signal.c

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/*
 * Copyright (C) 2003, Axis Communications AB.
 */

#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/wait.h>
#include <linux/ptrace.h>
#include <linux/unistd.h>
#include <linux/stddef.h>
#include <linux/syscalls.h>
#include <linux/vmalloc.h>

#include <asm/io.h>
#include <asm/processor.h>
#include <asm/ucontext.h>
#include <asm/uaccess.h>
#include <arch/ptrace.h>
#include <arch/hwregs/cpu_vect.h>

extern unsigned long cris_signal_return_page;

/*
 * A syscall in CRIS is really a "break 13" instruction, which is 2
 * bytes. The registers is manipulated so upon return the instruction
 * will be executed again.
 *
 * This relies on that PC points to the instruction after the break call.
 */
#define RESTART_CRIS_SYS(regs) regs->r10 = regs->orig_r10; regs->erp -= 2;

/* Signal frames. */
struct signal_frame {
    struct sigcontext sc;
    unsigned long extramask[_NSIG_WORDS - 1];
    unsigned char retcode[8];   /* Trampoline code. */
};

struct rt_signal_frame {
    struct siginfo *pinfo;
    void *puc;
    struct siginfo info;
    struct ucontext uc;
    unsigned char retcode[8];   /* Trampoline code. */
};

void do_signal(int restart, struct pt_regs *regs);
void keep_debug_flags(unsigned long oldccs, unsigned long oldspc,
              struct pt_regs *regs);
/*
 * Swap in the new signal mask, and wait for a signal. Define some
 * dummy arguments to be able to reach the regs argument.
 */
int
sys_sigsuspend(old_sigset_t mask)
{
    sigset_t blocked;
    siginitset(&blocked, mask);
    return sigsuspend(&blocked);
}

int
sys_sigaction(int signal, const struct old_sigaction *act,
          struct old_sigaction *oact)
{
    int retval;
    struct k_sigaction newk;
    struct k_sigaction oldk;

    if (act) {
        old_sigset_t mask;

        if (!access_ok(VERIFY_READ, act, sizeof(*act)) ||
            __get_user(newk.sa.sa_handler, &act->sa_handler) ||
            __get_user(newk.sa.sa_restorer, &act->sa_restorer) ||
            __get_user(newk.sa.sa_flags, &act->sa_flags) ||
            __get_user(mask, &act->sa_mask))
            return -EFAULT;

        siginitset(&newk.sa.sa_mask, mask);
    }

    retval = do_sigaction(signal, act ? &newk : NULL, oact ? &oldk : NULL);

    if (!retval && oact) {
        if (!access_ok(VERIFY_WRITE, oact, sizeof(*oact)) ||
            __put_user(oldk.sa.sa_handler, &oact->sa_handler) ||
            __put_user(oldk.sa.sa_restorer, &oact->sa_restorer) ||
            __put_user(oldk.sa.sa_flags, &oact->sa_flags) ||
            __put_user(oldk.sa.sa_mask.sig[0], &oact->sa_mask))
            return -EFAULT;

    }

    return retval;
}

int
sys_sigaltstack(const stack_t __user *uss, stack_t __user *uoss)
{
    return do_sigaltstack(uss, uoss, rdusp());
}

static int
restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
{
    unsigned int err = 0;
    unsigned long old_usp;

        /* Always make any pending restarted system calls return -EINTR */
    current_thread_info()->restart_block.fn = do_no_restart_syscall;

    /*
     * Restore the registers from &sc->regs. sc is already checked
     * for VERIFY_READ since the signal_frame was previously
     * checked in sys_sigreturn().
     */
    if (__copy_from_user(regs, sc, sizeof(struct pt_regs)))
        goto badframe;

    /* Make that the user-mode flag is set. */
    regs->ccs |= (1 << (U_CCS_BITNR + CCS_SHIFT));

    /* Restore the old USP. */
    err |= __get_user(old_usp, &sc->usp);
    wrusp(old_usp);

    return err;

badframe:
    return 1;
}

/* Define some dummy arguments to be able to reach the regs argument. */
asmlinkage int
sys_sigreturn(long r10, long r11, long r12, long r13, long mof, long srp,
          struct pt_regs *regs)
{
    sigset_t set;
    struct signal_frame __user *frame;
    unsigned long oldspc = regs->spc;
    unsigned long oldccs = regs->ccs;

    frame = (struct signal_frame *) rdusp();

