// SPDX-License-Identifier: GPL-2.0
/*
 * unaligned.c: Unaligned load/store trap handling with special
 *              cases for the kernel to do them more quickly.
 *
 * Copyright (C) 1996 David S. Miller (davem@caip.rutgers.edu)
 * Copyright (C) 1996 Jakub Jelinek (jj@sunsite.mff.cuni.cz)
 */


#include <linux/kernel.h>
#include <linux/sched/signal.h>
#include <linux/mm.h>
#include <asm/ptrace.h>
#include <asm/processor.h>
#include <linux/uaccess.h>
#include <linux/smp.h>
#include <linux/perf_event.h>
#include <linux/extable.h>

#include <asm/setup.h>

#include "kernel.h"

enum direction {
        load,    /* ld, ldd, ldh, ldsh */
        store,   /* st, std, sth, stsh */
        both,    /* Swap, ldstub, etc. */
        fpload,
        fpstore,
        invalid,
};

static inline enum direction decode_direction(unsigned int insn)
{
        unsigned long tmp = (insn >> 21) & 1;

        if(!tmp)
                return load;
        else {
                if(((insn>>19)&0x3f) == 15)
                        return both;
                else
                        return store;
        }
}

/* 8 = double-word, 4 = word, 2 = half-word */
static inline int decode_access_size(unsigned int insn)
{
        insn = (insn >> 19) & 3;

        if(!insn)
                return 4;
        else if(insn == 3)
                return 8;
        else if(insn == 2)
                return 2;
        else {
                printk("Impossible unaligned trap. insn=%08x\n", insn);
                die_if_kernel("Byte sized unaligned access?!?!", current->thread.kregs);
                return 4; /* just to keep gcc happy. */
        }
}

/* 0x400000 = signed, 0 = unsigned */
static inline int decode_signedness(unsigned int insn)
{
        return (insn & 0x400000);
}

static inline void maybe_flush_windows(unsigned int rs1, unsigned int rs2,
                                       unsigned int rd)
{
        if(rs2 >= 16 || rs1 >= 16 || rd >= 16) {
                /* Wheee... */
                __asm__ __volatile__("save %sp, -0x40, %sp\n\t"
                                     "save %sp, -0x40, %sp\n\t"
                                     "save %sp, -0x40, %sp\n\t"
                                     "save %sp, -0x40, %sp\n\t"
                                     "save %sp, -0x40, %sp\n\t"
                                     "save %sp, -0x40, %sp\n\t"
                                     "save %sp, -0x40, %sp\n\t"
                                     "restore; restore; restore; restore;\n\t"
                                     "restore; restore; restore;\n\t");
        }
}

static inline int sign_extend_imm13(int imm)
{
        return imm << 19 >> 19;
}

static inline unsigned long fetch_reg(unsigned int reg, struct pt_regs *regs)
{
        struct reg_window32 *win;

        if(reg < 16)
                return (!reg ? 0 : regs->u_regs[reg]);

        /* Ho hum, the slightly complicated case. */
        win = (struct reg_window32 *) regs->u_regs[UREG_FP];
        return win->locals[reg - 16]; /* yes, I know what this does... */
}

static inline unsigned long safe_fetch_reg(unsigned int reg, struct pt_regs *regs)
{
        struct reg_window32 __user *win;
        unsigned long ret;

        if (reg < 16)
                return (!reg ? 0 : regs->u_regs[reg]);

        /* Ho hum, the slightly complicated case. */
        win = (struct reg_window32 __user *) regs->u_regs[UREG_FP];

        if ((unsigned long)win & 3)
                return -1;

        if (get_user(ret, &win->locals[reg - 16]))
                return -1;

        return ret;
}

static inline unsigned long *fetch_reg_addr(unsigned int reg, struct pt_regs *regs)
{
        struct reg_window32 *win;

        if(reg < 16)
                return &regs->u_regs[reg];
        win = (struct reg_window32 *) regs->u_regs[UREG_FP];
        return &win->locals[reg - 16];
}

static unsigned long compute_effective_address(struct pt_regs *regs,
                                               unsigned int insn)
{
        unsigned int rs1 = (insn >> 14) & 0x1f;
        unsigned int rs2 = insn & 0x1f;
        unsigned int rd = (insn >> 25) & 0x1f;

        if(insn & 0x2000) {
                maybe_flush_windows(rs1, 0, rd);
                return (fetch_reg(rs1, regs) + sign_extend_imm13(insn));
        } else {
                maybe_flush_windows(rs1, rs2, rd);
                return (fetch_reg(rs1, regs) + fetch_reg(rs2, regs));
        }
}

