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 cauing 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 <asm/ucontext.h>
  57
  58 struct rt_sigframe {
  59         struct siginfo info;
  60         struct ucontext uc;
  61 #define MAGIC_SIGALTSTK         0x07302004
  62         unsigned int sigret_magic;
  63 };
  64
  65 static int
  66 stash_usr_regs(struct rt_sigframe __user *sf, struct pt_regs *regs,
  67                sigset_t *set)
  68 {
  69         int err;
  70         struct user_regs_struct uregs;
  71
  72         uregs.scratch.bta       = regs->bta;
  73         uregs.scratch.lp_start  = regs->lp_start;
  74         uregs.scratch.lp_end    = regs->lp_end;
  75         uregs.scratch.lp_count  = regs->lp_count;
  76         uregs.scratch.status32  = regs->status32;
  77         uregs.scratch.ret       = regs->ret;
  78         uregs.scratch.blink     = regs->blink;
  79         uregs.scratch.fp        = regs->fp;
  80         uregs.scratch.gp        = regs->r26;
  81         uregs.scratch.r12       = regs->r12;
  82         uregs.scratch.r11       = regs->r11;
  83         uregs.scratch.r10       = regs->r10;
  84         uregs.scratch.r9        = regs->r9;
  85         uregs.scratch.r8        = regs->r8;
  86         uregs.scratch.r7        = regs->r7;
  87         uregs.scratch.r6        = regs->r6;
  88         uregs.scratch.r5        = regs->r5;
  89         uregs.scratch.r4        = regs->r4;
  90         uregs.scratch.r3        = regs->r3;
  91         uregs.scratch.r2        = regs->r2;
  92         uregs.scratch.r1        = regs->r1;
  93         uregs.scratch.r0        = regs->r0;
  94         uregs.scratch.sp        = regs->sp;
  95
  96         err = __copy_to_user(&(sf->uc.uc_mcontext.regs.scratch), &uregs.scratch,
  97                              sizeof(sf->uc.uc_mcontext.regs.scratch));
  98         err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(sigset_t));
  99
 100         return err;
 101 }
 102
 103 static int restore_usr_regs(struct pt_regs *regs, struct rt_sigframe __user *sf)
 104 {
 105         sigset_t set;
 106         int err;
 107         struct user_regs_struct uregs;
 108
 109         err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
 110         if (!err)
 111                 set_current_blocked(&set);
 112
 113         err |= __copy_from_user(&uregs.scratch,
 114                                 &(sf->uc.uc_mcontext.regs.scratch),
 115                                 sizeof(sf->uc.uc_mcontext.regs.scratch));
 116
 117         regs->bta       = uregs.scratch.bta;
 118         regs->lp_start  = uregs.scratch.lp_start;
 119         regs->lp_end    = uregs.scratch.lp_end;
 120         regs->lp_count  = uregs.scratch.lp_count;
 121         regs->status32  = uregs.scratch.status32;
 122         regs->ret       = uregs.scratch.ret;
 123         regs->blink     = uregs.scratch.blink;
 124         regs->fp        = uregs.scratch.fp;
 125         regs->r26       = uregs.scratch.gp;
 126         regs->r12       = uregs.scratch.r12;
 127         regs->r11       = uregs.scratch.r11;
 128         regs->r10       = uregs.scratch.r10;
 129         regs->r9        = uregs.scratch.r9;
 130         regs->r8        = uregs.scratch.r8;
 131         regs->r7        = uregs.scratch.r7;
 132         regs->r6        = uregs.scratch.r6;
 133         regs->r5        = uregs.scratch.r5;
 134         regs->r4        = uregs.scratch.r4;
 135         regs->r3        = uregs.scratch.r3;
 136         regs->r2        = uregs.scratch.r2;
 137         regs->r1        = uregs.scratch.r1;
 138         regs->r0        = uregs.scratch.r0;
 139         regs->sp        = uregs.scratch.sp;
 140
 141         return err;
 142 }
 143
 144 static inline int is_do_ss_needed(unsigned int magic)
 145 {
 146         if (MAGIC_SIGALTSTK == magic)
 147                 return 1;
 148         else
 149                 return 0;
 150 }
 151
 152 SYSCALL_DEFINE0(rt_sigreturn)
 153 {
 154         struct rt_sigframe __user *sf;
 155         unsigned int magic;
 156         struct pt_regs *regs = current_pt_regs();
 157
 158         /* Always make any pending restarted system calls return -EINTR */
 159         current->restart_block.fn = do_no_restart_syscall;
 160
 161         /* Since we stacked the signal on a word boundary,
 162          * then 'sp' should be word aligned here.  If it's
 163          * not, then the user is trying to mess with us.
