arch/arm/mm/alignment.c

root/arch/arm/mm/alignment.c
// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/arch/arm/mm/alignment.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 *  Modifications for ARM processor (c) 1995-2001 Russell King
 *  Thumb alignment fault fixups (c) 2004 MontaVista Software, Inc.
 *  - Adapted from gdb/sim/arm/thumbemu.c -- Thumb instruction emulation.
 *    Copyright (C) 1996, Cygnus Software Technologies Ltd.
 */
#include <linux/moduleparam.h>
#include <linux/compiler.h>
#include <linux/kernel.h>
#include <linux/sched/debug.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/init.h>
#include <linux/sched/signal.h>
#include <linux/uaccess.h>
#include <linux/unaligned.h>

#include <asm/cp15.h>
#include <asm/system_info.h>
#include <asm/system_misc.h>
#include <asm/opcodes.h>

#include "fault.h"
#include "mm.h"

/*
 * 32-bit misaligned trap handler (c) 1998 San Mehat (CCC) -July 1998
 * /proc/sys/debug/alignment, modified and integrated into
 * Linux 2.1 by Russell King
 *
 * Speed optimisations and better fault handling by Russell King.
 *
 * *** NOTE ***
 * This code is not portable to processors with late data abort handling.
 */
#define CODING_BITS(i)  (i & 0x0e000000)
#define COND_BITS(i)    (i & 0xf0000000)

#define LDST_I_BIT(i)   (i & (1 << 26))         /* Immediate constant   */
#define LDST_P_BIT(i)   (i & (1 << 24))         /* Preindex             */
#define LDST_U_BIT(i)   (i & (1 << 23))         /* Add offset           */
#define LDST_W_BIT(i)   (i & (1 << 21))         /* Writeback            */
#define LDST_L_BIT(i)   (i & (1 << 20))         /* Load                 */

#define LDST_P_EQ_U(i)  ((((i) ^ ((i) >> 1)) & (1 << 23)) == 0)

#define LDSTHD_I_BIT(i) (i & (1 << 22))         /* double/half-word immed */
#define LDM_S_BIT(i)    (i & (1 << 22))         /* write CPSR from SPSR */

#define RN_BITS(i)      ((i >> 16) & 15)        /* Rn                   */
#define RD_BITS(i)      ((i >> 12) & 15)        /* Rd                   */
#define RM_BITS(i)      (i & 15)                /* Rm                   */

#define REGMASK_BITS(i) (i & 0xffff)
#define OFFSET_BITS(i)  (i & 0x0fff)

#define IS_SHIFT(i)     (i & 0x0ff0)
#define SHIFT_BITS(i)   ((i >> 7) & 0x1f)
#define SHIFT_TYPE(i)   (i & 0x60)
#define SHIFT_LSL       0x00
#define SHIFT_LSR       0x20
#define SHIFT_ASR       0x40
#define SHIFT_RORRRX    0x60

#define BAD_INSTR       0xdeadc0de

/* Thumb-2 32 bit format per ARMv7 DDI0406A A6.3, either f800h,e800h,f800h */
#define IS_T32(hi16) \
        (((hi16) & 0xe000) == 0xe000 && ((hi16) & 0x1800))

static unsigned long ai_user;
static unsigned long ai_sys;
static void *ai_sys_last_pc;
static unsigned long ai_skipped;
static unsigned long ai_half;
static unsigned long ai_word;
static unsigned long ai_dword;
static unsigned long ai_multi;
static int ai_usermode;
static unsigned long cr_no_alignment;

core_param(alignment, ai_usermode, int, 0600);

#define UM_WARN         (1 << 0)
#define UM_FIXUP        (1 << 1)
#define UM_SIGNAL       (1 << 2)

/* Return true if and only if the ARMv6 unaligned access model is in use. */
static bool cpu_is_v6_unaligned(void)
{
        return cpu_architecture() >= CPU_ARCH_ARMv6 && get_cr() & CR_U;
}

static int safe_usermode(int new_usermode, bool warn)
{
        /*
         * ARMv6 and later CPUs can perform unaligned accesses for
         * most single load and store instructions up to word size.
         * LDM, STM, LDRD and STRD still need to be handled.
         *
         * Ignoring the alignment fault is not an option on these
         * CPUs since we spin re-faulting the instruction without
         * making any progress.
         */
        if (cpu_is_v6_unaligned() && !(new_usermode & (UM_FIXUP | UM_SIGNAL))) {
                new_usermode |= UM_FIXUP;

                if (warn)
                        pr_warn("alignment: ignoring faults is unsafe on this CPU.  Defaulting to fixup mode.\n");
        }

        return new_usermode;
}

#ifdef CONFIG_PROC_FS
static const char *usermode_action[] = {
        "ignored",
        "warn",
        "fixup",
        "fixup+warn",
        "signal",
        "signal+warn"
};

