ptrace.c

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/*
 * Copyright (C) 2004-2006 Atmel Corporation
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#undef DEBUG
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/ptrace.h>
#include <linux/errno.h>
#include <linux/user.h>
#include <linux/security.h>
#include <linux/unistd.h>
#include <linux/notifier.h>

#include <asm/traps.h>
#include <asm/uaccess.h>
#include <asm/ocd.h>
#include <asm/mmu_context.h>
#include <linux/kdebug.h>

static struct pt_regs *get_user_regs(struct task_struct *tsk)
{
    return (struct pt_regs *)((unsigned long)task_stack_page(tsk) +
                  THREAD_SIZE - sizeof(struct pt_regs));
}

void user_enable_single_step(struct task_struct *tsk)
{
    pr_debug("user_enable_single_step: pid=%u, PC=0x%08lx, SR=0x%08lx\n",
         tsk->pid, task_pt_regs(tsk)->pc, task_pt_regs(tsk)->sr);

    /*
     * We can't schedule in Debug mode, so when TIF_BREAKPOINT is
     * set, the system call or exception handler will do a
     * breakpoint to enter monitor mode before returning to
     * userspace.
     *
     * The monitor code will then notice that TIF_SINGLE_STEP is
     * set and return to userspace with single stepping enabled.
     * The CPU will then enter monitor mode again after exactly
     * one instruction has been executed, and the monitor code
     * will then send a SIGTRAP to the process.
     */
    set_tsk_thread_flag(tsk, TIF_BREAKPOINT);
    set_tsk_thread_flag(tsk, TIF_SINGLE_STEP);
}

void user_disable_single_step(struct task_struct *child)
{
    /* XXX(hch): a no-op here seems wrong.. */
}

/*
 * Called by kernel/ptrace.c when detaching
 *
 * Make sure any single step bits, etc. are not set
 */
void ptrace_disable(struct task_struct *child)
{
    clear_tsk_thread_flag(child, TIF_SINGLE_STEP);
    clear_tsk_thread_flag(child, TIF_BREAKPOINT);
    ocd_disable(child);
}

/*
 * Read the word at offset "offset" into the task's "struct user". We
 * actually access the pt_regs struct stored on the kernel stack.
 */
static int ptrace_read_user(struct task_struct *tsk, unsigned long offset,
                unsigned long __user *data)
{
    unsigned long *regs;
    unsigned long value;

    if (offset & 3 || offset >= sizeof(struct user)) {
        printk("ptrace_read_user: invalid offset 0x%08lx\n", offset);
        return -EIO;
    }

    regs = (unsigned long *)get_user_regs(tsk);

    value = 0;
    if (offset < sizeof(struct pt_regs))
        value = regs[offset / sizeof(regs[0])];

    pr_debug("ptrace_read_user(%s[%u], %#lx, %p) -> %#lx\n",
         tsk->comm, tsk->pid, offset, data, value);

    return put_user(value, data);
}

/*
 * Write the word "value" to offset "offset" into the task's "struct
 * user". We actually access the pt_regs struct stored on the kernel
 * stack.
 */
static int ptrace_write_user(struct task_struct *tsk, unsigned long offset,
                 unsigned long value)
{
    unsigned long *regs;

    pr_debug("ptrace_write_user(%s[%u], %#lx, %#lx)\n",
            tsk->comm, tsk->pid, offset, value);

    if (offset & 3 || offset >= sizeof(struct user)) {
        pr_debug("  invalid offset 0x%08lx\n", offset);
        return -EIO;
    }

    if (offset >= sizeof(struct pt_regs))
        return 0;

    regs = (unsigned long *)get_user_regs(tsk);
    regs[offset / sizeof(regs[0])] = value;

    return 0;
}

static int ptrace_getregs(struct task_struct *tsk, void __user *uregs)
{
    struct pt_regs *regs = get_user_regs(tsk);

    return copy_to_user(uregs, regs, sizeof(*regs)) ? -EFAULT : 0;
}

static int ptrace_setregs(struct task_struct *tsk, const void __user *uregs)
{
    struct pt_regs newregs;
    int ret;

    ret = -EFAULT;
    if (copy_from_user(&newregs, uregs, sizeof(newregs)) == 0) {
        struct pt_regs *regs = get_user_regs(tsk);

        ret = -EINVAL;
        if (valid_user_regs(&newregs)) {
            *regs = newregs;
            ret = 0;
        }
    }

    return ret;
}

long arch_ptrace(struct task_struct *child, long request,
         unsigned long addr, unsigned long data)
{
    int ret;
    void __user *datap = (void __user *) data;

    switch (request) {
    /* Read the word at location addr in the child process */
    case PTRACE_PEEKTEXT:
    case PTRACE_PEEKDATA:
        ret = generic_ptrace_peekdata(child, addr, data);
        break;

    case PTRACE_PEEKUSR:
        ret = ptrace_read_user(child, addr, datap);
        break;

    /* Write the word in data at location addr */
    case PTRACE_POKETEXT:
    case PTRACE_POKEDATA:
        ret = generic_ptrace_pokedata(child, addr, data);
        break;

    case PTRACE_POKEUSR:
        ret = ptrace_write_user(child, addr, data);
        break;

    case PTRACE_GETREGS:
        ret = ptrace_getregs(child, datap);
        break;

    case PTRACE_SETREGS:
        ret = ptrace_setregs(child, datap);
        break;

    default:
        ret = ptrace_request(child, request, addr, data);
        break;
    }

    return ret;
}

asmlinkage void syscall_trace(void)
{
    if (!test_thread_flag(TIF_SYSCALL_TRACE))
        return;
    if (!(current->ptrace & PT_PTRACED))
        return;