 164          */
 165         if (regs->sp & 3)
 166                 goto badframe;
 167
 168         sf = (struct rt_sigframe __force __user *)(regs->sp);
 169
 170         if (!access_ok(VERIFY_READ, sf, sizeof(*sf)))
 171                 goto badframe;
 172
 173         if (__get_user(magic, &sf->sigret_magic))
 174                 goto badframe;
 175
 176         if (unlikely(is_do_ss_needed(magic)))
 177                 if (restore_altstack(&sf->uc.uc_stack))
 178                         goto badframe;
 179
 180         if (restore_usr_regs(regs, sf))
 181                 goto badframe;
 182
 183         /* Don't restart from sigreturn */
 184         syscall_wont_restart(regs);
 185
 186         /*
 187          * Ensure that sigreturn always returns to user mode (in case the
 188          * regs saved on user stack got fudged between save and sigreturn)
 189          * Otherwise it is easy to panic the kernel with a custom
 190          * signal handler and/or restorer which clobberes the status32/ret
 191          * to return to a bogus location in kernel mode.
 192          */
 193         regs->status32 |= STATUS_U_MASK;
 194
 195         return regs->r0;
 196
 197 badframe:
 198         force_sig(SIGSEGV, current);
 199         return 0;
 200 }
 201
 202 /*
 203  * Determine which stack to use..
 204  */
 205 static inline void __user *get_sigframe(struct ksignal *ksig,
 206                                         struct pt_regs *regs,
 207                                         unsigned long framesize)
 208 {
 209         unsigned long sp = sigsp(regs->sp, ksig);
 210         void __user *frame;
 211
 212         /* No matter what happens, 'sp' must be word
 213          * aligned otherwise nasty things could happen
 214          */
 215
 216         /* ATPCS B01 mandates 8-byte alignment */
 217         frame = (void __user *)((sp - framesize) & ~7);
 218
 219         /* Check that we can actually write to the signal frame */
 220         if (!access_ok(VERIFY_WRITE, frame, framesize))
 221                 frame = NULL;
 222
 223         return frame;
 224 }
 225
 226 static int
 227 setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
 228 {
 229         struct rt_sigframe __user *sf;
 230         unsigned int magic = 0;
 231         int err = 0;
 232
 233         sf = get_sigframe(ksig, regs, sizeof(struct rt_sigframe));
 234         if (!sf)
 235                 return 1;
 236
 237         /*
 238          * w/o SA_SIGINFO, struct ucontext is partially populated (only
 239          * uc_mcontext/uc_sigmask) for kernel's normal user state preservation
 240          * during signal handler execution. This works for SA_SIGINFO as well
 241          * although the semantics are now overloaded (the same reg state can be
 242          * inspected by userland: but are they allowed to fiddle with it ?
 243          */
 244         err |= stash_usr_regs(sf, regs, set);
 245
 246         /*
 247          * SA_SIGINFO requires 3 args to signal handler:
 248          *  #1: sig-no (common to any handler)
 249          *  #2: struct siginfo
 250          *  #3: struct ucontext (completely populated)
 251          */
 252         if (unlikely(ksig->ka.sa.sa_flags & SA_SIGINFO)) {
 253                 err |= copy_siginfo_to_user(&sf->info, &ksig->info);
 254                 err |= __put_user(0, &sf->uc.uc_flags);
 255                 err |= __put_user(NULL, &sf->uc.uc_link);
 256                 err |= __save_altstack(&sf->uc.uc_stack, regs->sp);
 257
 258                 /* setup args 2 and 3 for user mode handler */
 259                 regs->r1 = (unsigned long)&sf->info;
 260                 regs->r2 = (unsigned long)&sf->uc;
 261
 262                 /*
 263                  * small optim to avoid unconditonally calling do_sigaltstack
 264                  * in sigreturn path, now that we only have rt_sigreturn
 265                  */
 266                 magic = MAGIC_SIGALTSTK;
 267         }
 268
 269         err |= __put_user(magic, &sf->sigret_magic);
 270         if (err)
 271                 return err;
 272
 273         /* #1 arg to the user Signal handler */
 274         regs->r0 = ksig->sig;
 275
 276         /* setup PC of user space signal handler */
 277         regs->ret = (unsigned long)ksig->ka.sa.sa_handler;
 278
 279         /*
 280          * handler returns using sigreturn stub provided already by userpsace
 281          * If not, nuke the process right away
 282          */
 283         if(!(ksig->ka.sa.sa_flags & SA_RESTORER))
