/*
 * Signal Handling for ARC
 *
 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * vineetg: Jan 2010 (Restarting of timer related syscalls)
 *
 * vineetg: Nov 2009 (Everything needed for TIF_RESTORE_SIGMASK)
 *  -do_signal() supports TIF_RESTORE_SIGMASK
 *  -do_signal() no loner needs oldset, required by OLD sys_sigsuspend
 *  -sys_rt_sigsuspend() now comes from generic code, so discard arch implemen
 *  -sys_sigsuspend() no longer needs to fudge ptregs, hence that arg removed
 *  -sys_sigsuspend() no longer loops for do_signal(), sets TIF_xxx and leaves
 *   the job to do_signal()
 *
 * vineetg: July 2009
 *  -Modified Code to support the uClibc provided userland sigreturn stub
 *   to avoid kernel synthesing it on user stack at runtime, costing TLB
 *   probes and Cache line flushes.
 *
 * vineetg: July 2009
 *  -In stash_usr_regs( ) and restore_usr_regs( ), save/restore of user regs
 *   in done in block copy rather than one word at a time.
 *   This saves around 2K of code and improves LMBench lat_sig <catch>
 *
 * rajeshwarr: Feb 2009
 *  - Support for Realtime Signals
 *
 * vineetg: Aug 11th 2008: Bug #94183
 *  -ViXS were still seeing crashes when using insmod to load drivers.
 *   It turned out that the code to change Execute permssions for TLB entries
 *   of user was not guarded for interrupts (mod_tlb_permission)
 *   This was causing TLB entries to be overwritten on unrelated indexes
 *
 * Vineetg: July 15th 2008: Bug #94183
 *  -Exception happens in Delay slot of a JMP, and before user space resumes,
 *   Signal is delivered (Ctrl + C) = >SIGINT.
 *   setup_frame( ) sets up PC,SP,BLINK to enable user space signal handler
 *   to run, but doesn't clear the Delay slot bit from status32. As a result,
 *   on resuming user mode, signal handler branches off to BTA of orig JMP
 *  -FIX: clear the DE bit from status32 in setup_frame( )
 *
 * Rahul Trivedi, Kanika Nema: Codito Technologies 2004
 */

#include <linux/signal.h>
#include <linux/ptrace.h>
#include <linux/personality.h>
#include <linux/uaccess.h>
#include <linux/syscalls.h>
#include <linux/tracehook.h>
#include <linux/sched/task_stack.h>

#include <asm/ucontext.h>

struct rt_sigframe {
        struct siginfo info;
        struct ucontext uc;
#define MAGIC_SIGALTSTK         0x07302004
        unsigned int sigret_magic;
};

static int
stash_usr_regs(struct rt_sigframe __user *sf, struct pt_regs *regs,
               sigset_t *set)
{
        int err;
        struct user_regs_struct uregs;

        uregs.scratch.bta       = regs->bta;
        uregs.scratch.lp_start  = regs->lp_start;
        uregs.scratch.lp_end    = regs->lp_end;
        uregs.scratch.lp_count  = regs->lp_count;
        uregs.scratch.status32  = regs->status32;
        uregs.scratch.ret       = regs->ret;
        uregs.scratch.blink     = regs->blink;
        uregs.scratch.fp        = regs->fp;
        uregs.scratch.gp        = regs->r26;
        uregs.scratch.r12       = regs->r12;
        uregs.scratch.r11       = regs->r11;
        uregs.scratch.r10       = regs->r10;
        uregs.scratch.r9        = regs->r9;
        uregs.scratch.r8        = regs->r8;
        uregs.scratch.r7        = regs->r7;
        uregs.scratch.r6        = regs->r6;
        uregs.scratch.r5        = regs->r5;
        uregs.scratch.r4        = regs->r4;
        uregs.scratch.r3        = regs->r3;
        uregs.scratch.r2        = regs->r2;
        uregs.scratch.r1        = regs->r1;
        uregs.scratch.r0        = regs->r0;
        uregs.scratch.sp        = regs->sp;

        err = __copy_to_user(&(sf->uc.uc_mcontext.regs.scratch), &uregs.scratch,
                             sizeof(sf->uc.uc_mcontext.regs.scratch));
        err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(sigset_t));

        return err;
}

static int restore_usr_regs(struct pt_regs *regs, struct rt_sigframe __user *sf)
{
        sigset_t set;
        int err;
        struct user_regs_struct uregs;

