arch/arc/kernel/signal.c

   1 /*
   2  * Signal Handling for ARC
   3  *
   4  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  *
  10  * vineetg: Jan 2010 (Restarting of timer related syscalls)
  11  *
  12  * vineetg: Nov 2009 (Everything needed for TIF_RESTORE_SIGMASK)
  13  *  -do_signal() supports TIF_RESTORE_SIGMASK
  14  *  -do_signal() no loner needs oldset, required by OLD sys_sigsuspend
  15  *  -sys_rt_sigsuspend() now comes from generic code, so discard arch implemen
  16  *  -sys_sigsuspend() no longer needs to fudge ptregs, hence that arg removed
  17  *  -sys_sigsuspend() no longer loops for do_signal(), sets TIF_xxx and leaves
  18  *   the job to do_signal()
  19  *
  20  * vineetg: July 2009
  21  *  -Modified Code to support the uClibc provided userland sigreturn stub
  22  *   to avoid kernel synthesing it on user stack at runtime, costing TLB
  23  *   probes and Cache line flushes.
  24  *
  25  * vineetg: July 2009
  26  *  -In stash_usr_regs( ) and restore_usr_regs( ), save/restore of user regs
  27  *   in done in block copy rather than one word at a time.
  28  *   This saves around 2K of code and improves LMBench lat_sig <catch>
  29  *
  30  * rajeshwarr: Feb 2009
  31  *  - Support for Realtime Signals
  32  *
  33  * vineetg: Aug 11th 2008: Bug #94183
  34  *  -ViXS were still seeing crashes when using insmod to load drivers.
  35  *   It turned out that the code to change Execute permssions for TLB entries
  36  *   of user was not guarded for interrupts (mod_tlb_permission)
  37  *   This was causing TLB entries to be overwritten on unrelated indexes
  38  *
  39  * Vineetg: July 15th 2008: Bug #94183
  40  *  -Exception happens in Delay slot of a JMP, and before user space resumes,
  41  *   Signal is delivered (Ctrl + C) = >SIGINT.
  42  *   setup_frame( ) sets up PC,SP,BLINK to enable user space signal handler
  43  *   to run, but doesn't clear the Delay slot bit from status32. As a result,
  44  *   on resuming user mode, signal handler branches off to BTA of orig JMP
  45  *  -FIX: clear the DE bit from status32 in setup_frame( )
  46  *
  47  * Rahul Trivedi, Kanika Nema: Codito Technologies 2004
  48  */
  49
  50 #include <linux/signal.h>
  51 #include <linux/ptrace.h>
  52 #include <linux/personality.h>
  53 #include <linux/uaccess.h>
  54 #include <linux/syscalls.h>
  55 #include <linux/tracehook.h>
  56 #include <linux/sched/task_stack.h>
  57
  58 #include <asm/ucontext.h>
  59
  60 struct rt_sigframe {
  61         struct siginfo info;
  62         struct ucontext uc;
  63 #define MAGIC_SIGALTSTK         0x07302004
  64         unsigned int sigret_magic;
  65 };
  66
  67 static int
  68 stash_usr_regs(struct rt_sigframe __user *sf, struct pt_regs *regs,
  69                sigset_t *set)
  70 {
  71         int err;
  72         struct user_regs_struct uregs;
  73
  74         uregs.scratch.bta       = regs->bta;
  75         uregs.scratch.lp_start  = regs->lp_start;
  76         uregs.scratch.lp_end    = regs->lp_end;
  77         uregs.scratch.lp_count  = regs->lp_count;
  78         uregs.scratch.status32  = regs->status32;
  79         uregs.scratch.ret       = regs->ret;
  80         uregs.scratch.blink     = regs->blink;
  81         uregs.scratch.fp        = regs->fp;
  82         uregs.scratch.gp        = regs->r26;
  83         uregs.scratch.r12       = regs->r12;
  84         uregs.scratch.r11       = regs->r11;
  85         uregs.scratch.r10       = regs->r10;
  86         uregs.scratch.r9        = regs->r9;
  87         uregs.scratch.r8        = regs->r8;
  88         uregs.scratch.r7        = regs->r7;
  89         uregs.scratch.r6        = regs->r6;
  90         uregs.scratch.r5        = regs->r5;
  91         uregs.scratch.r4        = regs->r4;
  92         uregs.scratch.r3        = regs->r3;
  93         uregs.scratch.r2        = regs->r2;
  94         uregs.scratch.r1        = regs->r1;