 284                 return 1;
 285
 286         regs->blink = (unsigned long)ksig->ka.sa.sa_restorer;
 287
 288         /* User Stack for signal handler will be above the frame just carved */
 289         regs->sp = (unsigned long)sf;
 290
 291         /*
 292          * Bug 94183, Clear the DE bit, so that when signal handler
 293          * starts to run, it doesn't use BTA
 294          */
 295         regs->status32 &= ~STATUS_DE_MASK;
 296         regs->status32 |= STATUS_L_MASK;
 297
 298         return err;
 299 }
 300
 301 static void arc_restart_syscall(struct k_sigaction *ka, struct pt_regs *regs)
 302 {
 303         switch (regs->r0) {
 304         case -ERESTART_RESTARTBLOCK:
 305         case -ERESTARTNOHAND:
 306                 /*
 307                  * ERESTARTNOHAND means that the syscall should
 308                  * only be restarted if there was no handler for
 309                  * the signal, and since we only get here if there
 310                  * is a handler, we don't restart
 311                  */
 312                 regs->r0 = -EINTR;   /* ERESTART_xxx is internal */
 313                 break;
 314
 315         case -ERESTARTSYS:
 316                 /*
 317                  * ERESTARTSYS means to restart the syscall if
 318                  * there is no handler or the handler was
 319                  * registered with SA_RESTART
 320                  */
 321                 if (!(ka->sa.sa_flags & SA_RESTART)) {
 322                         regs->r0 = -EINTR;
 323                         break;
 324                 }
 325                 /* fallthrough */
 326
 327         case -ERESTARTNOINTR:
 328                 /*
 329                  * ERESTARTNOINTR means that the syscall should
 330                  * be called again after the signal handler returns.
 331                  * Setup reg state just as it was before doing the trap
 332                  * r0 has been clobbered with sys call ret code thus it
 333                  * needs to be reloaded with orig first arg to syscall
 334                  * in orig_r0. Rest of relevant reg-file:
 335                  * r8 (syscall num) and (r1 - r7) will be reset to
 336                  * their orig user space value when we ret from kernel
 337                  */
 338                 regs->r0 = regs->orig_r0;
 339                 regs->ret -= is_isa_arcv2() ? 2 : 4;
 340                 break;
 341         }
 342 }
 343
 344 /*
 345  * OK, we're invoking a handler
 346  */
 347 static void
 348 handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 349 {
 350         sigset_t *oldset = sigmask_to_save();
 351         int failed;
 352
 353         /* Set up the stack frame */
 354         failed = setup_rt_frame(ksig, oldset, regs);
 355
 356         signal_setup_done(failed, ksig, 0);
 357 }
 358
 359 void do_signal(struct pt_regs *regs)
 360 {
 361         struct ksignal ksig;
 362         int restart_scall;
 363
 364         restart_scall = in_syscall(regs) && syscall_restartable(regs);
 365
 366         if (get_signal(&ksig)) {
 367                 if (restart_scall) {
 368                         arc_restart_syscall(&ksig.ka, regs);
 369                         syscall_wont_restart(regs);     /* No more restarts */
 370                 }
 371                 handle_signal(&ksig, regs);
 372                 return;
 373         }
 374
 375         if (restart_scall) {
 376                 /* No handler for syscall: restart it */
 377                 if (regs->r0 == -ERESTARTNOHAND ||
 378                     regs->r0 == -ERESTARTSYS || regs->r0 == -ERESTARTNOINTR) {
 379                         regs->r0 = regs->orig_r0;
 380                         regs->ret -= is_isa_arcv2() ? 2 : 4;
 381                 } else if (regs->r0 == -ERESTART_RESTARTBLOCK) {
 382                         regs->r8 = __NR_restart_syscall;
 383                         regs->ret -= is_isa_arcv2() ? 2 : 4;
 384                 }
 385                 syscall_wont_restart(regs);     /* No more restarts */
 386         }
 387
 388         /* If there's no signal to deliver, restore the saved sigmask back */
 389         restore_saved_sigmask();
 390 }
 391
 392 void do_notify_resume(struct pt_regs *regs)
 393 {
 394         /*
 395          * ASM glue gaurantees that this is only called when returning to
 396          * user mode
 397          */
 398         if (test_and_clear_thread_flag(TIF_NOTIFY_RESUME))
 399                 tracehook_notify_resume(regs);
 400 }