// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/arch/cris/kernel/signal.c
 *
 *  Based on arch/i386/kernel/signal.c by
 *     Copyright (C) 1991, 1992  Linus Torvalds
 *     1997-11-28  Modified for POSIX.1b signals by Richard Henderson *
 *
 *  Ideas also taken from arch/arm.
 *
 *  Copyright (C) 2000-2007 Axis Communications AB
 *
 *  Authors:  Bjorn Wesen (bjornw@axis.com)
 *
 */

#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/mm.h>
#include <linux/smp.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 <asm/processor.h>
#include <asm/ucontext.h>
#include <linux/uaccess.h>
#include <arch/system.h>

#define DEBUG_SIG 0

/* a syscall in Linux/CRIS is a break 13 instruction which is 2 bytes */
/* manipulate regs so that upon return, it will be re-executed */

/* We rely on that pc points to the instruction after "break 13", so the
 * library must never do strange things like putting it in a delay slot.
 */
#define RESTART_CRIS_SYS(regs) regs->r10 = regs->orig_r10; regs->irp -= 2;

void do_signal(int canrestart, struct pt_regs *regs);

/*
 * Do a signal return; undo the signal stack.
 */

struct sigframe {
        struct sigcontext sc;
        unsigned long extramask[_NSIG_WORDS-1];
        unsigned char retcode[8];  /* trampoline code */
};

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


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->restart_block.fn = do_no_restart_syscall;

        /* restore the regs from &sc->regs (same as sc, since regs is first)
         * (sc is already checked for VERIFY_READ since the sigframe was
         *  checked in sys_sigreturn previously)
         */

        if (__copy_from_user(regs, sc, sizeof(struct pt_regs)))
                goto badframe;

        /* make sure the U-flag is set so user-mode cannot fool us */

        regs->dccr |= 1 << 8;

        /* restore the old USP as it was before we stacked the sc etc.
         * (we cannot just pop the sigcontext since we aligned the sp and
         *  stuff after pushing it)
         */

        err |= __get_user(old_usp, &sc->usp);

        wrusp(old_usp);

        /* TODO: the other ports use regs->orig_XX to disable syscall checks
         * after this completes, but we don't use that mechanism. maybe we can
         * use it now ?
         */

        return err;

badframe:
        return 1;
}

asmlinkage int sys_sigreturn(void)
{
        struct pt_regs *regs = current_pt_regs();
        struct sigframe __user *frame = (struct sigframe *)rdusp();
        sigset_t set;

        /*
         * Since we stacked the signal on a dword boundary,
         * then frame should be dword aligned here.  If it's
         * not, then the user is trying to mess with us.
         */
        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;

        /* TODO: SIGTRAP when single-stepping as in arm ? */

        return regs->r10;

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

asmlinkage int sys_rt_sigreturn(void)
{
        struct pt_regs *regs = current_pt_regs();
        struct rt_sigframe __user *frame = (struct rt_sigframe *)rdusp();
        sigset_t set;

        /*
         * Since we stacked the signal on a dword boundary,
         * then frame should be dword aligned here.  If it's
         * not, then the user is trying to mess with us.
         */
        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 (restore_altstack(&frame->uc.uc_stack))
                goto badframe;

        return regs->r10;

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

/*
 * Set up a signal frame.
 */

static int setup_sigcontext(struct sigcontext __user *sc,
        struct pt_regs *regs, unsigned long mask)
{
        int err = 0;
        unsigned long usp = rdusp();

        /* copy the regs. they are first in sc so we can use sc directly */

        err |= __copy_to_user(sc, regs, sizeof(struct pt_regs));

        /* Set the frametype to CRIS_FRAME_NORMAL for the execution of
           the signal handler. The frametype will be restored to its previous
           value in restore_sigcontext. */
        regs->frametype = CRIS_FRAME_NORMAL;

        /* then some other stuff */

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

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

        return err;
}

/* Figure out where we want to put the new signal frame
 * - usually on the stack. */

static inline void __user *
get_sigframe(struct ksignal *ksig, size_t frame_size)
{
        unsigned long sp = sigsp(rdusp(), ksig);

        /* make sure the frame is dword-aligned */

        sp &= ~3;

