r8 (syscall num) and (r1 - r7) will be reset to 335 * their orig user space value when we ret from kernel 336 */ 337 regs->r0 = regs->orig_r0; 338 regs->ret -= is_isa_arcv2() ? 2 : 4; 339 break; 340 } 341 } 342 343 /* 344 * OK, we're invoking a handler 345 */ 346 static void 347 handle_signal(struct ksignal *ksig, struct pt_regs *regs) 348 { 349 sigset_t *oldset = sigmask_to_save(); 350 int failed; 351 352 /* Set up the stack frame */ 353 failed = setup_rt_frame(ksig, oldset, regs); 354 355 signal_setup_done(failed, ksig, 0); 356 } 357 358 void do_signal(struct pt_regs *regs) 359 { 360 struct ksignal ksig; 361 int restart_scall; 362 363 restart_scall = in_syscall(regs) && syscall_restartable(regs); 364 365 if (test_thread_flag(TIF_SIGPENDING) && get_signal(&ksig)) { 366 if (restart_scall) { 367 arc_restart_syscall(&ksig.ka, regs); 368 syscall_wont_restart(regs); /* No more restarts */ 369 } 370 handle_signal(&ksig, regs); 371 return; 372 } 373 374 if (restart_scall) { 375 /* No handler for syscall: restart it */ 376 if (regs->r0 == -ERESTARTNOHAND || 377 regs->r0 == -ERESTARTSYS || regs->r0 == -ERESTARTNOINTR) { 378 regs->r0 = regs->orig_r0; 379 regs->ret -= is_isa_arcv2() ? 2 : 4; 380 } else if (regs->r0 == -ERESTART_RESTARTBLOCK) { 381 regs->r8 = __NR_restart_syscall; 382 regs->ret -= is_isa_arcv2() ? 2 : 4; 383 } 384 syscall_wont_restart(regs); /* No more restarts */ 385 } 386 387 /* If there's no signal to deliver, restore the saved sigmask back */ 388 restore_saved_sigmask(); 389 } 390 391 void do_notify_resume(struct pt_regs *regs) 392 { 393 /* 394 * ASM glue gaurantees that this is only called when returning to 395 * user mode 396 */ 397 if (test_thread_flag(TIF_NOTIFY_RESUME)) 398 tracehook_notify_resume(regs); 399 } 400