unsigned long safe_compute_effective_address(struct pt_regs *regs,
                                             unsigned int insn)
{
        unsigned int rs1 = (insn >> 14) & 0x1f;
        unsigned int rs2 = insn & 0x1f;
        unsigned int rd = (insn >> 25) & 0x1f;

        if(insn & 0x2000) {
                maybe_flush_windows(rs1, 0, rd);
                return (safe_fetch_reg(rs1, regs) + sign_extend_imm13(insn));
        } else {
                maybe_flush_windows(rs1, rs2, rd);
                return (safe_fetch_reg(rs1, regs) + safe_fetch_reg(rs2, regs));
        }
}

/* This is just to make gcc think panic does return... */
static void unaligned_panic(char *str)
{
        panic("%s", str);
}

/* una_asm.S */
extern int do_int_load(unsigned long *dest_reg, int size,
                       unsigned long *saddr, int is_signed);
extern int __do_int_store(unsigned long *dst_addr, int size,
                          unsigned long *src_val);

static int do_int_store(int reg_num, int size, unsigned long *dst_addr,
                        struct pt_regs *regs)
{
        unsigned long zero[2] = { 0, 0 };
        unsigned long *src_val;

        if (reg_num)
                src_val = fetch_reg_addr(reg_num, regs);
        else {
                src_val = &zero[0];
                if (size == 8)
                        zero[1] = fetch_reg(1, regs);
        }
        return __do_int_store(dst_addr, size, src_val);
}

extern void smp_capture(void);
extern void smp_release(void);

static inline void advance(struct pt_regs *regs)
{
        regs->pc   = regs->npc;
        regs->npc += 4;
}

static inline int floating_point_load_or_store_p(unsigned int insn)
{
        return (insn >> 24) & 1;
}

static inline int ok_for_kernel(unsigned int insn)
{
        return !floating_point_load_or_store_p(insn);
}

static void kernel_mna_trap_fault(struct pt_regs *regs, unsigned int insn)
{
        const struct exception_table_entry *entry;

        entry = search_exception_tables(regs->pc);
        if (!entry) {
                unsigned long address = compute_effective_address(regs, insn);
                if(address < PAGE_SIZE) {
                        printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference in mna handler");
                } else
                        printk(KERN_ALERT "Unable to handle kernel paging request in mna handler");
                printk(KERN_ALERT " at virtual address %08lx\n",address);
                printk(KERN_ALERT "current->{mm,active_mm}->context = %08lx\n",
                        (current->mm ? current->mm->context :
                        current->active_mm->context));
                printk(KERN_ALERT "current->{mm,active_mm}->pgd = %08lx\n",
                        (current->mm ? (unsigned long) current->mm->pgd :
                        (unsigned long) current->active_mm->pgd));
                die_if_kernel("Oops", regs);
                /* Not reached */
        }
        regs->pc = entry->fixup;
        regs->npc = regs->pc + 4;
}

asmlinkage void kernel_unaligned_trap(struct pt_regs *regs, unsigned int insn)
{
        enum direction dir = decode_direction(insn);
        int size = decode_access_size(insn);

        if(!ok_for_kernel(insn) || dir == both) {
                printk("Unsupported unaligned load/store trap for kernel at <%08lx>.\n",
                       regs->pc);
                unaligned_panic("Wheee. Kernel does fpu/atomic unaligned load/store.");
        } else {
                unsigned long addr = compute_effective_address(regs, insn);
                int err;

                perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, addr);
                switch (dir) {
                case load:
                        err = do_int_load(fetch_reg_addr(((insn>>25)&0x1f),
                                                         regs),
                                          size, (unsigned long *) addr,
                                          decode_signedness(insn));
                        break;

                case store:
                        err = do_int_store(((insn>>25)&0x1f), size,
                                           (unsigned long *) addr, regs);
                        break;
                default:
                        panic("Impossible kernel unaligned trap.");
                        /* Not reached... */
                }
                if (err)
                        kernel_mna_trap_fault(regs, insn);
                else
                        advance(regs);
        }
}

asmlinkage void user_unaligned_trap(struct pt_regs *regs, unsigned int insn)
{
        send_sig_fault(SIGBUS, BUS_ADRALN,
                       (void __user *)safe_compute_effective_address(regs, insn),
                       current);
}