        err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
        err |= __copy_from_user(&uregs.scratch,
                                &(sf->uc.uc_mcontext.regs.scratch),
                                sizeof(sf->uc.uc_mcontext.regs.scratch));
        if (err)
                return err;

        set_current_blocked(&set);
        regs->bta       = uregs.scratch.bta;
        regs->lp_start  = uregs.scratch.lp_start;
        regs->lp_end    = uregs.scratch.lp_end;
        regs->lp_count  = uregs.scratch.lp_count;
        regs->status32  = uregs.scratch.status32;
        regs->ret       = uregs.scratch.ret;
        regs->blink     = uregs.scratch.blink;
        regs->fp        = uregs.scratch.fp;
        regs->r26       = uregs.scratch.gp;
        regs->r12       = uregs.scratch.r12;
        regs->r11       = uregs.scratch.r11;
        regs->r10       = uregs.scratch.r10;
        regs->r9        = uregs.scratch.r9;
        regs->r8        = uregs.scratch.r8;
        regs->r7        = uregs.scratch.r7;
        regs->r6        = uregs.scratch.r6;
        regs->r5        = uregs.scratch.r5;
        regs->r4        = uregs.scratch.r4;
        regs->r3        = uregs.scratch.r3;
        regs->r2        = uregs.scratch.r2;
        regs->r1        = uregs.scratch.r1;
        regs->r0        = uregs.scratch.r0;
        regs->sp        = uregs.scratch.sp;

        return 0;
}

static inline int is_do_ss_needed(unsigned int magic)
{
        if (MAGIC_SIGALTSTK == magic)
                return 1;
        else
                return 0;
}

SYSCALL_DEFINE0(rt_sigreturn)
{
        struct rt_sigframe __user *sf;
        unsigned int magic;
        struct pt_regs *regs = current_pt_regs();

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

        /* Since we stacked the signal on a word boundary,
         * then 'sp' should be word aligned here.  If it's
         * not, then the user is trying to mess with us.
         */
        if (regs->sp & 3)
                goto badframe;

        sf = (struct rt_sigframe __force __user *)(regs->sp);

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

        if (__get_user(magic, &sf->sigret_magic))
                goto badframe;

        if (unlikely(is_do_ss_needed(magic)))
                if (restore_altstack(&sf->uc.uc_stack))
                        goto badframe;

        if (restore_usr_regs(regs, sf))
                goto badframe;

        /* Don't restart from sigreturn */
        syscall_wont_restart(regs);

        /*
         * Ensure that sigreturn always returns to user mode (in case the
         * regs saved on user stack got fudged between save and sigreturn)
         * Otherwise it is easy to panic the kernel with a custom
         * signal handler and/or restorer which clobberes the status32/ret
         * to return to a bogus location in kernel mode.
         */
        regs->status32 |= STATUS_U_MASK;

        return regs->r0;

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

/*
 * Determine which stack to use..
 */
static inline void __user *get_sigframe(struct ksignal *ksig,
                                        struct pt_regs *regs,
                                        unsigned long framesize)
{
        unsigned long sp = sigsp(regs->sp, ksig);
        void __user *frame;

        /* No matter what happens, 'sp' must be word
         * aligned otherwise nasty things could happen
         */

        /* ATPCS B01 mandates 8-byte alignment */
        frame = (void __user *)((sp - framesize) & ~7);

        /* Check that we can actually write to the signal frame */
        if (!access_ok(VERIFY_WRITE, frame, framesize))
                frame = NULL;

        return frame;
}

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

        sf = get_sigframe(ksig, regs, sizeof(struct rt_sigframe));
        if (!sf)
                return 1;

        /*
         * w/o SA_SIGINFO, struct ucontext is partially populated (only
         * uc_mcontext/uc_sigmask) for kernel's normal user state preservation
         * during signal handler execution. This works for SA_SIGINFO as well
         * although the semantics are now overloaded (the same reg state can be
         * inspected by userland: but are they allowed to fiddle with it ?
         */
        err |= stash_usr_regs(sf, regs, set);

        /*
         * SA_SIGINFO requires 3 args to signal handler:
         *  #1: sig-no (common to any handler)
         *  #2: struct siginfo
         *  #3: struct ucontext (completely populated)
         */
        if (unlikely(ksig->ka.sa.sa_flags & SA_SIGINFO)) {
                err |= copy_siginfo_to_user(&sf->info, &ksig->info);
                err |= __put_user(0, &sf->uc.uc_flags);
                err |= __put_user(NULL, &sf->uc.uc_link);
                err |= __save_altstack(&sf->uc.uc_stack, regs->sp);

