x86/speculation/mds: Fix documentation typo

[linux/fpc-iii.git] / arch / x86 / kernel / kprobes / opt.c

/*
 *  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/extable.h>
#include <linux/kdebug.h>
#include <linux/kallsyms.h>
#include <linux/ftrace.h>
#include <linux/frame.h>

#include <asm/text-patching.h>
#include <asm/cacheflush.h>
#include <asm/desc.h>
#include <asm/pgtable.h>
#include <linux/uaccess.h>
#include <asm/alternative.h>
#include <asm/insn.h>
#include <asm/debugreg.h>
#include <asm/set_memory.h>
#include <asm/sections.h>
#include <asm/nospec-branch.h>

#include "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.
         */
        if (probe_kernel_read(buf, (void *)addr,
                MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
                return 0UL;

        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 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;
}

asm (
                        "optprobe_template_func:\n"
                        ".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"
                        ".type optprobe_template_func, @function\n"
                        ".size optprobe_template_func, .-optprobe_template_func\n");

void optprobe_template_func(void);
STACK_FRAME_NON_STANDARD(optprobe_template_func);
NOKPROBE_SYMBOL(optprobe_template_func);
NOKPROBE_SYMBOL(optprobe_template_entry);
NOKPROBE_SYMBOL(optprobe_template_val);
NOKPROBE_SYMBOL(optprobe_template_call);
NOKPROBE_SYMBOL(optprobe_template_end);

#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
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);
}
NOKPROBE_SYMBOL(optimized_callback);

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

        while (len < RELATIVEJUMP_SIZE) {
                ret = __copy_instruction(dest + len, src + len, &insn);
                if (!ret || !can_boost(&insn, src + 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 __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);
}

static int insn_is_indirect_jump(struct insn *insn)
{
        int ret = __insn_is_indirect_jump(insn);

#ifdef CONFIG_RETPOLINE
        /*
         * Jump to x86_indirect_thunk_* is treated as an indirect jump.
         * Note that even with CONFIG_RETPOLINE=y, the kernel compiled with
         * older gcc may use indirect jump. So we add this check instead of
         * replace indirect-jump check.
         */
        if (!ret)
                ret = insn_jump_into_range(insn,
                                (unsigned long)__indirect_thunk_start,
                                (unsigned long)__indirect_thunk_end -
                                (unsigned long)__indirect_thunk_start);
#endif
        return ret;
}

/* Decode whole function to ensure any instructions don't jump into target */
static int 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 and registers setup.
         */
        if (((paddr >= (unsigned long)__entry_text_start) &&
             (paddr <  (unsigned long)__entry_text_end)) ||
            ((paddr >= (unsigned long)__irqentry_text_start) &&
             (paddr <  (unsigned long)__irqentry_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 */
                unsigned long recovered_insn;
                if (search_exception_tables(addr))
                        /*
                         * Since some fixup code will jumps into this function,
                         * we can't optimize kprobe in this function.
                         */
                        return 0;
                recovered_insn = recover_probed_instruction(buf, addr);
                if (!recovered_insn)
                        return 0;
                kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
                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 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 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
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 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 arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
                                  struct kprobe *__unused)
{
        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) {
                __arch_remove_optimized_kprobe(op, 0);
                return -ERANGE;
        }

        buf = (u8 *)op->optinsn.insn;
        set_memory_rw((unsigned long)buf & PAGE_MASK, 1);

        /* 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);

        set_memory_ro((unsigned long)buf & PAGE_MASK, 1);

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

/*
 * Replace breakpoints (int3) with relative jumps.
 * Caller must call with locking kprobe_mutex and text_mutex.
 */
void arch_optimize_kprobes(struct list_head *oplist)
{
        struct optimized_kprobe *op, *tmp;
        u8 insn_buf[RELATIVEJUMP_SIZE];

        list_for_each_entry_safe(op, tmp, oplist, list) {
                s32 rel = (s32)((long)op->optinsn.insn -
                        ((long)op->kp.addr + RELATIVEJUMP_SIZE));

                WARN_ON(kprobe_disabled(&op->kp));

                /* 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;

                text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
                             op->optinsn.insn);

                list_del_init(&op->list);
        }
}

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

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

/*
 * 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;

        list_for_each_entry_safe(op, tmp, oplist, list) {
                arch_unoptimize_kprobe(op);
                list_move(&op->list, done_list);
        }
}

int 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;
}
NOKPROBE_SYMBOL(setup_detour_execution);