    /*
     * Since the signal is stacked on a dword boundary, the frame
     * should be dword aligned here as well. It it's not, then the
     * user is trying some funny business.
     */
    if (((long)frame) & 3)
        goto badframe;

    if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
        goto badframe;

    if (__get_user(set.sig[0], &frame->sc.oldmask) ||
        (_NSIG_WORDS > 1 && __copy_from_user(&set.sig[1],
                         frame->extramask,
                         sizeof(frame->extramask))))
        goto badframe;

    set_current_blocked(&set);

    if (restore_sigcontext(regs, &frame->sc))
        goto badframe;

    keep_debug_flags(oldccs, oldspc, regs);

    return regs->r10;

badframe:
    force_sig(SIGSEGV, current);
    return 0;
}

/* Define some dummy variables to be able to reach the regs argument. */
asmlinkage int
sys_rt_sigreturn(long r10, long r11, long r12, long r13, long mof, long srp,
         struct pt_regs *regs)
{
    sigset_t set;
    struct rt_signal_frame __user *frame;
    unsigned long oldspc = regs->spc;
    unsigned long oldccs = regs->ccs;

    frame = (struct rt_signal_frame *) rdusp();

    /*
     * Since the signal is stacked on a dword boundary, the frame
     * should be dword aligned here as well. It it's not, then the
     * user is trying some funny business.
     */
    if (((long)frame) & 3)
        goto badframe;

    if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
        goto badframe;

    if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
        goto badframe;

    set_current_blocked(&set);

    if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
        goto badframe;

    if (do_sigaltstack(&frame->uc.uc_stack, NULL, rdusp()) == -EFAULT)
        goto badframe;

    keep_debug_flags(oldccs, oldspc, regs);

    return regs->r10;

badframe:
    force_sig(SIGSEGV, current);
    return 0;
}

/* Setup a signal frame. */
static int
setup_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs,
         unsigned long mask)
{
    int err;
    unsigned long usp;

    err = 0;
    usp = rdusp();

    /*
     * Copy the registers. They are located first in sc, so it's
     * possible to use sc directly.
     */
    err |= __copy_to_user(sc, regs, sizeof(struct pt_regs));

    err |= __put_user(mask, &sc->oldmask);
    err |= __put_user(usp, &sc->usp);

    return err;
}

/* Figure out where to put the new signal frame - usually on the stack. */
static inline void __user *
get_sigframe(struct k_sigaction *ka, struct pt_regs * regs, size_t frame_size)
{
    unsigned long sp;

    sp = rdusp();

    /* This is the X/Open sanctioned signal stack switching. */
    if (ka->sa.sa_flags & SA_ONSTACK) {
        if (!on_sig_stack(sp))
            sp = current->sas_ss_sp + current->sas_ss_size;
    }

    /* Make sure the frame is dword-aligned. */
    sp &= ~3;

    return (void __user *)(sp - frame_size);
}

/* Grab and setup a signal frame.
 *
 * Basically a lot of state-info is stacked, and arranged for the
 * user-mode program to return to the kernel using either a trampiline
 * which performs the syscall sigreturn(), or a provided user-mode
 * trampoline.
  */
static int
setup_frame(int sig, struct k_sigaction *ka,  sigset_t *set,
        struct pt_regs * regs)
{
    int err;
    unsigned long return_ip;
    struct signal_frame __user *frame;

    err = 0;
    frame = get_sigframe(ka, regs, sizeof(*frame));

    if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
        goto give_sigsegv;

    err |= setup_sigcontext(&frame->sc, regs, set->sig[0]);

    if (err)
        goto give_sigsegv;

    if (_NSIG_WORDS > 1) {
        err |= __copy_to_user(frame->extramask, &set->sig[1],
                      sizeof(frame->extramask));
    }

    if (err)
        goto give_sigsegv;

    /*
     * Set up to return from user-space. If provided, use a stub
     * already located in user-space.
     */
    if (ka->sa.sa_flags & SA_RESTORER) {
        return_ip = (unsigned long)ka->sa.sa_restorer;
    } else {
        /* Trampoline - the desired return ip is in the signal return page. */
        return_ip = cris_signal_return_page;

        /*
         * This is movu.w __NR_sigreturn, r9; break 13;
         *
         * WE DO NOT USE IT ANY MORE! It's only left here for historical
         * reasons and because gdb uses it as a signature to notice
         * signal handler stack frames.
         */
        err |= __put_user(0x9c5f,         (short __user*)(frame->retcode+0));
        err |= __put_user(__NR_sigreturn, (short __user*)(frame->retcode+2));
        err |= __put_user(0xe93d,         (short __user*)(frame->retcode+4));
    }

    if (err)
        goto give_sigsegv;