  95         uregs.scratch.r0        = regs->r0;
  96         uregs.scratch.sp        = regs->sp;
  97
  98         err = __copy_to_user(&(sf->uc.uc_mcontext.regs.scratch), &uregs.scratch,
  99                              sizeof(sf->uc.uc_mcontext.regs.scratch));
 100         err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(sigset_t));
 101
 102         return err;
 103 }
 104
 105 static int restore_usr_regs(struct pt_regs *regs, struct rt_sigframe __user *sf)
 106 {
 107         sigset_t set;
 108         int err;
 109         struct user_regs_struct uregs;
 110
 111         err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
 112         err |= __copy_from_user(&uregs.scratch,
 113                                 &(sf->uc.uc_mcontext.regs.scratch),
 114                                 sizeof(sf->uc.uc_mcontext.regs.scratch));
 115         if (err)
 116                 return err;
 117
 118         set_current_blocked(&set);
 119         regs->bta       = uregs.scratch.bta;
 120         regs->lp_start  = uregs.scratch.lp_start;
 121         regs->lp_end    = uregs.scratch.lp_end;
 122         regs->lp_count  = uregs.scratch.lp_count;
 123         regs->status32  = uregs.scratch.status32;
 124         regs->ret       = uregs.scratch.ret;
 125         regs->blink     = uregs.scratch.blink;
 126         regs->fp        = uregs.scratch.fp;
 127         regs->r26       = uregs.scratch.gp;
 128         regs->r12       = uregs.scratch.r12;
 129         regs->r11       = uregs.scratch.r11;
 130         regs->r10       = uregs.scratch.r10;
 131         regs->r9        = uregs.scratch.r9;
 132         regs->r8        = uregs.scratch.r8;
 133         regs->r7        = uregs.scratch.r7;
 134         regs->r6        = uregs.scratch.r6;
 135         regs->r5        = uregs.scratch.r5;
 136         regs->r4        = uregs.scratch.r4;
 137         regs->r3        = uregs.scratch.r3;
 138         regs->r2        = uregs.scratch.r2;
 139         regs->r1        = uregs.scratch.r1;
 140         regs->r0        = uregs.scratch.r0;
 141         regs->sp        = uregs.scratch.sp;
 142
 143         return 0;
 144 }
 145
 146 static inline int is_do_ss_needed(unsigned int magic)
 147 {
 148         if (MAGIC_SIGALTSTK == magic)
 149                 return 1;
 150         else
 151                 return 0;
 152 }
 153
 154 SYSCALL_DEFINE0(rt_sigreturn)
 155 {
 156         struct rt_sigframe __user *sf;
 157         unsigned int magic;
 158         struct pt_regs *regs = current_pt_regs();
 159
 160         /* Always make any pending restarted system calls return -EINTR */
 161         current->restart_block.fn = do_no_restart_syscall;
 162
 163         /* Since we stacked the signal on a word boundary,
 164          * then 'sp' should be word aligned here.  If it's
 165          * not, then the user is trying to mess with us.
 166          */
 167         if (regs->sp & 3)
 168                 goto badframe;
 169
 170         sf = (struct rt_sigframe __force __user *)(regs->sp);
 171
 172         if (!access_ok(sf, sizeof(*sf)))
 173                 goto badframe;
 174
 175         if (__get_user(magic, &sf->sigret_magic))
 176                 goto badframe;
 177
 178         if (unlikely(is_do_ss_needed(magic)))
 179                 if (restore_altstack(&sf->uc.uc_stack))
 180                         goto badframe;
 181
 182         if (restore_usr_regs(regs, sf))
 183                 goto badframe;
 184
 185         /* Don't restart from sigreturn */
 186         syscall_wont_restart(regs);
 187
 188         /*
 189          * Ensure that sigreturn always returns to user mode (in case the
 190          * regs saved on user stack got fudged between save and sigreturn)
 191          * Otherwise it is easy to panic the kernel with a custom
 192          * signal handler and/or restorer which clobberes the status32/ret
 193          * to return to a bogus location in kernel mode.