static int alignment_proc_show(struct seq_file *m, void *v)
{
        seq_printf(m, "User:\t\t%lu\n", ai_user);
        seq_printf(m, "System:\t\t%lu (%pS)\n", ai_sys, ai_sys_last_pc);
        seq_printf(m, "Skipped:\t%lu\n", ai_skipped);
        seq_printf(m, "Half:\t\t%lu\n", ai_half);
        seq_printf(m, "Word:\t\t%lu\n", ai_word);
        if (cpu_architecture() >= CPU_ARCH_ARMv5TE)
                seq_printf(m, "DWord:\t\t%lu\n", ai_dword);
        seq_printf(m, "Multi:\t\t%lu\n", ai_multi);
        seq_printf(m, "User faults:\t%i (%s)\n", ai_usermode,
                        usermode_action[ai_usermode]);

        return 0;
}

static int alignment_proc_open(struct inode *inode, struct file *file)
{
        return single_open(file, alignment_proc_show, NULL);
}

static ssize_t alignment_proc_write(struct file *file, const char __user *buffer,
                                    size_t count, loff_t *pos)
{
        char mode;

        if (count > 0) {
                if (get_user(mode, buffer))
                        return -EFAULT;
                if (mode >= '0' && mode <= '5')
                        ai_usermode = safe_usermode(mode - '0', true);
        }
        return count;
}

static const struct proc_ops alignment_proc_ops = {
        .proc_open      = alignment_proc_open,
        .proc_read      = seq_read,
        .proc_lseek     = seq_lseek,
        .proc_release   = single_release,
        .proc_write     = alignment_proc_write,
};
#endif /* CONFIG_PROC_FS */

union offset_union {
        unsigned long un;
          signed long sn;
};

#define TYPE_ERROR      0
#define TYPE_FAULT      1
#define TYPE_LDST       2
#define TYPE_DONE       3

#ifdef __ARMEB__
#define BE              1
#define FIRST_BYTE_16   "mov    %1, %1, ror #8\n"
#define FIRST_BYTE_32   "mov    %1, %1, ror #24\n"
#define NEXT_BYTE       "ror #24"
#else
#define BE              0
#define FIRST_BYTE_16
#define FIRST_BYTE_32
#define NEXT_BYTE       "lsr #8"
#endif

#define __get8_unaligned_check(ins,val,addr,err)        \
        __asm__(                                        \
 ARM(   "1:     "ins"   %1, [%2], #1\n" )               \
 THUMB( "1:     "ins"   %1, [%2]\n"     )               \
 THUMB( "       add     %2, %2, #1\n"   )               \
        "2:\n"                                          \
        "       .pushsection .text.fixup,\"ax\"\n"      \
        "       .align  2\n"                            \
        "3:     mov     %0, #1\n"                       \
        "       b       2b\n"                           \
        "       .popsection\n"                          \
        "       .pushsection __ex_table,\"a\"\n"        \
        "       .align  3\n"                            \
        "       .long   1b, 3b\n"                       \
        "       .popsection\n"                          \
        : "=r" (err), "=&r" (val), "=r" (addr)          \
        : "0" (err), "2" (addr))

#define __get16_unaligned_check(ins,val,addr)                   \
        do {                                                    \
                unsigned int err = 0, v, a = addr;              \
                __get8_unaligned_check(ins,v,a,err);            \
                val =  v << ((BE) ? 8 : 0);                     \
                __get8_unaligned_check(ins,v,a,err);            \
                val |= v << ((BE) ? 0 : 8);                     \
                if (err)                                        \
                        goto fault;                             \
        } while (0)

#define get16_unaligned_check(val,addr) \
        __get16_unaligned_check("ldrb",val,addr)

#define get16t_unaligned_check(val,addr) \
        __get16_unaligned_check("ldrbt",val,addr)

#define __get32_unaligned_check(ins,val,addr)                   \
        do {                                                    \
                unsigned int err = 0, v, a = addr;              \
                __get8_unaligned_check(ins,v,a,err);            \
                val =  v << ((BE) ? 24 :  0);                   \
                __get8_unaligned_check(ins,v,a,err);            \
                val |= v << ((BE) ? 16 :  8);                   \
                __get8_unaligned_check(ins,v,a,err);            \
                val |= v << ((BE) ?  8 : 16);                   \
                __get8_unaligned_check(ins,v,a,err);            \
                val |= v << ((BE) ?  0 : 24);                   \
                if (err)                                        \
                        goto fault;                             \
        } while (0)

#define get32_unaligned_check(val,addr) \
        __get32_unaligned_check("ldrb",val,addr)

#define get32t_unaligned_check(val,addr) \
        __get32_unaligned_check("ldrbt",val,addr)

