kprobes-opt.c

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/*
 *  Kernel Probes Jump Optimization (Optprobes)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (C) IBM Corporation, 2002, 2004
 * Copyright (C) Hitachi Ltd., 2012
 */
#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/hardirq.h>
#include <linux/preempt.h>
#include <linux/module.h>
#include <linux/kdebug.h>
#include <linux/kallsyms.h>
#include <linux/ftrace.h>

#include <asm/cacheflush.h>
#include <asm/desc.h>
#include <asm/pgtable.h>
#include <asm/uaccess.h>
#include <asm/alternative.h>
#include <asm/insn.h>
#include <asm/debugreg.h>

#include "kprobes-common.h"

unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
{
    struct optimized_kprobe *op;
    struct kprobe *kp;
    long offs;
    int i;

    for (i = 0; i < RELATIVEJUMP_SIZE; i++) {
        kp = get_kprobe((void *)addr - i);
        /* This function only handles jump-optimized kprobe */
        if (kp && kprobe_optimized(kp)) {
            op = container_of(kp, struct optimized_kprobe, kp);
            /* If op->list is not empty, op is under optimizing */
            if (list_empty(&op->list))
                goto found;
        }
    }

    return addr;
found:
    /*
     * If the kprobe can be optimized, original bytes which can be
     * overwritten by jump destination address. In this case, original
     * bytes must be recovered from op->optinsn.copied_insn buffer.
     */
    memcpy(buf, (void *)addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
    if (addr == (unsigned long)kp->addr) {
        buf[0] = kp->opcode;
        memcpy(buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
    } else {
        offs = addr - (unsigned long)kp->addr - 1;
        memcpy(buf, op->optinsn.copied_insn + offs, RELATIVE_ADDR_SIZE - offs);
    }

    return (unsigned long)buf;
}

/* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */
static void __kprobes synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
{
#ifdef CONFIG_X86_64
    *addr++ = 0x48;
    *addr++ = 0xbf;
#else
    *addr++ = 0xb8;
#endif
    *(unsigned long *)addr = val;
}

static void __used __kprobes kprobes_optinsn_template_holder(void)
{
    asm volatile (
            ".global optprobe_template_entry\n"
            "optprobe_template_entry:\n"
#ifdef CONFIG_X86_64
            /* We don't bother saving the ss register */
            "   pushq %rsp\n"
            "   pushfq\n"
            SAVE_REGS_STRING
            "   movq %rsp, %rsi\n"
            ".global optprobe_template_val\n"
            "optprobe_template_val:\n"
            ASM_NOP5
            ASM_NOP5
            ".global optprobe_template_call\n"
            "optprobe_template_call:\n"
            ASM_NOP5
            /* Move flags to rsp */
            "   movq 144(%rsp), %rdx\n"
            "   movq %rdx, 152(%rsp)\n"
            RESTORE_REGS_STRING
            /* Skip flags entry */
            "   addq $8, %rsp\n"
            "   popfq\n"
#else /* CONFIG_X86_32 */
            "   pushf\n"
            SAVE_REGS_STRING
            "   movl %esp, %edx\n"
            ".global optprobe_template_val\n"
            "optprobe_template_val:\n"
            ASM_NOP5
            ".global optprobe_template_call\n"
            "optprobe_template_call:\n"
            ASM_NOP5
            RESTORE_REGS_STRING
            "   addl $4, %esp\n"    /* skip cs */
            "   popf\n"
#endif
            ".global optprobe_template_end\n"
            "optprobe_template_end:\n");
}

#define TMPL_MOVE_IDX \
    ((long)&optprobe_template_val - (long)&optprobe_template_entry)
#define TMPL_CALL_IDX \
    ((long)&optprobe_template_call - (long)&optprobe_template_entry)
#define TMPL_END_IDX \
    ((long)&optprobe_template_end - (long)&optprobe_template_entry)

#define INT3_SIZE sizeof(kprobe_opcode_t)

