kernel/ptrace.c

/* ptrace.c */
/* By Ross Biro 1/23/92 */
/* edited by Linus Torvalds */

#include <linux/head.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/errno.h>
#include <linux/ptrace.h>
#include <linux/user.h>

#include <asm/segment.h>
#include <asm/system.h>
#include <linux/debugreg.h>

/*
 * does not yet catch signals sent when the child dies.
 * in exit.c or in signal.c.
 */
//exit.c和signal.c当子进程退出时任然捕获不到信号
/* determines which flags the user has access to. */
/* 1 = access 0 = no access */
#define FLAG_MASK 0x00044dd5

/* set's the trap flag. */
#define TRAP_FLAG 0x100

/*
 * this is the number to subtract from the top of the stack. To find
 * the local frame.
 */
#define MAGICNUMBER 68

/* change a pid into a task struct. */
//获取指定pid的任务
static inline struct task_struct * get_task(int pid)
{
    int i;
    //遍历所有任务进程，查找指定进程号的进程
    for (i = 1; i < NR_TASKS; i++) {
        if (task[i] != NULL && (task[i]->pid == pid))
            return task[i];
    }
    return NULL;
}

/*
 * this routine will get a word off of the processes priviledged stack.
 * the offset is how far from the base addr as stored in the TSS.  
 * this routine assumes that all the priviledged stacks are in our
 * data space.
 */   
 //获取栈的偏移处的内容
static inline int get_stack_long(struct task_struct *task, int offset)
{
    unsigned char *stack;
    //获取到栈基址
    stack = (unsigned char *)task->tss.esp0;
    //计算偏移
    stack += offset;
    //取出该位置的内容
    return (*((int *)stack));
}

/*
 * this routine will put a word on the processes priviledged stack.
 * the offset is how far from the base addr as stored in the TSS.  
 * this routine assumes that all the priviledged stacks are in our
 * data space.
 */
 //设置栈指定偏移处的内容
static inline int put_stack_long(struct task_struct *task, int offset,
    unsigned long data)
{
    unsigned char * stack;
    //栈基址
    stack = (unsigned char *) task->tss.esp0;
    //偏移位置
    stack += offset;
    //设置内容
    *(unsigned long *) stack = data;
    return 0;
}

/*
 * This routine gets a long from any process space by following the page
 * tables. NOTE! You should check that the long isn't on a page boundary,
 * and that it is in the task area before calling this: this routine does
 * no checking.
 *
 * NOTE2! This uses "tsk->tss.cr3" even though we know it's currently always
 * zero. This routine shouldn't have to change when we make a better mm.
 */
 //获取指定任务的内存控制任意位置处的数据
static unsigned long get_long(struct task_struct * tsk,
    unsigned long addr)
{
    unsigned long page;

repeat:
    page = *PAGE_DIR_OFFSET(tsk->tss.cr3,addr);
    if (page & PAGE_PRESENT) {
        page &= PAGE_MASK;
        page += PAGE_PTR(addr);
        page = *((unsigned long *) page);
    }
    if (!(page & PAGE_PRESENT)) {
        do_no_page(0,addr,tsk,0);
        goto repeat;
    }
/* this is a hack for non-kernel-mapped video buffers and similar */
    if (page >= high_memory)
        return 0;
    page &= PAGE_MASK;
    page += addr & ~PAGE_MASK;
    return *(unsigned long *) page;
}