                /* setup args 2 and 3 for user mode handler */
                regs->r1 = (unsigned long)&sf->info;
                regs->r2 = (unsigned long)&sf->uc;

                /*
                 * small optim to avoid unconditonally calling do_sigaltstack
                 * in sigreturn path, now that we only have rt_sigreturn
                 */
                magic = MAGIC_SIGALTSTK;
        }

        err |= __put_user(magic, &sf->sigret_magic);
        if (err)
                return err;

        /* #1 arg to the user Signal handler */
        regs->r0 = ksig->sig;

        /* setup PC of user space signal handler */
        regs->ret = (unsigned long)ksig->ka.sa.sa_handler;

        /*
         * handler returns using sigreturn stub provided already by userpsace
         * If not, nuke the process right away
         */
        if(!(ksig->ka.sa.sa_flags & SA_RESTORER))
                return 1;

        regs->blink = (unsigned long)ksig->ka.sa.sa_restorer;

        /* User Stack for signal handler will be above the frame just carved */
        regs->sp = (unsigned long)sf;

        /*
         * Bug 94183, Clear the DE bit, so that when signal handler
         * starts to run, it doesn't use BTA
         */
        regs->status32 &= ~STATUS_DE_MASK;
        regs->status32 |= STATUS_L_MASK;

        return err;
}

static void arc_restart_syscall(struct k_sigaction *ka, struct pt_regs *regs)
{
        switch (regs->r0) {
        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->r0 = -EINTR;   /* ERESTART_xxx is internal */
                break;

        case -ERESTARTSYS:
                /*
                 * ERESTARTSYS means to restart the syscall if
                 * there is no handler or the handler was
                 * registered with SA_RESTART
                 */
                if (!(ka->sa.sa_flags & SA_RESTART)) {
                        regs->r0 = -EINTR;
                        break;
                }
                /* fallthrough */

        case -ERESTARTNOINTR:
                /*
                 * ERESTARTNOINTR means that the syscall should
                 * be called again after the signal handler returns.
                 * Setup reg state just as it was before doing the trap
                 * r0 has been clobbered with sys call ret code thus it
                 * needs to be reloaded with orig first arg to syscall
                 * in orig_r0. Rest of relevant reg-file:
                 * r8 (syscall num) and (r1 - r7) will be reset to
                 * their orig user space value when we ret from kernel
                 */
                regs->r0 = regs->orig_r0;
                regs->ret -= is_isa_arcv2() ? 2 : 4;
                break;
        }
}

/*
 * OK, we're invoking a handler
 */
static void
handle_signal(struct ksignal *ksig, struct pt_regs *regs)
{
        sigset_t *oldset = sigmask_to_save();
        int failed;

        /* Set up the stack frame */
        failed = setup_rt_frame(ksig, oldset, regs);

        signal_setup_done(failed, ksig, 0);
}

void do_signal(struct pt_regs *regs)
{
        struct ksignal ksig;
        int restart_scall;

        restart_scall = in_syscall(regs) && syscall_restartable(regs);

        if (get_signal(&ksig)) {
                if (restart_scall) {
                        arc_restart_syscall(&ksig.ka, regs);
                        syscall_wont_restart(regs);     /* No more restarts */
                }
                handle_signal(&ksig, regs);
                return;
        }

        if (restart_scall) {
                /* No handler for syscall: restart it */
                if (regs->r0 == -ERESTARTNOHAND ||
                    regs->r0 == -ERESTARTSYS || regs->r0 == -ERESTARTNOINTR) {
                        regs->r0 = regs->orig_r0;
                        regs->ret -= is_isa_arcv2() ? 2 : 4;
                } else if (regs->r0 == -ERESTART_RESTARTBLOCK) {
                        regs->r8 = __NR_restart_syscall;
                        regs->ret -= is_isa_arcv2() ? 2 : 4;
                }
                syscall_wont_restart(regs);     /* No more restarts */
        }

        /* If there's no signal to deliver, restore the saved sigmask back */
        restore_saved_sigmask();
}

void do_notify_resume(struct pt_regs *regs)
{
        /*
         * ASM glue gaurantees that this is only called when returning to
         * user mode
         */
        if (test_and_clear_thread_flag(TIF_NOTIFY_RESUME))
                tracehook_notify_resume(regs);
}