/* Optimized kprobe call back function: called from optinsn */
static void __kprobes optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
{
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
    unsigned long flags;

    /* This is possible if op is under delayed unoptimizing */
    if (kprobe_disabled(&op->kp))
        return;

    local_irq_save(flags);
    if (kprobe_running()) {
        kprobes_inc_nmissed_count(&op->kp);
    } else {
        /* Save skipped registers */
#ifdef CONFIG_X86_64
        regs->cs = __KERNEL_CS;
#else
        regs->cs = __KERNEL_CS | get_kernel_rpl();
        regs->gs = 0;
#endif
        regs->ip = (unsigned long)op->kp.addr + INT3_SIZE;
        regs->orig_ax = ~0UL;

        __this_cpu_write(current_kprobe, &op->kp);
        kcb->kprobe_status = KPROBE_HIT_ACTIVE;
        opt_pre_handler(&op->kp, regs);
        __this_cpu_write(current_kprobe, NULL);
    }
    local_irq_restore(flags);
}

static int __kprobes copy_optimized_instructions(u8 *dest, u8 *src)
{
    int len = 0, ret;

    while (len < RELATIVEJUMP_SIZE) {
        ret = __copy_instruction(dest + len, src + len);
        if (!ret || !can_boost(dest + len))
            return -EINVAL;
        len += ret;
    }
    /* Check whether the address range is reserved */
    if (ftrace_text_reserved(src, src + len - 1) ||
        alternatives_text_reserved(src, src + len - 1) ||
        jump_label_text_reserved(src, src + len - 1))
        return -EBUSY;

    return len;
}

/* Check whether insn is indirect jump */
static int __kprobes insn_is_indirect_jump(struct insn *insn)
{
    return ((insn->opcode.bytes[0] == 0xff &&
        (X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
        insn->opcode.bytes[0] == 0xea); /* Segment based jump */
}

/* Check whether insn jumps into specified address range */
static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
{
    unsigned long target = 0;

    switch (insn->opcode.bytes[0]) {
    case 0xe0:  /* loopne */
    case 0xe1:  /* loope */
    case 0xe2:  /* loop */
    case 0xe3:  /* jcxz */
    case 0xe9:  /* near relative jump */
    case 0xeb:  /* short relative jump */
        break;
    case 0x0f:
        if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
            break;
        return 0;
    default:
        if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
            break;
        return 0;
    }
    target = (unsigned long)insn->next_byte + insn->immediate.value;

    return (start <= target && target <= start + len);
}

/* Decode whole function to ensure any instructions don't jump into target */
static int __kprobes can_optimize(unsigned long paddr)
{
    unsigned long addr, size = 0, offset = 0;
    struct insn insn;
    kprobe_opcode_t buf[MAX_INSN_SIZE];

    /* Lookup symbol including addr */
    if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
        return 0;

    /*
     * Do not optimize in the entry code due to the unstable
     * stack handling.
     */
    if ((paddr >= (unsigned long)__entry_text_start) &&
        (paddr <  (unsigned long)__entry_text_end))
        return 0;

    /* Check there is enough space for a relative jump. */
    if (size - offset < RELATIVEJUMP_SIZE)
        return 0;

    /* Decode instructions */
    addr = paddr - offset;
    while (addr < paddr - offset + size) { /* Decode until function end */
        if (search_exception_tables(addr))
            /*
             * Since some fixup code will jumps into this function,
             * we can't optimize kprobe in this function.
             */
            return 0;
        kernel_insn_init(&insn, (void *)recover_probed_instruction(buf, addr));
        insn_get_length(&insn);
        /* Another subsystem puts a breakpoint */
        if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
            return 0;
        /* Recover address */
        insn.kaddr = (void *)addr;
        insn.next_byte = (void *)(addr + insn.length);
        /* Check any instructions don't jump into target */
        if (insn_is_indirect_jump(&insn) ||
            insn_jump_into_range(&insn, paddr + INT3_SIZE,
                     RELATIVE_ADDR_SIZE))
            return 0;
        addr += insn.length;
    }

