linux/arch/arc/kernel/signal.c
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   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
  57struct rt_sigframe {
  58        struct siginfo info;
  59        struct ucontext uc;
  60#define MAGIC_SIGALTSTK         0x07302004
  61        unsigned int sigret_magic;
  62};
  63
  64static int save_arcv2_regs(struct sigcontext *mctx, struct pt_regs *regs)
  65{
  66        int err = 0;
  67#ifndef CONFIG_ISA_ARCOMPACT
  68        struct user_regs_arcv2 v2abi;
  69
  70        v2abi.r30 = regs->r30;
  71#ifdef CONFIG_ARC_HAS_ACCL_REGS
  72        v2abi.r58 = regs->r58;
  73        v2abi.r59 = regs->r59;
  74#else
  75        v2abi.r58 = v2abi.r59 = 0;
  76#endif
  77        err = __copy_to_user(&mctx->v2abi, &v2abi, sizeof(v2abi));
  78#endif
  79        return err;
  80}
  81
  82static int restore_arcv2_regs(struct sigcontext *mctx, struct pt_regs *regs)
  83{
  84        int err = 0;
  85#ifndef CONFIG_ISA_ARCOMPACT
  86        struct user_regs_arcv2 v2abi;
  87
  88        err = __copy_from_user(&v2abi, &mctx->v2abi, sizeof(v2abi));
  89
  90        regs->r30 = v2abi.r30;
  91#ifdef CONFIG_ARC_HAS_ACCL_REGS
  92        regs->r58 = v2abi.r58;
  93        regs->r59 = v2abi.r59;
  94#endif
  95#endif
  96        return err;
  97}
  98
  99static int
 100stash_usr_regs(struct rt_sigframe __user *sf, struct pt_regs *regs,
 101               sigset_t *set)
 102{
 103        int err;
 104        struct user_regs_struct uregs;
 105
 106        uregs.scratch.bta       = regs->bta;
 107        uregs.scratch.lp_start  = regs->lp_start;
 108        uregs.scratch.lp_end    = regs->lp_end;
 109        uregs.scratch.lp_count  = regs->lp_count;
 110        uregs.scratch.status32  = regs->status32;
 111        uregs.scratch.ret       = regs->ret;
 112        uregs.scratch.blink     = regs->blink;
 113        uregs.scratch.fp        = regs->fp;
 114        uregs.scratch.gp        = regs->r26;
 115        uregs.scratch.r12       = regs->r12;
 116        uregs.scratch.r11       = regs->r11;
 117        uregs.scratch.r10       = regs->r10;
 118        uregs.scratch.r9        = regs->r9;
 119        uregs.scratch.r8        = regs->r8;
 120        uregs.scratch.r7        = regs->r7;
 121        uregs.scratch.r6        = regs->r6;
 122        uregs.scratch.r5        = regs->r5;
 123        uregs.scratch.r4        = regs->r4;
 124        uregs.scratch.r3        = regs->r3;
 125        uregs.scratch.r2        = regs->r2;
 126        uregs.scratch.r1        = regs->r1;
 127        uregs.scratch.r0        = regs->r0;
 128        uregs.scratch.sp        = regs->sp;
 129
 130        err = __copy_to_user(&(sf->uc.uc_mcontext.regs.scratch), &uregs.scratch,
 131                             sizeof(sf->uc.uc_mcontext.regs.scratch));
 132
 133        if (is_isa_arcv2())
 134                err |= save_arcv2_regs(&(sf->uc.uc_mcontext), regs);
 135
 136        err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(sigset_t));
 137
 138        return err ? -EFAULT : 0;
 139}
 140
 141static int restore_usr_regs(struct pt_regs *regs, struct rt_sigframe __user *sf)
 142{
 143        sigset_t set;
 144        int err;
 145        struct user_regs_struct uregs;
 146
 147        err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
 148        err |= __copy_from_user(&uregs.scratch,
 149                                &(sf->uc.uc_mcontext.regs.scratch),
 150                                sizeof(sf->uc.uc_mcontext.regs.scratch));
 151
 152        if (is_isa_arcv2())
 153                err |= restore_arcv2_regs(&(sf->uc.uc_mcontext), regs);
 154
 155        if (err)
 156                return -EFAULT;
 157
 158        set_current_blocked(&set);
 159        regs->bta       = uregs.scratch.bta;
 160        regs->lp_start  = uregs.scratch.lp_start;
 161        regs->lp_end    = uregs.scratch.lp_end;
 162        regs->lp_count  = uregs.scratch.lp_count;
 163        regs->status32  = uregs.scratch.status32;
 164        regs->ret       = uregs.scratch.ret;
 165        regs->blink     = uregs.scratch.blink;
 166        regs->fp        = uregs.scratch.fp;
 167        regs->r26       = uregs.scratch.gp;
 168        regs->r12       = uregs.scratch.r12;
 169        regs->r11       = uregs.scratch.r11;
 170        regs->r10       = uregs.scratch.r10;
 171        regs->r9        = uregs.scratch.r9;
 172        regs->r8        = uregs.scratch.r8;
 173        regs->r7        = uregs.scratch.r7;
 174        regs->r6        = uregs.scratch.r6;
 175        regs->r5        = uregs.scratch.r5;
 176        regs->r4        = uregs.scratch.r4;
 177        regs->r3        = uregs.scratch.r3;
 178        regs->r2        = uregs.scratch.r2;
 179        regs->r1        = uregs.scratch.r1;
 180        regs->r0        = uregs.scratch.r0;
 181        regs->sp        = uregs.scratch.sp;
 182
 183        return 0;
 184}
 185
 186static inline int is_do_ss_needed(unsigned int magic)
 187{
 188        if (MAGIC_SIGALTSTK == magic)
 189                return 1;
 190        else
 191                return 0;
 192}
 193
 194SYSCALL_DEFINE0(rt_sigreturn)
 195{
 196        struct rt_sigframe __user *sf;
 197        unsigned int magic;
 198        struct pt_regs *regs = current_pt_regs();
 199
 200        /* Always make any pending restarted system calls return -EINTR */
 201        current->restart_block.fn = do_no_restart_syscall;
 202
 203        /* Since we stacked the signal on a word boundary,
 204         * then 'sp' should be word aligned here.  If it's
 205         * not, then the user is trying to mess with us.
