ptrace.c

来自「自己根据lkd和情境分析」· C语言 代码 · 共 464 行

/* ptrace.c */
/* By Ross Biro 1/23/92 */
/*
 * Pentium III FXSR, SSE support
 *	Gareth Hughes <[e-mail]>, May 2000
 */

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

#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/system.h>
#include <asm/processor.h>
#include <asm/i387.h>
#include <asm/debugreg.h>

/*
 * does not yet catch signals sent when the child dies.
 * in exit.c or in signal.c.
 */

/* 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   /*硬件标志位，它是处理器中的"标志位寄存器"EFL的一位，设为1时，处理器在每执行完一条机器指令后就进入debug陷阱而到达一个断点*/

/*
 * Offset of eflags on child stack..
 */
#define EFL_OFFSET ((EFL-2)*4-sizeof(struct pt_regs))

/*
 * this routine will get a word off of the processes privileged stack. 
 * the offset is how far from the base addr as stored in the TSS.  
 * this routine assumes that all the privileged stacks are in our
 * data space.
 */   
static inline int get_stack_long(struct task_struct *task, int offset)
{
	unsigned char *stack;

	stack = (unsigned char *)task->thread.esp0;
	stack += offset;
	return (*((int *)stack));
}

/*
 * this routine will put a word on the processes privileged stack. 
 * the offset is how far from the base addr as stored in the TSS.  
 * this routine assumes that all the privileged stacks are in our
 * data space.
 */
static inline int put_stack_long(struct task_struct *task, int offset,
	unsigned long data)
{
	unsigned char * stack;

	stack = (unsigned char *) task->thread.esp0;
	stack += offset;
	*(unsigned long *) stack = data;
	return 0;
}

static int putreg(struct task_struct *child,
	unsigned long regno, unsigned long value)
{
	switch (regno >> 2) {
		case FS:
			if (value && (value & 3) != 3)
				return -EIO;
			child->thread.fs = value;
			return 0;
		case GS:
			if (value && (value & 3) != 3)
				return -EIO;
			child->thread.gs = value;
			return 0;
		case DS:
		case ES:
			if (value && (value & 3) != 3)
				return -EIO;
			value &= 0xffff;
			break;
		case SS:
		case CS:
			if ((value & 3) != 3)
				return -EIO;
			value &= 0xffff;
			break;
		case EFL:
			value &= FLAG_MASK;
			value |= get_stack_long(child, EFL_OFFSET) & ~FLAG_MASK;
			break;
	}
	if (regno > GS*4)
		regno -= 2*4;
	put_stack_long(child, regno - sizeof(struct pt_regs), value);
	return 0;
}

static unsigned long getreg(struct task_struct *child,
	unsigned long regno)
{
	unsigned long retval = ~0UL;

	switch (regno >> 2) {
		case FS:
			retval = child->thread.fs;
			break;
		case GS:
			retval = child->thread.gs;
			break;
		case DS:
		case ES:
		case SS:
		case CS:
			retval = 0xffff;
			/* fall through */
		default:
			if (regno > GS*4)
				regno -= 2*4;
			regno = regno - sizeof(struct pt_regs);
			retval &= get_stack_long(child, regno);
	}
	return retval;
}

/*
 * Called by kernel/ptrace.c when detaching..
 *
 * Make sure the single step bit is not set.
 */
void ptrace_disable(struct task_struct *child)
{ 
	long tmp;

	tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
	put_stack_long(child, EFL_OFFSET, tmp);
}

