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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;
}