    return 1;
}

/* Check optimized_kprobe can actually be optimized. */
int __kprobes arch_check_optimized_kprobe(struct optimized_kprobe *op)
{
    int i;
    struct kprobe *p;

    for (i = 1; i < op->optinsn.size; i++) {
        p = get_kprobe(op->kp.addr + i);
        if (p && !kprobe_disabled(p))
            return -EEXIST;
    }

    return 0;
}

/* Check the addr is within the optimized instructions. */
int __kprobes
arch_within_optimized_kprobe(struct optimized_kprobe *op, unsigned long addr)
{
    return ((unsigned long)op->kp.addr <= addr &&
        (unsigned long)op->kp.addr + op->optinsn.size > addr);
}

/* Free optimized instruction slot */
static __kprobes
void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
{
    if (op->optinsn.insn) {
        free_optinsn_slot(op->optinsn.insn, dirty);
        op->optinsn.insn = NULL;
        op->optinsn.size = 0;
    }
}

void __kprobes arch_remove_optimized_kprobe(struct optimized_kprobe *op)
{
    __arch_remove_optimized_kprobe(op, 1);
}

/*
 * Copy replacing target instructions
 * Target instructions MUST be relocatable (checked inside)
 * This is called when new aggr(opt)probe is allocated or reused.
 */
int __kprobes arch_prepare_optimized_kprobe(struct optimized_kprobe *op)
{
    u8 *buf;
    int ret;
    long rel;

    if (!can_optimize((unsigned long)op->kp.addr))
        return -EILSEQ;

    op->optinsn.insn = get_optinsn_slot();
    if (!op->optinsn.insn)
        return -ENOMEM;

    /*
     * Verify if the address gap is in 2GB range, because this uses
     * a relative jump.
     */
    rel = (long)op->optinsn.insn - (long)op->kp.addr + RELATIVEJUMP_SIZE;
    if (abs(rel) > 0x7fffffff)
        return -ERANGE;

    buf = (u8 *)op->optinsn.insn;

    /* Copy instructions into the out-of-line buffer */
    ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr);
    if (ret < 0) {
        __arch_remove_optimized_kprobe(op, 0);
        return ret;
    }
    op->optinsn.size = ret;

    /* Copy arch-dep-instance from template */
    memcpy(buf, &optprobe_template_entry, TMPL_END_IDX);

    /* Set probe information */
    synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);

    /* Set probe function call */
    synthesize_relcall(buf + TMPL_CALL_IDX, optimized_callback);

    /* Set returning jmp instruction at the tail of out-of-line buffer */
    synthesize_reljump(buf + TMPL_END_IDX + op->optinsn.size,
               (u8 *)op->kp.addr + op->optinsn.size);

    flush_icache_range((unsigned long) buf,
               (unsigned long) buf + TMPL_END_IDX +
               op->optinsn.size + RELATIVEJUMP_SIZE);
    return 0;
}

#define MAX_OPTIMIZE_PROBES 256
static struct text_poke_param *jump_poke_params;
static struct jump_poke_buffer {
    u8 buf[RELATIVEJUMP_SIZE];
} *jump_poke_bufs;

static void __kprobes setup_optimize_kprobe(struct text_poke_param *tprm,
                        u8 *insn_buf,
                        struct optimized_kprobe *op)
{
    s32 rel = (s32)((long)op->optinsn.insn -
            ((long)op->kp.addr + RELATIVEJUMP_SIZE));

    /* Backup instructions which will be replaced by jump address */
    memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_SIZE,
           RELATIVE_ADDR_SIZE);

    insn_buf[0] = RELATIVEJUMP_OPCODE;
    *(s32 *)(&insn_buf[1]) = rel;

    tprm->addr = op->kp.addr;
    tprm->opcode = insn_buf;
    tprm->len = RELATIVEJUMP_SIZE;
}