    /*
     * Set up registers for signal handler.
     *
     * Where the code enters now.
     * Where the code enter later.
     * First argument, signo.
     */
    regs->erp = (unsigned long) ka->sa.sa_handler;
    regs->srp = return_ip;
    regs->r10 = sig;

    /* Actually move the USP to reflect the stacked frame. */
    wrusp((unsigned long)frame);

    return 0;

give_sigsegv:
    force_sigsegv(sig, current);
    return -EFAULT;
}

static int
setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
           sigset_t *set, struct pt_regs * regs)
{
    int err;
    unsigned long return_ip;
    struct rt_signal_frame __user *frame;

    err = 0;
    frame = get_sigframe(ka, regs, sizeof(*frame));

    if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
        goto give_sigsegv;

    /* TODO: what is the current->exec_domain stuff and invmap ? */

    err |= __put_user(&frame->info, &frame->pinfo);
    err |= __put_user(&frame->uc, &frame->puc);
    err |= copy_siginfo_to_user(&frame->info, info);

    if (err)
        goto give_sigsegv;

    /* Clear all the bits of the ucontext we don't use.  */
    err |= __clear_user(&frame->uc, offsetof(struct ucontext, uc_mcontext));
    err |= setup_sigcontext(&frame->uc.uc_mcontext, regs, set->sig[0]);
    err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));

    if (err)
        goto give_sigsegv;

    /*
     * Set up to return from user-space. If provided, use a stub
     * already located in user-space.
     */
    if (ka->sa.sa_flags & SA_RESTORER) {
        return_ip = (unsigned long) ka->sa.sa_restorer;
    } else {
        /* Trampoline - the desired return ip is in the signal return page. */
        return_ip = cris_signal_return_page + 6;

        /*
         * This is movu.w __NR_rt_sigreturn, r9; break 13;
         *
         * WE DO NOT USE IT ANY MORE! It's only left here for historical
         * reasons and because gdb uses it as a signature to notice
         * signal handler stack frames.
         */
        err |= __put_user(0x9c5f, (short __user*)(frame->retcode+0));

        err |= __put_user(__NR_rt_sigreturn,
                  (short __user*)(frame->retcode+2));

        err |= __put_user(0xe93d, (short __user*)(frame->retcode+4));
    }

    if (err)
        goto give_sigsegv;

    /*
     * Set up registers for signal handler.
     *
     * Where the code enters now.
     * Where the code enters later.
     * First argument is signo.
     * Second argument is (siginfo_t *).
     * Third argument is unused.
     */
    regs->erp = (unsigned long) ka->sa.sa_handler;
    regs->srp = return_ip;
    regs->r10 = sig;
    regs->r11 = (unsigned long) &frame->info;
    regs->r12 = 0;

    /* Actually move the usp to reflect the stacked frame. */
    wrusp((unsigned long)frame);

    return 0;

give_sigsegv:
    force_sigsegv(sig, current);
    return -EFAULT;
}

/* Invoke a signal handler to, well, handle the signal. */
static inline void
handle_signal(int canrestart, unsigned long sig,
          siginfo_t *info, struct k_sigaction *ka,
              struct pt_regs * regs)
{
    sigset_t *oldset = sigmask_to_save();
    int ret;

    /* Check if this got called from a system call. */
    if (canrestart) {
        /* If so, check system call restarting. */
        switch (regs->r10) {
            case -ERESTART_RESTARTBLOCK:
            case -ERESTARTNOHAND:
                /*
                 * This means that the syscall should
                 * only be restarted if there was no
                 * handler for the signal, and since
                 * this point isn't reached unless
                 * there is a handler, there's no need
                 * to restart.
                 */
                regs->r10 = -EINTR;
                break;

                        case -ERESTARTSYS:
                /*
                 * This means restart the syscall if
                                 * there is no handler, or the handler
                                 * was registered with SA_RESTART.
                 */
                if (!(ka->sa.sa_flags & SA_RESTART)) {
                    regs->r10 = -EINTR;
                    break;
                }

                /* Fall through. */

            case -ERESTARTNOINTR:
                /*
                 * This means that the syscall should
                                 * be called again after the signal
                                 * handler returns.
                 */
                RESTART_CRIS_SYS(regs);
                break;
                }
        }

    /* Set up the stack frame. */
    if (ka->sa.sa_flags & SA_SIGINFO)
        ret = setup_rt_frame(sig, ka, info, oldset, regs);
    else
        ret = setup_frame(sig, ka, oldset, regs);

    if (ret == 0)
        signal_delivered(sig, info, ka, regs, 0);
}

/*
 * Note that 'init' is a special process: it doesn't get signals it doesn't
 * want to handle. Thus you cannot kill init even with a SIGKILL even by
 * mistake.
 *
 * Also note that the regs structure given here as an argument, is the latest
 * pushed pt_regs. It may or may not be the same as the first pushed registers
 * when the initial usermode->kernelmode transition took place. Therefore
 * we can use user_mode(regs) to see if we came directly from kernel or user
 * mode below.
 */
void
do_signal(int canrestart, struct pt_regs *regs)
{
    int signr;
    siginfo_t info;
        struct k_sigaction ka;

