// SPDX-License-Identifier: GPL-2.0
/*
 * Based on arch/arm/mm/extable.c
 */

#include <linux/bitfield.h>
#include <linux/extable.h>
#include <linux/uaccess.h>

#include <asm/asm-extable.h>
#include <asm/esr.h>
#include <asm/ptrace.h>

static bool cpy_faulted_on_uaccess(const struct exception_table_entry *ex,
                                   unsigned long esr)
{
        bool uaccess_is_write = FIELD_GET(EX_DATA_UACCESS_WRITE, ex->data);
        bool fault_on_write = esr & ESR_ELx_WNR;

        return uaccess_is_write == fault_on_write;
}

bool insn_may_access_user(unsigned long addr, unsigned long esr)
{
        const struct exception_table_entry *ex = search_exception_tables(addr);

        if (!ex)
                return false;

        switch (ex->type) {
        case EX_TYPE_UACCESS_CPY:
                return cpy_faulted_on_uaccess(ex, esr);
        default:
                return true;
        }
}

static inline unsigned long
get_ex_fixup(const struct exception_table_entry *ex)
{
        return ((unsigned long)&ex->fixup + ex->fixup);
}

static bool ex_handler_uaccess_err_zero(const struct exception_table_entry *ex,
                                        struct pt_regs *regs)
{
        int reg_err = FIELD_GET(EX_DATA_REG_ERR, ex->data);
        int reg_zero = FIELD_GET(EX_DATA_REG_ZERO, ex->data);

        pt_regs_write_reg(regs, reg_err, -EFAULT);
        pt_regs_write_reg(regs, reg_zero, 0);

        regs->pc = get_ex_fixup(ex);
        return true;
}

static bool ex_handler_uaccess_cpy(const struct exception_table_entry *ex,
                                   struct pt_regs *regs, unsigned long esr)
{
        /* Do not fix up faults on kernel memory accesses */
        if (!cpy_faulted_on_uaccess(ex, esr))
                return false;

        regs->pc = get_ex_fixup(ex);
        return true;
}

static bool
ex_handler_load_unaligned_zeropad(const struct exception_table_entry *ex,
                                  struct pt_regs *regs)
{
        int reg_data = FIELD_GET(EX_DATA_REG_DATA, ex->data);
        int reg_addr = FIELD_GET(EX_DATA_REG_ADDR, ex->data);
        unsigned long data, addr, offset;

        addr = pt_regs_read_reg(regs, reg_addr);

        offset = addr & 0x7UL;
        addr &= ~0x7UL;

        data = *(unsigned long*)addr;

#ifndef __AARCH64EB__
        data >>= 8 * offset;
#else
        data <<= 8 * offset;
#endif

        pt_regs_write_reg(regs, reg_data, data);

        regs->pc = get_ex_fixup(ex);
        return true;
}

bool fixup_exception(struct pt_regs *regs, unsigned long esr)
{
        const struct exception_table_entry *ex;

        ex = search_exception_tables(instruction_pointer(regs));
        if (!ex)
                return false;

        switch (ex->type) {
        case EX_TYPE_BPF:
                return ex_handler_bpf(ex, regs);
        case EX_TYPE_UACCESS_ERR_ZERO:
        case EX_TYPE_KACCESS_ERR_ZERO:
                return ex_handler_uaccess_err_zero(ex, regs);
        case EX_TYPE_UACCESS_CPY:
                return ex_handler_uaccess_cpy(ex, regs, esr);
        case EX_TYPE_LOAD_UNALIGNED_ZEROPAD:
                return ex_handler_load_unaligned_zeropad(ex, regs);
        }

        BUG();
}