#define __put16_unaligned_check(ins,val,addr)                   \
        do {                                                    \
                unsigned int err = 0, v = val, a = addr;        \
                __asm__( FIRST_BYTE_16                          \
         ARM(   "1:     "ins"   %1, [%2], #1\n" )               \
         THUMB( "1:     "ins"   %1, [%2]\n"     )               \
         THUMB( "       add     %2, %2, #1\n"   )               \
                "       mov     %1, %1, "NEXT_BYTE"\n"          \
                "2:     "ins"   %1, [%2]\n"                     \
                "3:\n"                                          \
                "       .pushsection .text.fixup,\"ax\"\n"      \
                "       .align  2\n"                            \
                "4:     mov     %0, #1\n"                       \
                "       b       3b\n"                           \
                "       .popsection\n"                          \
                "       .pushsection __ex_table,\"a\"\n"        \
                "       .align  3\n"                            \
                "       .long   1b, 4b\n"                       \
                "       .long   2b, 4b\n"                       \
                "       .popsection\n"                          \
                : "=r" (err), "=&r" (v), "=&r" (a)              \
                : "0" (err), "1" (v), "2" (a));                 \
                if (err)                                        \
                        goto fault;                             \
        } while (0)

#define put16_unaligned_check(val,addr)  \
        __put16_unaligned_check("strb",val,addr)

#define put16t_unaligned_check(val,addr) \
        __put16_unaligned_check("strbt",val,addr)

#define __put32_unaligned_check(ins,val,addr)                   \
        do {                                                    \
                unsigned int err = 0, v = val, a = addr;        \
                __asm__( FIRST_BYTE_32                          \
         ARM(   "1:     "ins"   %1, [%2], #1\n" )               \
         THUMB( "1:     "ins"   %1, [%2]\n"     )               \
         THUMB( "       add     %2, %2, #1\n"   )               \
                "       mov     %1, %1, "NEXT_BYTE"\n"          \
         ARM(   "2:     "ins"   %1, [%2], #1\n" )               \
         THUMB( "2:     "ins"   %1, [%2]\n"     )               \
         THUMB( "       add     %2, %2, #1\n"   )               \
                "       mov     %1, %1, "NEXT_BYTE"\n"          \
         ARM(   "3:     "ins"   %1, [%2], #1\n" )               \
         THUMB( "3:     "ins"   %1, [%2]\n"     )               \
         THUMB( "       add     %2, %2, #1\n"   )               \
                "       mov     %1, %1, "NEXT_BYTE"\n"          \
                "4:     "ins"   %1, [%2]\n"                     \
                "5:\n"                                          \
                "       .pushsection .text.fixup,\"ax\"\n"      \
                "       .align  2\n"                            \
                "6:     mov     %0, #1\n"                       \
                "       b       5b\n"                           \
                "       .popsection\n"                          \
                "       .pushsection __ex_table,\"a\"\n"        \
                "       .align  3\n"                            \
                "       .long   1b, 6b\n"                       \
                "       .long   2b, 6b\n"                       \
                "       .long   3b, 6b\n"                       \
                "       .long   4b, 6b\n"                       \
                "       .popsection\n"                          \
                : "=r" (err), "=&r" (v), "=&r" (a)              \
                : "0" (err), "1" (v), "2" (a));                 \
                if (err)                                        \
                        goto fault;                             \
        } while (0)

#define put32_unaligned_check(val,addr) \
        __put32_unaligned_check("strb", val, addr)

#define put32t_unaligned_check(val,addr) \
        __put32_unaligned_check("strbt", val, addr)

static void
do_alignment_finish_ldst(unsigned long addr, u32 instr, struct pt_regs *regs, union offset_union offset)
{
        if (!LDST_U_BIT(instr))
                offset.un = -offset.un;

        if (!LDST_P_BIT(instr))
                addr += offset.un;

        if (!LDST_P_BIT(instr) || LDST_W_BIT(instr))
                regs->uregs[RN_BITS(instr)] = addr;
}

static int
do_alignment_ldrhstrh(unsigned long addr, u32 instr, struct pt_regs *regs)
{
        unsigned int rd = RD_BITS(instr);

        ai_half += 1;

        if (user_mode(regs))
                goto user;

        if (LDST_L_BIT(instr)) {
                unsigned long val;
                get16_unaligned_check(val, addr);

                /* signed half-word? */
                if (instr & 0x40)
                        val = (signed long)((signed short) val);

                regs->uregs[rd] = val;
        } else
                put16_unaligned_check(regs->uregs[rd], addr);

        return TYPE_LDST;

 user:
        if (LDST_L_BIT(instr)) {
                unsigned long val;
                unsigned int __ua_flags = uaccess_save_and_enable();

                get16t_unaligned_check(val, addr);
                uaccess_restore(__ua_flags);

