uprobes.c

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/*
 * User-space Probes (UProbes) for powerpc
 *
 * 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 IBM Corporation, 2007-2012
 *
 * Adapted from the x86 port by Ananth N Mavinakayanahalli <[email protected]>
 */
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/ptrace.h>
#include <linux/uprobes.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>

#include <asm/sstep.h>

#define UPROBE_TRAP_NR  UINT_MAX

int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
        struct mm_struct *mm, unsigned long addr)
{
    if (addr & 0x03)
        return -EINVAL;

    /*
     * We currently don't support a uprobe on an already
     * existing breakpoint instruction underneath
     */
    if (is_trap(auprobe->ainsn))
        return -ENOTSUPP;
    return 0;
}

/*
 * arch_uprobe_pre_xol - prepare to execute out of line.
 * @auprobe: the probepoint information.
 * @regs: reflects the saved user state of current task.
 */
int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
    struct arch_uprobe_task *autask = &current->utask->autask;

    autask->saved_trap_nr = current->thread.trap_nr;
    current->thread.trap_nr = UPROBE_TRAP_NR;
    regs->nip = current->utask->xol_vaddr;
    return 0;
}

unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
{
    return instruction_pointer(regs);
}

/*
 * If xol insn itself traps and generates a signal (SIGILL/SIGSEGV/etc),
 * then detect the case where a singlestepped instruction jumps back to its
 * own address. It is assumed that anything like do_page_fault/do_trap/etc
 * sets thread.trap_nr != UINT_MAX.
 *
 * arch_uprobe_pre_xol/arch_uprobe_post_xol save/restore thread.trap_nr,
 * arch_uprobe_xol_was_trapped() simply checks that ->trap_nr is not equal to
 * UPROBE_TRAP_NR == UINT_MAX set by arch_uprobe_pre_xol().
 */
bool arch_uprobe_xol_was_trapped(struct task_struct *t)
{
    if (t->thread.trap_nr != UPROBE_TRAP_NR)
        return true;

    return false;
}

/*
 * Called after single-stepping. To avoid the SMP problems that can
 * occur when we temporarily put back the original opcode to
 * single-step, we single-stepped a copy of the instruction.
 *
 * This function prepares to resume execution after the single-step.
 */
int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
    struct uprobe_task *utask = current->utask;

    WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);

    current->thread.trap_nr = utask->autask.saved_trap_nr;

    /*
     * On powerpc, except for loads and stores, most instructions
     * including ones that alter code flow (branches, calls, returns)
     * are emulated in the kernel. We get here only if the emulation
     * support doesn't exist and have to fix-up the next instruction
     * to be executed.
     */
    regs->nip = utask->vaddr + MAX_UINSN_BYTES;
    return 0;
}

/* callback routine for handling exceptions. */
int arch_uprobe_exception_notify(struct notifier_block *self,
                unsigned long val, void *data)
{
    struct die_args *args = data;
    struct pt_regs *regs = args->regs;

    /* regs == NULL is a kernel bug */
    if (WARN_ON(!regs))
        return NOTIFY_DONE;

    /* We are only interested in userspace traps */
    if (!user_mode(regs))
        return NOTIFY_DONE;

    switch (val) {
    case DIE_BPT:
        if (uprobe_pre_sstep_notifier(regs))
            return NOTIFY_STOP;
        break;
    case DIE_SSTEP:
        if (uprobe_post_sstep_notifier(regs))
            return NOTIFY_STOP;
    default:
        break;
    }
    return NOTIFY_DONE;
}

/*
 * This function gets called when XOL instruction either gets trapped or
 * the thread has a fatal signal, so reset the instruction pointer to its
 * probed address.
 */
void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
    struct uprobe_task *utask = current->utask;

    current->thread.trap_nr = utask->autask.saved_trap_nr;
    instruction_pointer_set(regs, utask->vaddr);
}

/*
 * See if the instruction can be emulated.
 * Returns true if instruction was emulated, false otherwise.
 */
bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
    int ret;

    /*
     * emulate_step() returns 1 if the insn was successfully emulated.
     * For all other cases, we need to single-step in hardware.
     */
    ret = emulate_step(regs, auprobe->ainsn);
    if (ret > 0)
        return true;

    return false;
}