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

/* grab and setup a signal frame.
 *
 * basically we stack a lot of state info, and arrange for the
 * user-mode program to return to the kernel using either a
 * trampoline which performs the syscall sigreturn, or a provided
 * user-mode trampoline.
 */

static int setup_frame(struct ksignal *ksig, sigset_t *set,
                       struct pt_regs *regs)
{
        struct sigframe __user *frame;
        unsigned long return_ip;
        int err = 0;

        frame = get_sigframe(ksig, sizeof(*frame));

        if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
                return -EFAULT;

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

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

        /* Set up to return from userspace.  If provided, use a stub
           already in userspace.  */
        if (ksig->ka.sa.sa_flags & SA_RESTORER) {
                return_ip = (unsigned long)ksig->ka.sa.sa_restorer;
        } else {
                /* trampoline - the desired return ip is the retcode itself */
                return_ip = (unsigned long)&frame->retcode;
                /* This is movu.w __NR_sigreturn, r9; break 13; */
                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)
                return -EFAULT;

        /* Set up registers for signal handler */

        regs->irp = (unsigned long) ksig->ka.sa.sa_handler;  /* what we enter NOW   */
        regs->srp = return_ip;                          /* what we enter LATER */
        regs->r10 = ksig->sig;                                /* first argument is signo */

        /* actually move the usp to reflect the stacked frame */

        wrusp((unsigned long)frame);

        return 0;
}

static int setup_rt_frame(struct ksignal *ksig, sigset_t *set,
                          struct pt_regs *regs)
{
        struct rt_sigframe __user *frame;
        unsigned long return_ip;
        int err = 0;

        frame = get_sigframe(ksig, sizeof(*frame));

        if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
                return -EFAULT;

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

        /* 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));

        err |= __save_altstack(&frame->uc.uc_stack, rdusp());

        if (err)
                return -EFAULT;

        /* Set up to return from userspace.  If provided, use a stub
           already in userspace.  */
        if (ksig->ka.sa.sa_flags & SA_RESTORER) {
                return_ip = (unsigned long)ksig->ka.sa.sa_restorer;
        } else {
                /* trampoline - the desired return ip is the retcode itself */
                return_ip = (unsigned long)&frame->retcode;
                /* This is movu.w __NR_rt_sigreturn, r9; break 13; */
                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)
                return -EFAULT;

        /* Set up registers for signal handler */

        /* What we enter NOW   */
        regs->irp = (unsigned long) ksig->ka.sa.sa_handler;
        /* What we enter LATER */
        regs->srp = return_ip;
        /* First argument is signo */
        regs->r10 = ksig->sig;
        /* Second argument is (siginfo_t *) */
        regs->r11 = (unsigned long)&frame->info;
        /* Third argument is unused */
        regs->r12 = 0;

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

        return 0;
}

/*
 * OK, we're invoking a handler
 */

static inline void handle_signal(int canrestart, struct ksignal *ksig,
                                 struct pt_regs *regs)
{
        sigset_t *oldset = sigmask_to_save();
        int ret;

        /* Are we from a system call? */
        if (canrestart) {
                /* If so, check system call restarting.. */
                switch (regs->r10) {
                case -ERESTART_RESTARTBLOCK:
                case -ERESTARTNOHAND:
                        /* ERESTARTNOHAND means that the syscall should
                         * only be restarted if there was no handler for
                         * the signal, and since we only get here if there
                         * is a handler, we don't restart */
                        regs->r10 = -EINTR;
                        break;
                case -ERESTARTSYS:
                        /* ERESTARTSYS means to restart the syscall if
                         * there is no handler or the handler was
                         * registered with SA_RESTART */
                        if (!(ksig->ka.sa.sa_flags & SA_RESTART)) {
                                regs->r10 = -EINTR;
                                break;
                        }
                /* fallthrough */
                case -ERESTARTNOINTR:
                        /* ERESTARTNOINTR means that the syscall should
                         * be called again after the signal handler returns. */
                        RESTART_CRIS_SYS(regs);
                }
        }

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

        signal_setup_done(ret, ksig, 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)
{
        struct ksignal ksig;

        /*
         * We want the common case to go fast, which
         * is why we may in certain cases get here from
         * kernel mode. Just return without doing anything
         * if so.
         */
        if (!user_mode(regs))
                return;

        if (get_signal(&ksig)) {
                /* Whee!  Actually deliver the signal.  */
                handle_signal(canrestart, &ksig, regs);
                return;
        }

        /* Did we come 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->irp -= 2;
                }
        }

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