                /* signed half-word? */
                if (instr & 0x40)
                        val = (signed long)((signed short) val);

                regs->uregs[rd] = val;
        } else {
                unsigned int __ua_flags = uaccess_save_and_enable();
                put16t_unaligned_check(regs->uregs[rd], addr);
                uaccess_restore(__ua_flags);
        }

        return TYPE_LDST;

 fault:
        return TYPE_FAULT;
}

static int
do_alignment_ldrdstrd(unsigned long addr, u32 instr, struct pt_regs *regs)
{
        unsigned int rd = RD_BITS(instr);
        unsigned int rd2;
        int load;

        if ((instr & 0xfe000000) == 0xe8000000) {
                /* ARMv7 Thumb-2 32-bit LDRD/STRD */
                rd2 = (instr >> 8) & 0xf;
                load = !!(LDST_L_BIT(instr));
        } else if (((rd & 1) == 1) || (rd == 14))
                goto bad;
        else {
                load = ((instr & 0xf0) == 0xd0);
                rd2 = rd + 1;
        }

        ai_dword += 1;

        if (user_mode(regs))
                goto user;

        if (load) {
                unsigned long val;
                get32_unaligned_check(val, addr);
                regs->uregs[rd] = val;
                get32_unaligned_check(val, addr + 4);
                regs->uregs[rd2] = val;
        } else {
                put32_unaligned_check(regs->uregs[rd], addr);
                put32_unaligned_check(regs->uregs[rd2], addr + 4);
        }

        return TYPE_LDST;

 user:
        if (load) {
                unsigned long val, val2;
                unsigned int __ua_flags = uaccess_save_and_enable();

                get32t_unaligned_check(val, addr);
                get32t_unaligned_check(val2, addr + 4);

                uaccess_restore(__ua_flags);

                regs->uregs[rd] = val;
                regs->uregs[rd2] = val2;
        } else {
                unsigned int __ua_flags = uaccess_save_and_enable();
                put32t_unaligned_check(regs->uregs[rd], addr);
                put32t_unaligned_check(regs->uregs[rd2], addr + 4);
                uaccess_restore(__ua_flags);
        }

        return TYPE_LDST;
 bad:
        return TYPE_ERROR;
 fault:
        return TYPE_FAULT;
}

static int
do_alignment_ldrstr(unsigned long addr, u32 instr, struct pt_regs *regs)
{
        unsigned int rd = RD_BITS(instr);

        ai_word += 1;

        if ((!LDST_P_BIT(instr) && LDST_W_BIT(instr)) || user_mode(regs))
                goto trans;

        if (LDST_L_BIT(instr)) {
                unsigned int val;
                get32_unaligned_check(val, addr);
                regs->uregs[rd] = val;
        } else
                put32_unaligned_check(regs->uregs[rd], addr);
        return TYPE_LDST;

 trans:
        if (LDST_L_BIT(instr)) {
                unsigned int val;
                unsigned int __ua_flags = uaccess_save_and_enable();
                get32t_unaligned_check(val, addr);
                uaccess_restore(__ua_flags);
                regs->uregs[rd] = val;
        } else {
                unsigned int __ua_flags = uaccess_save_and_enable();
                put32t_unaligned_check(regs->uregs[rd], addr);
                uaccess_restore(__ua_flags);
        }
        return TYPE_LDST;

 fault:
        return TYPE_FAULT;
}

/*
 * LDM/STM alignment handler.
 *
 * There are 4 variants of this instruction:
 *
 * B = rn pointer before instruction, A = rn pointer after instruction
 *              ------ increasing address ----->
 *              |    | r0 | r1 | ... | rx |    |
 * PU = 01             B                    A
 * PU = 11        B                    A
 * PU = 00        A                    B
 * PU = 10             A                    B
 */
static int
do_alignment_ldmstm(unsigned long addr, u32 instr, struct pt_regs *regs)
{
        unsigned int rd, rn, correction, nr_regs, regbits;
        unsigned long eaddr, newaddr;

        if (LDM_S_BIT(instr))
                goto bad;

        correction = 4; /* processor implementation defined */
        regs->ARM_pc += correction;

        ai_multi += 1;

        /* count the number of registers in the mask to be transferred */
        nr_regs = hweight16(REGMASK_BITS(instr)) * 4;

        rn = RN_BITS(instr);
        newaddr = eaddr = regs->uregs[rn];

        if (!LDST_U_BIT(instr))
                nr_regs = -nr_regs;
        newaddr += nr_regs;
        if (!LDST_U_BIT(instr))
                eaddr = newaddr;

        if (LDST_P_EQ_U(instr)) /* U = P */
                eaddr += 4;