/*
 * Replace breakpoints (int3) with relative jumps.
 * Caller must call with locking kprobe_mutex and text_mutex.
 */
void __kprobes arch_optimize_kprobes(struct list_head *oplist)
{
    struct optimized_kprobe *op, *tmp;
    int c = 0;

    list_for_each_entry_safe(op, tmp, oplist, list) {
        WARN_ON(kprobe_disabled(&op->kp));
        /* Setup param */
        setup_optimize_kprobe(&jump_poke_params[c],
                      jump_poke_bufs[c].buf, op);
        list_del_init(&op->list);
        if (++c >= MAX_OPTIMIZE_PROBES)
            break;
    }

    /*
     * text_poke_smp doesn't support NMI/MCE code modifying.
     * However, since kprobes itself also doesn't support NMI/MCE
     * code probing, it's not a problem.
     */
    text_poke_smp_batch(jump_poke_params, c);
}

static void __kprobes setup_unoptimize_kprobe(struct text_poke_param *tprm,
                          u8 *insn_buf,
                          struct optimized_kprobe *op)
{
    /* Set int3 to first byte for kprobes */
    insn_buf[0] = BREAKPOINT_INSTRUCTION;
    memcpy(insn_buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);

    tprm->addr = op->kp.addr;
    tprm->opcode = insn_buf;
    tprm->len = RELATIVEJUMP_SIZE;
}

/*
 * Recover original instructions and breakpoints from relative jumps.
 * Caller must call with locking kprobe_mutex.
 */
extern void arch_unoptimize_kprobes(struct list_head *oplist,
                    struct list_head *done_list)
{
    struct optimized_kprobe *op, *tmp;
    int c = 0;

    list_for_each_entry_safe(op, tmp, oplist, list) {
        /* Setup param */
        setup_unoptimize_kprobe(&jump_poke_params[c],
                    jump_poke_bufs[c].buf, op);
        list_move(&op->list, done_list);
        if (++c >= MAX_OPTIMIZE_PROBES)
            break;
    }

    /*
     * text_poke_smp doesn't support NMI/MCE code modifying.
     * However, since kprobes itself also doesn't support NMI/MCE
     * code probing, it's not a problem.
     */
    text_poke_smp_batch(jump_poke_params, c);
}

/* Replace a relative jump with a breakpoint (int3).  */
void __kprobes arch_unoptimize_kprobe(struct optimized_kprobe *op)
{
    u8 buf[RELATIVEJUMP_SIZE];

    /* Set int3 to first byte for kprobes */
    buf[0] = BREAKPOINT_INSTRUCTION;
    memcpy(buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
    text_poke_smp(op->kp.addr, buf, RELATIVEJUMP_SIZE);
}

int  __kprobes
setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
{
    struct optimized_kprobe *op;

    if (p->flags & KPROBE_FLAG_OPTIMIZED) {
        /* This kprobe is really able to run optimized path. */
        op = container_of(p, struct optimized_kprobe, kp);
        /* Detour through copied instructions */
        regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
        if (!reenter)
            reset_current_kprobe();
        preempt_enable_no_resched();
        return 1;
    }
    return 0;
}

int __kprobes arch_init_optprobes(void)
{
    /* Allocate code buffer and parameter array */
    jump_poke_bufs = kmalloc(sizeof(struct jump_poke_buffer) *
                 MAX_OPTIMIZE_PROBES, GFP_KERNEL);
    if (!jump_poke_bufs)
        return -ENOMEM;

    jump_poke_params = kmalloc(sizeof(struct text_poke_param) *
                   MAX_OPTIMIZE_PROBES, GFP_KERNEL);
    if (!jump_poke_params) {
        kfree(jump_poke_bufs);
        jump_poke_bufs = NULL;
        return -ENOMEM;
    }

    return 0;
}