 206         */
 207        if (regs->sp & 3)
 208                goto badframe;
 209
 210        sf = (struct rt_sigframe __force __user *)(regs->sp);
 211
 212        if (!access_ok(sf, sizeof(*sf)))
 213                goto badframe;
 214
 215        if (__get_user(magic, &sf->sigret_magic))
 216                goto badframe;
 217
 218        if (unlikely(is_do_ss_needed(magic)))
 219                if (restore_altstack(&sf->uc.uc_stack))
 220                        goto badframe;
 221
 222        if (restore_usr_regs(regs, sf))
 223                goto badframe;
 224
 225        /* Don't restart from sigreturn */
 226        syscall_wont_restart(regs);
 227
 228        /*
 229         * Ensure that sigreturn always returns to user mode (in case the
 230         * regs saved on user stack got fudged between save and sigreturn)
 231         * Otherwise it is easy to panic the kernel with a custom
 232         * signal handler and/or restorer which clobberes the status32/ret
 233         * to return to a bogus location in kernel mode.
 234         */
 235        regs->status32 |= STATUS_U_MASK;
 236
 237        return regs->r0;
 238
 239badframe:
 240        force_sig(SIGSEGV);
 241        return 0;
 242}
 243
 244/*
 245 * Determine which stack to use..
 246 */
 247static inline void __user *get_sigframe(struct ksignal *ksig,
 248                                        struct pt_regs *regs,
 249                                        unsigned long framesize)
 250{
 251        unsigned long sp = sigsp(regs->sp, ksig);
 252        void __user *frame;
 253
 254        /* No matter what happens, 'sp' must be word
 255         * aligned otherwise nasty things could happen
 256         */
 257
 258        /* ATPCS B01 mandates 8-byte alignment */
 259        frame = (void __user *)((sp - framesize) & ~7);
 260
 261        /* Check that we can actually write to the signal frame */
 262        if (!access_ok(frame, framesize))
 263                frame = NULL;
 264
 265        return frame;
 266}
 267
 268static int
 269setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
 270{
 271        struct rt_sigframe __user *sf;
 272        unsigned int magic = 0;
 273        int err = 0;
 274
 275        sf = get_sigframe(ksig, regs, sizeof(struct rt_sigframe));
 276        if (!sf)
 277                return 1;
 278
 279        /*
 280         * w/o SA_SIGINFO, struct ucontext is partially populated (only
 281         * uc_mcontext/uc_sigmask) for kernel's normal user state preservation
 282         * during signal handler execution. This works for SA_SIGINFO as well
 283         * although the semantics are now overloaded (the same reg state can be
 284         * inspected by userland: but are they allowed to fiddle with it ?