        /*
         * For alignment faults on the ARM922T/ARM920T the MMU  makes
         * the FSR (and hence addr) equal to the updated base address
         * of the multiple access rather than the restored value.
         * Switch this message off if we've got a ARM92[02], otherwise
         * [ls]dm alignment faults are noisy!
         */
#if !(defined CONFIG_CPU_ARM922T)  && !(defined CONFIG_CPU_ARM920T)
        /*
         * This is a "hint" - we already have eaddr worked out by the
         * processor for us.
         */
        if (addr != eaddr) {
                pr_err("LDMSTM: PC = %08lx, instr = %08x, "
                        "addr = %08lx, eaddr = %08lx\n",
                         instruction_pointer(regs), instr, addr, eaddr);
                show_regs(regs);
        }
#endif

        if (user_mode(regs)) {
                unsigned int __ua_flags = uaccess_save_and_enable();
                for (regbits = REGMASK_BITS(instr), rd = 0; regbits;
                     regbits >>= 1, rd += 1)
                        if (regbits & 1) {
                                if (LDST_L_BIT(instr)) {
                                        unsigned int val;
                                        get32t_unaligned_check(val, eaddr);
                                        regs->uregs[rd] = val;
                                } else
                                        put32t_unaligned_check(regs->uregs[rd], eaddr);
                                eaddr += 4;
                        }
                uaccess_restore(__ua_flags);
        } else {
                for (regbits = REGMASK_BITS(instr), rd = 0; regbits;
                     regbits >>= 1, rd += 1)
                        if (regbits & 1) {
                                if (LDST_L_BIT(instr)) {
                                        unsigned int val;
                                        get32_unaligned_check(val, eaddr);
                                        regs->uregs[rd] = val;
                                } else
                                        put32_unaligned_check(regs->uregs[rd], eaddr);
                                eaddr += 4;
                        }
        }

        if (LDST_W_BIT(instr))
                regs->uregs[rn] = newaddr;
        if (!LDST_L_BIT(instr) || !(REGMASK_BITS(instr) & (1 << 15)))
                regs->ARM_pc -= correction;
        return TYPE_DONE;

fault:
        regs->ARM_pc -= correction;
        return TYPE_FAULT;

bad:
        pr_err("Alignment trap: not handling ldm with s-bit set\n");
        return TYPE_ERROR;
}

/*
 * Convert Thumb ld/st instruction forms to equivalent ARM instructions so
 * we can reuse ARM userland alignment fault fixups for Thumb.
 *
 * This implementation was initially based on the algorithm found in
 * gdb/sim/arm/thumbemu.c. It is basically just a code reduction of same
 * to convert only Thumb ld/st instruction forms to equivalent ARM forms.
 *
 * NOTES:
 * 1. Comments below refer to ARM ARM DDI0100E Thumb Instruction sections.
 * 2. If for some reason we're passed an non-ld/st Thumb instruction to
 *    decode, we return 0xdeadc0de. This should never happen under normal
 *    circumstances but if it does, we've got other problems to deal with
 *    elsewhere and we obviously can't fix those problems here.
 */

static unsigned long
thumb2arm(u16 tinstr)
{
        u32 L = (tinstr & (1<<11)) >> 11;

        switch ((tinstr & 0xf800) >> 11) {
        /* 6.5.1 Format 1: */
        case 0x6000 >> 11:                              /* 7.1.52 STR(1) */
        case 0x6800 >> 11:                              /* 7.1.26 LDR(1) */
        case 0x7000 >> 11:                              /* 7.1.55 STRB(1) */
        case 0x7800 >> 11:                              /* 7.1.30 LDRB(1) */
                return 0xe5800000 |
                        ((tinstr & (1<<12)) << (22-12)) |       /* fixup */
                        (L<<20) |                               /* L==1? */
                        ((tinstr & (7<<0)) << (12-0)) |         /* Rd */
                        ((tinstr & (7<<3)) << (16-3)) |         /* Rn */
                        ((tinstr & (31<<6)) >>                  /* immed_5 */
                                (6 - ((tinstr & (1<<12)) ? 0 : 2)));
        case 0x8000 >> 11:                              /* 7.1.57 STRH(1) */
        case 0x8800 >> 11:                              /* 7.1.32 LDRH(1) */
                return 0xe1c000b0 |
                        (L<<20) |                               /* L==1? */
                        ((tinstr & (7<<0)) << (12-0)) |         /* Rd */
                        ((tinstr & (7<<3)) << (16-3)) |         /* Rn */
                        ((tinstr & (7<<6)) >> (6-1)) |   /* immed_5[2:0] */
                        ((tinstr & (3<<9)) >> (9-8));    /* immed_5[4:3] */