    /* The 0x80 provides a way for the tracing parent to
     * distinguish between a syscall stop and SIGTRAP delivery */
    ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
                 ? 0x80 : 0));

    /*
     * this isn't the same as continuing with a signal, but it
     * will do for normal use.  strace only continues with a
     * signal if the stopping signal is not SIGTRAP.  -brl
     */
    if (current->exit_code) {
        pr_debug("syscall_trace: sending signal %d to PID %u\n",
             current->exit_code, current->pid);
        send_sig(current->exit_code, current, 1);
        current->exit_code = 0;
    }
}

/*
 * debug_trampoline() is an assembly stub which will store all user
 * registers on the stack and execute a breakpoint instruction.
 *
 * If we single-step into an exception handler which runs with
 * interrupts disabled the whole time so it doesn't have to check for
 * pending work, its return address will be modified so that it ends
 * up returning to debug_trampoline.
 *
 * If the exception handler decides to store the user context and
 * enable interrupts after all, it will restore the original return
 * address and status register value. Before it returns, it will
 * notice that TIF_BREAKPOINT is set and execute a breakpoint
 * instruction.
 */
extern void debug_trampoline(void);

asmlinkage struct pt_regs *do_debug(struct pt_regs *regs)
{
    struct thread_info  *ti;
    unsigned long       trampoline_addr;
    u32         status;
    u32         ctrl;
    int         code;

    status = ocd_read(DS);
    ti = current_thread_info();
    code = TRAP_BRKPT;

    pr_debug("do_debug: status=0x%08x PC=0x%08lx SR=0x%08lx tif=0x%08lx\n",
            status, regs->pc, regs->sr, ti->flags);

    if (!user_mode(regs)) {
        unsigned long   die_val = DIE_BREAKPOINT;

        if (status & (1 << OCD_DS_SSS_BIT))
            die_val = DIE_SSTEP;

        if (notify_die(die_val, "ptrace", regs, 0, 0, SIGTRAP)
                == NOTIFY_STOP)
            return regs;

        if ((status & (1 << OCD_DS_SWB_BIT))
                && test_and_clear_ti_thread_flag(
                    ti, TIF_BREAKPOINT)) {
            /*
             * Explicit breakpoint from trampoline or
             * exception/syscall/interrupt handler.
             *
             * The real saved regs are on the stack right
             * after the ones we saved on entry.
             */
            regs++;
            pr_debug("  -> TIF_BREAKPOINT done, adjusted regs:"
                    "PC=0x%08lx SR=0x%08lx\n",
                    regs->pc, regs->sr);
            BUG_ON(!user_mode(regs));

            if (test_thread_flag(TIF_SINGLE_STEP)) {
                pr_debug("Going to do single step...\n");
                return regs;
            }

            /*
             * No TIF_SINGLE_STEP means we're done
             * stepping over a syscall. Do the trap now.
             */
            code = TRAP_TRACE;
        } else if ((status & (1 << OCD_DS_SSS_BIT))
                && test_ti_thread_flag(ti, TIF_SINGLE_STEP)) {

            pr_debug("Stepped into something, "
                    "setting TIF_BREAKPOINT...\n");
            set_ti_thread_flag(ti, TIF_BREAKPOINT);

            /*
             * We stepped into an exception, interrupt or
             * syscall handler. Some exception handlers
             * don't check for pending work, so we need to
             * set up a trampoline just in case.
             *
             * The exception entry code will undo the
             * trampoline stuff if it does a full context
             * save (which also means that it'll check for
             * pending work later.)
             */
            if ((regs->sr & MODE_MASK) == MODE_EXCEPTION) {
                trampoline_addr
                    = (unsigned long)&debug_trampoline;

                pr_debug("Setting up trampoline...\n");
                ti->rar_saved = sysreg_read(RAR_EX);
                ti->rsr_saved = sysreg_read(RSR_EX);
                sysreg_write(RAR_EX, trampoline_addr);
                sysreg_write(RSR_EX, (MODE_EXCEPTION
                            | SR_EM | SR_GM));
                BUG_ON(ti->rsr_saved & MODE_MASK);
            }

            /*
             * If we stepped into a system call, we
             * shouldn't do a single step after we return
             * since the return address is right after the
             * "scall" instruction we were told to step
             * over.
             */
            if ((regs->sr & MODE_MASK) == MODE_SUPERVISOR) {
                pr_debug("Supervisor; no single step\n");
                clear_ti_thread_flag(ti, TIF_SINGLE_STEP);
            }

            ctrl = ocd_read(DC);
            ctrl &= ~(1 << OCD_DC_SS_BIT);
            ocd_write(DC, ctrl);

            return regs;
        } else {
            printk(KERN_ERR "Unexpected OCD_DS value: 0x%08x\n",
                    status);
            printk(KERN_ERR "Thread flags: 0x%08lx\n", ti->flags);
            die("Unhandled debug trap in kernel mode",
                    regs, SIGTRAP);
        }
    } else if (status & (1 << OCD_DS_SSS_BIT)) {
        /* Single step in user mode */
        code = TRAP_TRACE;

        ctrl = ocd_read(DC);
        ctrl &= ~(1 << OCD_DC_SS_BIT);
        ocd_write(DC, ctrl);
    }

    pr_debug("Sending SIGTRAP: code=%d PC=0x%08lx SR=0x%08lx\n",
            code, regs->pc, regs->sr);

    clear_thread_flag(TIF_SINGLE_STEP);
    _exception(SIGTRAP, regs, code, instruction_pointer(regs));

    return regs;
}