 285         */
 286        err |= stash_usr_regs(sf, regs, set);
 287
 288        /*
 289         * SA_SIGINFO requires 3 args to signal handler:
 290         *  #1: sig-no (common to any handler)
 291         *  #2: struct siginfo
 292         *  #3: struct ucontext (completely populated)
 293         */
 294        if (unlikely(ksig->ka.sa.sa_flags & SA_SIGINFO)) {
 295                err |= copy_siginfo_to_user(&sf->info, &ksig->info);
 296                err |= __put_user(0, &sf->uc.uc_flags);
 297                err |= __put_user(NULL, &sf->uc.uc_link);
 298                err |= __save_altstack(&sf->uc.uc_stack, regs->sp);
 299
 300                /* setup args 2 and 3 for user mode handler */
 301                regs->r1 = (unsigned long)&sf->info;
 302                regs->r2 = (unsigned long)&sf->uc;
 303
 304                /*
 305                 * small optim to avoid unconditionally calling do_sigaltstack
 306                 * in sigreturn path, now that we only have rt_sigreturn
 307                 */
 308                magic = MAGIC_SIGALTSTK;
 309        }
 310
 311        err |= __put_user(magic, &sf->sigret_magic);
 312        if (err)
 313                return err;
 314
 315        /* #1 arg to the user Signal handler */
 316        regs->r0 = ksig->sig;
 317
 318        /* setup PC of user space signal handler */
 319        regs->ret = (unsigned long)ksig->ka.sa.sa_handler;
 320
 321        /*
 322         * handler returns using sigreturn stub provided already by userpsace
 323         * If not, nuke the process right away
 324         */
 325        if(!(ksig->ka.sa.sa_flags & SA_RESTORER))
 326                return 1;
 327
 328        regs->blink = (unsigned long)ksig->ka.sa.sa_restorer;
 329
 330        /* User Stack for signal handler will be above the frame just carved */
 331        regs->sp = (unsigned long)sf;
 332
 333        /*
 334         * Bug 94183, Clear the DE bit, so that when signal handler
 335         * starts to run, it doesn't use BTA
 336         */
 337        regs->status32 &= ~STATUS_DE_MASK;
 338        regs->status32 |= STATUS_L_MASK;
 339
 340        return err;
 341}
 342
 343static void arc_restart_syscall(struct k_sigaction *ka, struct pt_regs *regs)
 344{
 345        switch (regs->r0) {
 346        case -ERESTART_RESTARTBLOCK:
 347        case -ERESTARTNOHAND:
 348                /*
 349                 * ERESTARTNOHAND means that the syscall should
 350                 * only be restarted if there was no handler for
 351                 * the signal, and since we only get here if there
 352                 * is a handler, we don't restart
 353                 */
 354                regs->r0 = -EINTR;   /* ERESTART_xxx is internal */
 355                break;
 356
 357        case -ERESTARTSYS:
 358                /*
 359                 * ERESTARTSYS means to restart the syscall if
 360                 * there is no handler or the handler was
 361                 * registered with SA_RESTART
 362                 */
 363                if (!(ka->sa.sa_flags & SA_RESTART)) {
 364                        regs->r0 = -EINTR;
 365                        break;
 366                }
 367                fallthrough;
 368
 369        case -ERESTARTNOINTR:
 370                /*
 371                 * ERESTARTNOINTR means that the syscall should
 372                 * be called again after the signal handler returns.
 373                 * Setup reg state just as it was before doing the trap
 374                 * r0 has been clobbered with sys call ret code thus it
 375                 * needs to be reloaded with orig first arg to syscall
 376                 * in orig_r0. Rest of relevant reg-file:
 377                 * r8 (syscall num) and (r1 - r7) will be reset to
 378                 * their orig user space value when we ret from kernel
 379                 */
 380                regs->r0 = regs->orig_r0;
 381                regs->ret -= is_isa_arcv2() ? 2 : 4;
 382                break;
 383        }
 384}
 385
 386/*
 387 * OK, we're invoking a handler
 388 */
 389static void
 390handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 391{
 392        sigset_t *oldset = sigmask_to_save();
 393        int failed;
 394
 395        /* Set up the stack frame */
 396        failed = setup_rt_frame(ksig, oldset, regs);
 397
 398        signal_setup_done(failed, ksig, 0);
 399}
 400
 401void do_signal(struct pt_regs *regs)
 402{
 403        struct ksignal ksig;
 404        int restart_scall;
 405
 406        restart_scall = in_syscall(regs) && syscall_restartable(regs);
 407
 408        if (test_thread_flag(TIF_SIGPENDING) && get_signal(&ksig)) {
 409                if (restart_scall) {
 410                        arc_restart_syscall(&ksig.ka, regs);
 411                        syscall_wont_restart(regs);     /* No more restarts */
 412                }
 413                handle_signal(&ksig, regs);
 414                return;
 415        }
 416
 417        if (restart_scall) {
 418                /* No handler for syscall: restart it */
 419                if (regs->r0 == -ERESTARTNOHAND ||
 420                    regs->r0 == -ERESTARTSYS || regs->r0 == -ERESTARTNOINTR) {
 421                        regs->r0 = regs->orig_r0;
 422                        regs->ret -= is_isa_arcv2() ? 2 : 4;
 423                } else if (regs->r0 == -ERESTART_RESTARTBLOCK) {
 424                        regs->r8 = __NR_restart_syscall;
 425                        regs->ret -= is_isa_arcv2() ? 2 : 4;
 426                }
 427                syscall_wont_restart(regs);     /* No more restarts */
 428        }
 429
 430        /* If there's no signal to deliver, restore the saved sigmask back */
 431        restore_saved_sigmask();
 432}
 433
 434void do_notify_resume(struct pt_regs *regs)
 435{
 436        /*
 437         * ASM glue guarantees that this is only called when returning to
 438         * user mode
 439         */
 440        if (test_thread_flag(TIF_NOTIFY_RESUME))
 441                tracehook_notify_resume(regs);
 442}
 443