/*
 * This routine puts a long into any process space by following the page
 * tables. NOTE! You should check that the long isn't on a page boundary,
 * and that it is in the task area before calling this: this routine does
 * no checking.
 *
 * Now keeps R/W state of page so that a text page stays readonly
 * even if a debugger scribbles breakpoints into it.  -M.U-
 */
static void put_long(struct task_struct * tsk, unsigned long addr,
    unsigned long data)
{
    unsigned long page, pte = 0;
    int readonly = 0;

repeat:
    page = *PAGE_DIR_OFFSET(tsk->tss.cr3,addr);
    if (page & PAGE_PRESENT) {
        page &= PAGE_MASK;
        page += PAGE_PTR(addr);
        pte = page;
        page = *((unsigned long *) page);
    }
    if (!(page & PAGE_PRESENT)) {
        do_no_page(0 /* PAGE_RW */ ,addr,tsk,0);
        goto repeat;
    }
    if (!(page & PAGE_RW)) {
        if(!(page & PAGE_COW))
            readonly = 1;
        do_wp_page(PAGE_RW | PAGE_PRESENT,addr,tsk,0);
        goto repeat;
    }
/* this is a hack for non-kernel-mapped video buffers and similar */
    if (page >= high_memory)
        return;
/* we're bypassing pagetables, so we have to set the dirty bit ourselves */
    *(unsigned long *) pte |= (PAGE_DIRTY|PAGE_COW);
    page &= PAGE_MASK;
    page += addr & ~PAGE_MASK;
    *(unsigned long *) page = data;
    if(readonly) {
        *(unsigned long *) pte &=~ (PAGE_RW|PAGE_COW);
        invalidate();
    }
}

/*
 * This routine checks the page boundaries, and that the offset is
 * within the task area. It then calls get_long() to read a long.
 */
static int read_long(struct task_struct * tsk, unsigned long addr,
    unsigned long * result)
{
    unsigned long low,high;

if (addr > TASK_SIZE-sizeof(long))
        return -EIO;
    if ((addr & ~PAGE_MASK) > PAGE_SIZE-sizeof(long)) {
        low = get_long(tsk,addr & ~(sizeof(long)-1));
        high = get_long(tsk,(addr+sizeof(long)) & ~(sizeof(long)-1));
        switch (addr & (sizeof(long)-1)) {
            case 1:
                low >>= 8;
                low |= high << 24;
                break;
            case 2:
                low >>= 16;
                low |= high << 16;
                break;
            case 3:
                low >>= 24;
                low |= high << 8;
                break;
        }
        *result = low;
    } else
        *result = get_long(tsk,addr);
    return 0;
}

/*
 * This routine checks the page boundaries, and that the offset is
 * within the task area. It then calls put_long() to write a long.
 */
static int write_long(struct task_struct * tsk, unsigned long addr,
    unsigned long data)
{
    unsigned long low,high;

if (addr > TASK_SIZE-sizeof(long))
        return -EIO;
    if ((addr & ~PAGE_MASK) > PAGE_SIZE-sizeof(long)) {
        low = get_long(tsk,addr & ~(sizeof(long)-1));
        high = get_long(tsk,(addr+sizeof(long)) & ~(sizeof(long)-1));
        switch (addr & (sizeof(long)-1)) {
            case 0: /* shouldn't happen, but safety first */
                low = data;
                break;
            case 1:
                low &= 0x000000ff;
                low |= data << 8;
                high &= ~0xff;
                high |= data >> 24;
                break;
            case 2:
                low &= 0x0000ffff;
                low |= data << 16;
                high &= ~0xffff;
                high |= data >> 16;
                break;
            case 3:
                low &= 0x00ffffff;
                low |= data << 24;
                high &= ~0xffffff;
                high |= data >> 8;
                break;
        }
        put_long(tsk,addr & ~(sizeof(long)-1),low);
        put_long(tsk,(addr+sizeof(long)) & ~(sizeof(long)-1),high);
    } else
        put_long(tsk,addr,data);
    return 0;
}

asmlinkage int sys_ptrace(long request, long pid, long addr, long data)
{
    struct task_struct *child;
    struct user * dummy;
    int i;

dummy = NULL;