        /* 6.5.1 Format 2: */
        case 0x5000 >> 11:
        case 0x5800 >> 11:
                {
                        static const u32 subset[8] = {
                                0xe7800000,             /* 7.1.53 STR(2) */
                                0xe18000b0,             /* 7.1.58 STRH(2) */
                                0xe7c00000,             /* 7.1.56 STRB(2) */
                                0xe19000d0,             /* 7.1.34 LDRSB */
                                0xe7900000,             /* 7.1.27 LDR(2) */
                                0xe19000b0,             /* 7.1.33 LDRH(2) */
                                0xe7d00000,             /* 7.1.31 LDRB(2) */
                                0xe19000f0              /* 7.1.35 LDRSH */
                        };
                        return subset[(tinstr & (7<<9)) >> 9] |
                            ((tinstr & (7<<0)) << (12-0)) |     /* Rd */
                            ((tinstr & (7<<3)) << (16-3)) |     /* Rn */
                            ((tinstr & (7<<6)) >> (6-0));       /* Rm */
                }

        /* 6.5.1 Format 3: */
        case 0x4800 >> 11:                              /* 7.1.28 LDR(3) */
                /* NOTE: This case is not technically possible. We're
                 *       loading 32-bit memory data via PC relative
                 *       addressing mode. So we can and should eliminate
                 *       this case. But I'll leave it here for now.
                 */
                return 0xe59f0000 |
                    ((tinstr & (7<<8)) << (12-8)) |             /* Rd */
                    ((tinstr & 255) << (2-0));                  /* immed_8 */

        /* 6.5.1 Format 4: */
        case 0x9000 >> 11:                              /* 7.1.54 STR(3) */
        case 0x9800 >> 11:                              /* 7.1.29 LDR(4) */
                return 0xe58d0000 |
                        (L<<20) |                               /* L==1? */
                        ((tinstr & (7<<8)) << (12-8)) |         /* Rd */
                        ((tinstr & 255) << 2);                  /* immed_8 */

        /* 6.6.1 Format 1: */
        case 0xc000 >> 11:                              /* 7.1.51 STMIA */
        case 0xc800 >> 11:                              /* 7.1.25 LDMIA */
                {
                        u32 Rn = (tinstr & (7<<8)) >> 8;
                        u32 W = ((L<<Rn) & (tinstr&255)) ? 0 : 1<<21;

                        return 0xe8800000 | W | (L<<20) | (Rn<<16) |
                                (tinstr&255);
                }

        /* 6.6.1 Format 2: */
        case 0xb000 >> 11:                              /* 7.1.48 PUSH */
        case 0xb800 >> 11:                              /* 7.1.47 POP */
                if ((tinstr & (3 << 9)) == 0x0400) {
                        static const u32 subset[4] = {
                                0xe92d0000,     /* STMDB sp!,{registers} */
                                0xe92d4000,     /* STMDB sp!,{registers,lr} */
                                0xe8bd0000,     /* LDMIA sp!,{registers} */
                                0xe8bd8000      /* LDMIA sp!,{registers,pc} */
                        };
                        return subset[(L<<1) | ((tinstr & (1<<8)) >> 8)] |
                            (tinstr & 255);             /* register_list */
                }
                fallthrough;    /* for illegal instruction case */

        default:
                return BAD_INSTR;
        }
}

/*
 * Convert Thumb-2 32 bit LDM, STM, LDRD, STRD to equivalent instruction
 * handlable by ARM alignment handler, also find the corresponding handler,
 * so that we can reuse ARM userland alignment fault fixups for Thumb.
 *
 * @pinstr: original Thumb-2 instruction; returns new handlable instruction
 * @regs: register context.
 * @poffset: return offset from faulted addr for later writeback
 *
 * NOTES:
 * 1. Comments below refer to ARMv7 DDI0406A Thumb Instruction sections.
 * 2. Register name Rt from ARMv7 is same as Rd from ARMv6 (Rd is Rt)
 */
static void *
do_alignment_t32_to_handler(u32 *pinstr, struct pt_regs *regs,
                            union offset_union *poffset)
{
        u32 instr = *pinstr;
        u16 tinst1 = (instr >> 16) & 0xffff;
        u16 tinst2 = instr & 0xffff;

        switch (tinst1 & 0xffe0) {
        /* A6.3.5 Load/Store multiple */
        case 0xe880:            /* STM/STMIA/STMEA,LDM/LDMIA, PUSH/POP T2 */
        case 0xe8a0:            /* ...above writeback version */
        case 0xe900:            /* STMDB/STMFD, LDMDB/LDMEA */
        case 0xe920:            /* ...above writeback version */
                /* no need offset decision since handler calculates it */
                return do_alignment_ldmstm;

        case 0xf840:            /* POP/PUSH T3 (single register) */
                if (RN_BITS(instr) == 13 && (tinst2 & 0x09ff) == 0x0904) {
                        u32 L = !!(LDST_L_BIT(instr));
                        const u32 subset[2] = {
                                0xe92d0000,     /* STMDB sp!,{registers} */
                                0xe8bd0000,     /* LDMIA sp!,{registers} */
                        };
                        *pinstr = subset[L] | (1<<RD_BITS(instr));
                        return do_alignment_ldmstm;
                }
                /* Else fall through for illegal instruction case */
                break;