    /*
     * The common case should go fast, which is why this point is
     * reached from kernel-mode. If that's the case, just return
     * without doing anything.
     */
    if (!user_mode(regs))
        return;

    signr = get_signal_to_deliver(&info, &ka, regs, NULL);

    if (signr > 0) {
        /* Whee!  Actually deliver the signal.  */
        handle_signal(canrestart, signr, &info, &ka, regs);
        return;
    }

    /* Got here from a system call? */
    if (canrestart) {
        /* Restart the system call - no handlers present. */
        if (regs->r10 == -ERESTARTNOHAND ||
            regs->r10 == -ERESTARTSYS ||
            regs->r10 == -ERESTARTNOINTR) {
            RESTART_CRIS_SYS(regs);
        }

        if (regs->r10 == -ERESTART_RESTARTBLOCK){
            regs->r9 = __NR_restart_syscall;
            regs->erp -= 2;
        }
    }

    /* if there's no signal to deliver, we just put the saved sigmask
     * back */
    restore_saved_sigmask();
}

asmlinkage void
ugdb_trap_user(struct thread_info *ti, int sig)
{
    if (((user_regs(ti)->exs & 0xff00) >> 8) != SINGLE_STEP_INTR_VECT) {
        /* Zero single-step PC if the reason we stopped wasn't a single
           step exception. This is to avoid relying on it when it isn't
           reliable. */
        user_regs(ti)->spc = 0;
    }
    /* FIXME: Filter out false h/w breakpoint hits (i.e. EDA
       not within any configured h/w breakpoint range). Synchronize with
       what already exists for kernel debugging.  */
    if (((user_regs(ti)->exs & 0xff00) >> 8) == BREAK_8_INTR_VECT) {
        /* Break 8: subtract 2 from ERP unless in a delay slot. */
        if (!(user_regs(ti)->erp & 0x1))
            user_regs(ti)->erp -= 2;
    }
    sys_kill(ti->task->pid, sig);
}

void
keep_debug_flags(unsigned long oldccs, unsigned long oldspc,
         struct pt_regs *regs)
{
    if (oldccs & (1 << Q_CCS_BITNR)) {
        /* Pending single step due to single-stepping the break 13
           in the signal trampoline: keep the Q flag. */
        regs->ccs |= (1 << Q_CCS_BITNR);
        /* S flag should be set - complain if it's not. */
        if (!(oldccs & (1 << (S_CCS_BITNR + CCS_SHIFT)))) {
            printk("Q flag but no S flag?");
        }
        regs->ccs |= (1 << (S_CCS_BITNR + CCS_SHIFT));
        /* Assume the SPC is valid and interesting. */
        regs->spc = oldspc;

    } else if (oldccs & (1 << (S_CCS_BITNR + CCS_SHIFT))) {
        /* If a h/w bp was set in the signal handler we need
           to keep the S flag. */
        regs->ccs |= (1 << (S_CCS_BITNR + CCS_SHIFT));
        /* Don't keep the old SPC though; if we got here due to
           a single-step, the Q flag should have been set. */
    } else if (regs->spc) {
        /* If we were single-stepping *before* the signal was taken,
           we don't want to restore that state now, because GDB will
           have forgotten all about it. */
        regs->spc = 0;
        regs->ccs &= ~(1 << (S_CCS_BITNR + CCS_SHIFT));
    }
}

/* Set up the trampolines on the signal return page. */
int __init
cris_init_signal(void)
{
    u16* data = kmalloc(PAGE_SIZE, GFP_KERNEL);

    /* This is movu.w __NR_sigreturn, r9; break 13; */
    data[0] = 0x9c5f;
    data[1] = __NR_sigreturn;
    data[2] = 0xe93d;
    /* This is movu.w __NR_rt_sigreturn, r9; break 13; */
    data[3] = 0x9c5f;
    data[4] = __NR_rt_sigreturn;
    data[5] = 0xe93d;

    /* Map to userspace with appropriate permissions (no write access...) */
    cris_signal_return_page = (unsigned long)
          __ioremap_prot(virt_to_phys(data), PAGE_SIZE, PAGE_SIGNAL_TRAMPOLINE);

    return 0;
}

__initcall(cris_init_signal);