if (request == PTRACE_TRACEME) {
        /* are we already being traced? */
        if (current->flags & PF_PTRACED)
            return -EPERM;
        /* set the ptrace bit in the proccess flags. */
        current->flags |= PF_PTRACED;
        return 0;
    }
    if (pid == 1)        /* you may not mess with init */
        return -EPERM;
    if (!(child = get_task(pid)))
        return -ESRCH;
    if (request == PTRACE_ATTACH) {
        if (child == current)
            return -EPERM;
        if ((!child->dumpable || (current->uid != child->euid) ||
             (current->gid != child->egid)) && !suser())
            return -EPERM;
        /* the same process cannot be attached many times */
        if (child->flags & PF_PTRACED)
            return -EPERM;
        child->flags |= PF_PTRACED;
        if (child->p_pptr != current) {
            REMOVE_LINKS(child);
            child->p_pptr = current;
            SET_LINKS(child);
        }
        send_sig(SIGSTOP, child, 1);
        return 0;
    }
    if (!(child->flags & PF_PTRACED))
        return -ESRCH;
    if (child->state != TASK_STOPPED) {
        if (request != PTRACE_KILL)
            return -ESRCH;
    }
    if (child->p_pptr != current)
        return -ESRCH;

switch (request) {
    /* when I and D space are seperate, these will need to be fixed. */
        case PTRACE_PEEKTEXT: /* read word at location addr. */
        case PTRACE_PEEKDATA: {
            unsigned long tmp;
            int res;

res = read_long(child, addr, &tmp);
            if (res < 0)
                return res;
            res = verify_area(VERIFY_WRITE, (void *) data, sizeof(long));
            if (!res)
                put_fs_long(tmp,(unsigned long *) data);
            return res;
        }

/* read the word at location addr in the USER area. */
        case PTRACE_PEEKUSR: {
            unsigned long tmp;
            int res;

if ((addr & 3) || addr < 0 ||
                addr > sizeof(struct user) - 3)
                return -EIO;

res = verify_area(VERIFY_WRITE, (void *) data, sizeof(long));
            if (res)
                return res;
            tmp = 0;  /* Default return condition */
            if(addr < 17*sizeof(long)) {
              addr = addr >> 2; /* temporary hack. */

tmp = get_stack_long(child, sizeof(long)*addr - MAGICNUMBER);
              if (addr == DS || addr == ES ||
                  addr == FS || addr == GS ||
                  addr == CS || addr == SS)
                tmp &= 0xffff;
            };
            if(addr >= (long) &dummy->u_debugreg[0] &&
               addr <= (long) &dummy->u_debugreg[7]){
                addr -= (long) &dummy->u_debugreg[0];
                addr = addr >> 2;
                tmp = child->debugreg[addr];
            };
            put_fs_long(tmp,(unsigned long *) data);
            return 0;
        }

/* when I and D space are seperate, this will have to be fixed. */
        case PTRACE_POKETEXT: /* write the word at location addr. */
        case PTRACE_POKEDATA:
            return write_long(child,addr,data);

case PTRACE_POKEUSR: /* write the word at location addr in the USER area */
            if ((addr & 3) || addr < 0 ||
                addr > sizeof(struct user) - 3)
                return -EIO;

addr = addr >> 2; /* temproary hack. */

if (addr == ORIG_EAX)
                return -EIO;
            if (addr == DS || addr == ES ||
                addr == FS || addr == GS ||
                addr == CS || addr == SS) {
                    data &= 0xffff;
                    if (data && (data & 3) != 3)
                    return -EIO;
            }
            if (addr == EFL) {   /* flags. */
                data &= FLAG_MASK;
                data |= get_stack_long(child, EFL*sizeof(long)-MAGICNUMBER)  & ~FLAG_MASK;
            }
          /* Do not allow the user to set the debug register for kernel
             address space */
          if(addr < 17){
              if (put_stack_long(child, sizeof(long)*addr-MAGICNUMBER, data))
                return -EIO;
            return 0;
            };

