arch/arc/kernel/signal.c

   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 (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_and_clear_thread_flag(TIF_NOTIFY_RESUME))
 398                 tracehook_notify_resume(regs);
 399 }