 194          */
 195         regs->status32 |= STATUS_U_MASK;
 196
 197         return regs->r0;
 198
 199 badframe:
 200         force_sig(SIGSEGV, current);
 201         return 0;
 202 }
 203
 204 /*
 205  * Determine which stack to use..
 206  */
 207 static inline void __user *get_sigframe(struct ksignal *ksig,
 208                                         struct pt_regs *regs,
 209                                         unsigned long framesize)
 210 {
 211         unsigned long sp = sigsp(regs->sp, ksig);
 212         void __user *frame;
 213
 214         /* No matter what happens, 'sp' must be word
 215          * aligned otherwise nasty things could happen
 216          */
 217
 218         /* ATPCS B01 mandates 8-byte alignment */
 219         frame = (void __user *)((sp - framesize) & ~7);
 220
 221         /* Check that we can actually write to the signal frame */
 222         if (!access_ok(frame, framesize))
 223                 frame = NULL;
 224
 225         return frame;
 226 }
 227
 228 static int
 229 setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
 230 {
 231         struct rt_sigframe __user *sf;
 232         unsigned int magic = 0;
 233         int err = 0;
 234
 235         sf = get_sigframe(ksig, regs, sizeof(struct rt_sigframe));
 236         if (!sf)
 237                 return 1;
 238
 239         /*
 240          * w/o SA_SIGINFO, struct ucontext is partially populated (only
 241          * uc_mcontext/uc_sigmask) for kernel's normal user state preservation
 242          * during signal handler execution. This works for SA_SIGINFO as well
 243          * although the semantics are now overloaded (the same reg state can be
 244          * inspected by userland: but are they allowed to fiddle with it ?
 245          */
 246         err |= stash_usr_regs(sf, regs, set);
 247
 248         /*
 249          * SA_SIGINFO requires 3 args to signal handler:
 250          *  #1: sig-no (common to any handler)
 251          *  #2: struct siginfo
 252          *  #3: struct ucontext (completely populated)
 253          */
 254         if (unlikely(ksig->ka.sa.sa_flags & SA_SIGINFO)) {
 255                 err |= copy_siginfo_to_user(&sf->info, &ksig->info);
 256                 err |= __put_user(0, &sf->uc.uc_flags);
 257                 err |= __put_user(NULL, &sf->uc.uc_link);
 258                 err |= __save_altstack(&sf->uc.uc_stack, regs->sp);
 259
 260                 /* setup args 2 and 3 for user mode handler */
 261                 regs->r1 = (unsigned long)&sf->info;
 262                 regs->r2 = (unsigned long)&sf->uc;
 263
 264                 /*
 265                  * small optim to avoid unconditonally calling do_sigaltstack
 266                  * in sigreturn path, now that we only have rt_sigreturn
 267                  */
 268                 magic = MAGIC_SIGALTSTK;
 269         }
 270
 271         err |= __put_user(magic, &sf->sigret_magic);
 272         if (err)
 273                 return err;
 274
 275         /* #1 arg to the user Signal handler */
 276         regs->r0 = ksig->sig;
 277
 278         /* setup PC of user space signal handler */
 279         regs->ret = (unsigned long)ksig->ka.sa.sa_handler;
 280
 281         /*
 282          * handler returns using sigreturn stub provided already by userpsace
 283          * If not, nuke the process right away
 284          */
 285         if(!(ksig->ka.sa.sa_flags & SA_RESTORER))
 286                 return 1;
 287
 288         regs->blink = (unsigned long)ksig->ka.sa.sa_restorer;
 289
 290         /* User Stack for signal handler will be above the frame just carved */
 291         regs->sp = (unsigned long)sf;
 292
 293         /*
 294          * Bug 94183, Clear the DE bit, so that when signal handler
 295          * starts to run, it doesn't use BTA
 296          */
 297         regs->status32 &= ~STATUS_DE_MASK;
 298         regs->status32 |= STATUS_L_MASK;
 299
 300         return err;
 301 }
 302