/* We need to be very careful here.  We implicitly
             want to modify a portion of the task_struct, and we
             have to be selective about what portions we allow someone
             to modify. */

addr = addr << 2;  /* Convert back again */
          if(addr >= (long) &dummy->u_debugreg[0] &&
             addr <= (long) &dummy->u_debugreg[7]){

if(addr == (long) &dummy->u_debugreg[4]) return -EIO;
              if(addr == (long) &dummy->u_debugreg[5]) return -EIO;
              if(addr < (long) &dummy->u_debugreg[4] &&
                 ((unsigned long) data) >= 0xbffffffd) return -EIO;
              
              if(addr == (long) &dummy->u_debugreg[7]) {
                  data &= ~DR_CONTROL_RESERVED;
                  for(i=0; i<4; i++)
                      if ((0x5f54 >> ((data >> (16 + 4*i)) & 0xf)) & 1)
                          return -EIO;
              };

addr -= (long) &dummy->u_debugreg;
              addr = addr >> 2;
              child->debugreg[addr] = data;
              return 0;
          };
          return -EIO;

case PTRACE_SYSCALL: /* continue and stop at next (return from) syscall */
        case PTRACE_CONT: { /* restart after signal. */
            long tmp;

if ((unsigned long) data > NSIG)
                return -EIO;
            if (request == PTRACE_SYSCALL)
                child->flags |= PF_TRACESYS;
            else
                child->flags &= ~PF_TRACESYS;
            child->exit_code = data;
            child->state = TASK_RUNNING;
    /* make sure the single step bit is not set. */
            tmp = get_stack_long(child, sizeof(long)*EFL-MAGICNUMBER) & ~TRAP_FLAG;
            put_stack_long(child, sizeof(long)*EFL-MAGICNUMBER,tmp);
            return 0;
        }

/*
 * make the child exit.  Best I can do is send it a sigkill.
 * perhaps it should be put in the status that it want's to
 * exit.
 */
        case PTRACE_KILL: {
            long tmp;

child->state = TASK_RUNNING;
            child->exit_code = SIGKILL;
    /* make sure the single step bit is not set. */
            tmp = get_stack_long(child, sizeof(long)*EFL-MAGICNUMBER) & ~TRAP_FLAG;
            put_stack_long(child, sizeof(long)*EFL-MAGICNUMBER,tmp);
            return 0;
        }

case PTRACE_SINGLESTEP: {  /* set the trap flag. */
            long tmp;

if ((unsigned long) data > NSIG)
                return -EIO;
            child->flags &= ~PF_TRACESYS;
            tmp = get_stack_long(child, sizeof(long)*EFL-MAGICNUMBER) | TRAP_FLAG;
            put_stack_long(child, sizeof(long)*EFL-MAGICNUMBER,tmp);
            child->state = TASK_RUNNING;
            child->exit_code = data;
    /* give it a chance to run. */
            return 0;
        }

case PTRACE_DETACH: { /* detach a process that was attached. */
            long tmp;

if ((unsigned long) data > NSIG)
                return -EIO;
            child->flags &= ~(PF_PTRACED|PF_TRACESYS);
            child->state = TASK_RUNNING;
            child->exit_code = data;
            REMOVE_LINKS(child);
            child->p_pptr = child->p_opptr;
            SET_LINKS(child);
            /* make sure the single step bit is not set. */
            tmp = get_stack_long(child, sizeof(long)*EFL-MAGICNUMBER) & ~TRAP_FLAG;
            put_stack_long(child, sizeof(long)*EFL-MAGICNUMBER,tmp);
            return 0;
        }

default:
            return -EIO;
    }
}

//系统调用
asmlinkage void syscall_trace(void)
{
    if ((current->flags & (PF_PTRACED|PF_TRACESYS))
            != (PF_PTRACED|PF_TRACESYS))
        return;
    current->exit_code = SIGTRAP;
    current->state = TASK_STOPPED;
    notify_parent(current);
    schedule();
    /*
     * 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)
        current->signal |= (1 << (current->exit_code - 1));
    current->exit_code = 0;
}