        /* A6.3.6 Load/store double, STRD/LDRD(immed, lit, reg) */
        case 0xe860:
        case 0xe960:
        case 0xe8e0:
        case 0xe9e0:
                poffset->un = (tinst2 & 0xff) << 2;
                fallthrough;

        case 0xe940:
        case 0xe9c0:
                return do_alignment_ldrdstrd;

        /*
         * No need to handle load/store instructions up to word size
         * since ARMv6 and later CPUs can perform unaligned accesses.
         */
        default:
                break;
        }
        return NULL;
}

static int alignment_get_arm(struct pt_regs *regs, u32 *ip, u32 *inst)
{
        u32 instr = 0;
        int fault;

        if (user_mode(regs))
                fault = get_user(instr, ip);
        else
                fault = get_kernel_nofault(instr, ip);

        *inst = __mem_to_opcode_arm(instr);

        return fault;
}

static int alignment_get_thumb(struct pt_regs *regs, u16 *ip, u16 *inst)
{
        u16 instr = 0;
        int fault;

        if (user_mode(regs))
                fault = get_user(instr, ip);
        else
                fault = get_kernel_nofault(instr, ip);

        *inst = __mem_to_opcode_thumb16(instr);

        return fault;
}

static int
do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        union offset_union offset;
        unsigned long instrptr;
        int (*handler)(unsigned long addr, u32 instr, struct pt_regs *regs);
        unsigned int type;
        u32 instr = 0;
        u16 tinstr = 0;
        int isize = 4;
        int thumb2_32b = 0;
        int fault;

        if (addr >= TASK_SIZE && user_mode(regs))
                harden_branch_predictor();

        if (interrupts_enabled(regs))
                local_irq_enable();

        instrptr = instruction_pointer(regs);

        if (thumb_mode(regs)) {
                u16 *ptr = (u16 *)(instrptr & ~1);

                fault = alignment_get_thumb(regs, ptr, &tinstr);
                if (!fault) {
                        if (cpu_architecture() >= CPU_ARCH_ARMv7 &&
                            IS_T32(tinstr)) {
                                /* Thumb-2 32-bit */
                                u16 tinst2;
                                fault = alignment_get_thumb(regs, ptr + 1, &tinst2);
                                instr = __opcode_thumb32_compose(tinstr, tinst2);
                                thumb2_32b = 1;
                        } else {
                                isize = 2;
                                instr = thumb2arm(tinstr);
                        }
                }
        } else {
                fault = alignment_get_arm(regs, (void *)instrptr, &instr);
        }

        if (fault) {
                type = TYPE_FAULT;
                goto bad_or_fault;
        }

        if (user_mode(regs))
                goto user;

        ai_sys += 1;
        ai_sys_last_pc = (void *)instruction_pointer(regs);

 fixup:

        regs->ARM_pc += isize;

        switch (CODING_BITS(instr)) {
        case 0x00000000:        /* 3.13.4 load/store instruction extensions */
                if (LDSTHD_I_BIT(instr))
                        offset.un = (instr & 0xf00) >> 4 | (instr & 15);
                else
                        offset.un = regs->uregs[RM_BITS(instr)];

                if ((instr & 0x000000f0) == 0x000000b0 || /* LDRH, STRH */
                    (instr & 0x001000f0) == 0x001000f0)   /* LDRSH */
                        handler = do_alignment_ldrhstrh;
                else if ((instr & 0x001000f0) == 0x000000d0 || /* LDRD */
                         (instr & 0x001000f0) == 0x000000f0)   /* STRD */
                        handler = do_alignment_ldrdstrd;
                else if ((instr & 0x01f00ff0) == 0x01000090) /* SWP */
                        goto swp;
                else
                        goto bad;
                break;

        case 0x04000000:        /* ldr or str immediate */
                if (COND_BITS(instr) == 0xf0000000) /* NEON VLDn, VSTn */
                        goto bad;
                offset.un = OFFSET_BITS(instr);
                handler = do_alignment_ldrstr;
                break;

        case 0x06000000:        /* ldr or str register */
                offset.un = regs->uregs[RM_BITS(instr)];

                if (IS_SHIFT(instr)) {
                        unsigned int shiftval = SHIFT_BITS(instr);

                        switch(SHIFT_TYPE(instr)) {
                        case SHIFT_LSL:
                                offset.un <<= shiftval;
                                break;

                        case SHIFT_LSR:
                                offset.un >>= shiftval;
                                break;

                        case SHIFT_ASR:
                                offset.sn >>= shiftval;
                                break;