 303 static void arc_restart_syscall(struct k_sigaction *ka, struct pt_regs *regs)
 304 {
 305         switch (regs->r0) {
 306         case -ERESTART_RESTARTBLOCK:
 307         case -ERESTARTNOHAND:
 308                 /*
 309                  * ERESTARTNOHAND means that the syscall should
 310                  * only be restarted if there was no handler for
 311                  * the signal, and since we only get here if there
 312                  * is a handler, we don't restart
 313                  */
 314                 regs->r0 = -EINTR;   /* ERESTART_xxx is internal */
 315                 break;
 316
 317         case -ERESTARTSYS:
 318                 /*
 319                  * ERESTARTSYS means to restart the syscall if
 320                  * there is no handler or the handler was
 321                  * registered with SA_RESTART
 322                  */
 323                 if (!(ka->sa.sa_flags & SA_RESTART)) {
 324                         regs->r0 = -EINTR;
 325                         break;
 326                 }
 327                 /* fallthrough */
 328
 329         case -ERESTARTNOINTR:
 330                 /*
 331                  * ERESTARTNOINTR means that the syscall should
 332                  * be called again after the signal handler returns.
 333                  * Setup reg state just as it was before doing the trap
 334                  * r0 has been clobbered with sys call ret code thus it
 335                  * needs to be reloaded with orig first arg to syscall
 336                  * in orig_r0. Rest of relevant reg-file:
 337                  * r8 (syscall num) and (r1 - r7) will be reset to
 338                  * their orig user space value when we ret from kernel
 339                  */
 340                 regs->r0 = regs->orig_r0;
 341                 regs->ret -= is_isa_arcv2() ? 2 : 4;
 342                 break;
 343         }
 344 }
 345
 346 /*
 347  * OK, we're invoking a handler
 348  */
 349 static void
 350 handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 351 {
 352         sigset_t *oldset = sigmask_to_save();
 353         int failed;
 354
 355         /* Set up the stack frame */
 356         failed = setup_rt_frame(ksig, oldset, regs);
 357
 358         signal_setup_done(failed, ksig, 0);
 359 }
 360
 361 void do_signal(struct pt_regs *regs)
 362 {
 363         struct ksignal ksig;
 364         int restart_scall;
 365
 366         restart_scall = in_syscall(regs) && syscall_restartable(regs);
 367
 368         if (get_signal(&ksig)) {
 369                 if (restart_scall) {
 370                         arc_restart_syscall(&ksig.ka, regs);
 371                         syscall_wont_restart(regs);     /* No more restarts */
 372                 }
 373                 handle_signal(&ksig, regs);
 374                 return;
 375         }
 376
 377         if (restart_scall) {
 378                 /* No handler for syscall: restart it */
 379                 if (regs->r0 == -ERESTARTNOHAND ||
 380                     regs->r0 == -ERESTARTSYS || regs->r0 == -ERESTARTNOINTR) {
 381                         regs->r0 = regs->orig_r0;
 382                         regs->ret -= is_isa_arcv2() ? 2 : 4;
 383                 } else if (regs->r0 == -ERESTART_RESTARTBLOCK) {
 384                         regs->r8 = __NR_restart_syscall;
 385                         regs->ret -= is_isa_arcv2() ? 2 : 4;
 386                 }
 387                 syscall_wont_restart(regs);     /* No more restarts */
 388         }
 389
 390         /* If there's no signal to deliver, restore the saved sigmask back */
 391         restore_saved_sigmask();
 392 }
 393
 394 void do_notify_resume(struct pt_regs *regs)
 395 {
 396         /*
 397          * ASM glue gaurantees that this is only called when returning to
 398          * user mode
 399          */
 400         if (test_and_clear_thread_flag(TIF_NOTIFY_RESUME))
 401                 tracehook_notify_resume(regs);
 402 }