                        case SHIFT_RORRRX:
                                if (shiftval == 0) {
                                        offset.un >>= 1;
                                        if (regs->ARM_cpsr & PSR_C_BIT)
                                                offset.un |= 1 << 31;
                                } else
                                        offset.un = offset.un >> shiftval |
                                                          offset.un << (32 - shiftval);
                                break;
                        }
                }
                handler = do_alignment_ldrstr;
                break;

        case 0x08000000:        /* ldm or stm, or thumb-2 32bit instruction */
                if (thumb2_32b) {
                        offset.un = 0;
                        handler = do_alignment_t32_to_handler(&instr, regs, &offset);
                } else {
                        offset.un = 0;
                        handler = do_alignment_ldmstm;
                }
                break;

        default:
                goto bad;
        }

        if (!handler)
                goto bad;
        type = handler(addr, instr, regs);

        if (type == TYPE_ERROR || type == TYPE_FAULT) {
                regs->ARM_pc -= isize;
                goto bad_or_fault;
        }

        if (type == TYPE_LDST)
                do_alignment_finish_ldst(addr, instr, regs, offset);

        if (thumb_mode(regs))
                regs->ARM_cpsr = it_advance(regs->ARM_cpsr);

        return 0;

 bad_or_fault:
        if (type == TYPE_ERROR)
                goto bad;
        /*
         * We got a fault - fix it up, or die.
         */
        do_bad_area(addr, fsr, regs);
        return 0;

 swp:
        pr_err("Alignment trap: not handling swp instruction\n");

 bad:
        /*
         * Oops, we didn't handle the instruction.
         */
        pr_err("Alignment trap: not handling instruction "
                "%0*x at [<%08lx>]\n",
                isize << 1,
                isize == 2 ? tinstr : instr, instrptr);
        ai_skipped += 1;
        return 1;

 user:
        ai_user += 1;

        if (ai_usermode & UM_WARN)
                printk("Alignment trap: %s (%d) PC=0x%08lx Instr=0x%0*x "
                       "Address=0x%08lx FSR 0x%03x\n", current->comm,
                        task_pid_nr(current), instrptr,
                        isize << 1,
                        isize == 2 ? tinstr : instr,
                        addr, fsr);

        if (ai_usermode & UM_FIXUP)
                goto fixup;

        if (ai_usermode & UM_SIGNAL) {
                force_sig_fault(SIGBUS, BUS_ADRALN, (void __user *)addr);
        } else {
                /*
                 * We're about to disable the alignment trap and return to
                 * user space.  But if an interrupt occurs before actually
                 * reaching user space, then the IRQ vector entry code will
                 * notice that we were still in kernel space and therefore
                 * the alignment trap won't be re-enabled in that case as it
                 * is presumed to be always on from kernel space.
                 * Let's prevent that race by disabling interrupts here (they
                 * are disabled on the way back to user space anyway in
                 * entry-common.S) and disable the alignment trap only if
                 * there is no work pending for this thread.
                 */
                raw_local_irq_disable();
                if (!(read_thread_flags() & _TIF_WORK_MASK))
                        set_cr(cr_no_alignment);
        }

        return 0;
}

static int __init noalign_setup(char *__unused)
{
        set_cr(__clear_cr(CR_A));
        return 1;
}
__setup("noalign", noalign_setup);

/*
 * This needs to be done after sysctl_init_bases(), otherwise sys/ will be
 * overwritten.  Actually, this shouldn't be in sys/ at all since
 * it isn't a sysctl, and it doesn't contain sysctl information.
 * We now locate it in /proc/cpu/alignment instead.
 */
static int __init alignment_init(void)
{
#ifdef CONFIG_PROC_FS
        struct proc_dir_entry *res;

        res = proc_create("cpu/alignment", S_IWUSR | S_IRUGO, NULL,
                          &alignment_proc_ops);
        if (!res)
                return -ENOMEM;
#endif

        if (cpu_is_v6_unaligned()) {
                set_cr(__clear_cr(CR_A));
                ai_usermode = safe_usermode(ai_usermode, false);
        }

        cr_no_alignment = get_cr() & ~CR_A;

        hook_fault_code(FAULT_CODE_ALIGNMENT, do_alignment, SIGBUS, BUS_ADRALN,
                        "alignment exception");

        /*
         * ARMv6K and ARMv7 use fault status 3 (0b00011) as Access Flag section
         * fault, not as alignment error.
         *
         * TODO: handle ARMv6K properly. Runtime check for 'K' extension is
         * needed.
         */
        if (cpu_architecture() <= CPU_ARCH_ARMv6) {
                hook_fault_code(3, do_alignment, SIGBUS, BUS_ADRALN,
                                "alignment exception");
        }

        return 0;
}

fs_initcall(alignment_init);