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

	lock_kernel();
	ret = -EPERM;
	if (request == PTRACE_TRACEME) {
		/* are we already being traced? */
		if (current->ptrace & PT_PTRACED)
			goto out;
		/* set the ptrace bit in the process flags. */
		current->ptrace |= PT_PTRACED;
		ret = 0;
		goto out;
	}
	ret = -ESRCH;
	read_lock(&tasklist_lock);
	child = find_task_by_pid(pid);
	if (child)
		get_task_struct(child);
	read_unlock(&tasklist_lock);
	if (!child)
		goto out;

	ret = -EPERM;
	if (pid == 1)		/* you may not mess with init */
		goto out_tsk;

	if (request == PTRACE_ATTACH) {
		ret = ptrace_attach(child);
		goto out_tsk;
	}

	ret = ptrace_check_attach(child, request == PTRACE_KILL);
	if (ret < 0)
		goto out_tsk;

	switch (request) {
	/* when I and D space are separate, these will need to be fixed. */
	case PTRACE_PEEKTEXT: /* read word at location addr. 操作从子进程的指令空间，或称代码段地址为addr处读取一个长字*/ 
	case PTRACE_PEEKDATA: {   /*从子进程的数据空间读一个长字，linux内核中代码空间和数据空间实际上是一致的，所以并在一起处理*/
		unsigned long tmp;        /*PTRACE_PEEKDATA和PTRACE_PEEKTEXT只能用来读子进程的用户空间，而不能用来读系统空间，这是由find_extend_vma保证的*/
		int copied;

		copied = access_process_vm(child, addr, &tmp, sizeof(tmp), 0);
		ret = -EIO;
		if (copied != sizeof(tmp))
			break;
		ret = put_user(tmp,(unsigned long *) data);
		break;
	}

	/* read the word at location addr in the USER area. */
	case PTRACE_PEEKUSR: {  /*1)用于读取子进程在用户空间运行时的(进入系统空间前夕)的某个寄存器的内容(注意此时子进程必定在系统空间中，因为调度和切换只发生于系统空间)， 2)引入调试寄存器，用户进程可以通过设置一些调试寄存器来使处理器在一定的条件下落入陷阱，从而进入一个断点，即一段调试程序，这些条件包括:a)当处理器执行到某一指令时，b)当处理器读某一内存地址时，c)从处理器写某一内存地址时。而陷阱则是指专门用于虚拟地址模式程序调试的1号陷阱debug(另有一个用于实地址模式的3号陷阱int3，在linux中仅用于vm86模式)*/
		unsigned long tmp;
		/*要读取一个寄存器的内容时，参数addr必须是寄存器号乘以4，对于i386有17个这样的寄存器*/
		ret = -EIO;
		if ((addr & 3) || addr < 0 || 
		    addr > sizeof(struct user) - 3)
			break;

		tmp = 0;  /* Default return condition */
		if(addr < FRAME_SIZE*sizeof(long))
			tmp = getreg(child, addr);
		if(addr >= (long) &dummy->u_debugreg[0] &&
		   addr <= (long) &dummy->u_debugreg[7]){   /*检查addr的范围，假定一个user结构是从地址0开始的，看addr的值是否对应于该结构中u_debugreg[]数组的偏移量*/
			addr -= (long) &dummy->u_debugreg[0];
			addr = addr >> 2;
			tmp = child->thread.debugreg[addr];
		}
		ret = put_user(tmp,(unsigned long *) data);
		break;
	}

	/* when I and D space are separate, this will have to be fixed. */
	case PTRACE_POKETEXT: /* write the word at location addr. */
	case PTRACE_POKEDATA:
		ret = 0;
		if (access_process_vm(child, addr, &data, sizeof(data), 1) == sizeof(data))
			break;
		ret = -EIO;
		break;

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

		if (addr < FRAME_SIZE*sizeof(long)) {
			ret = putreg(child, addr, data);
			break;
		}
		/* 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. */

		  ret = -EIO;
		  if(addr >= (long) &dummy->u_debugreg[0] &&
		     addr <= (long) &dummy->u_debugreg[7]){  /*调试寄存器0至3这四个寄存器是允许设置的，但要检查所设置的值data(实际上是个内存地址)是否越出了用户空间的范围，除此之外只有调度寄存器7是允许设置的，但对其数值有些特殊的要求*/

			  if(addr == (long) &dummy->u_debugreg[4]) break;
			  if(addr == (long) &dummy->u_debugreg[5]) break;
			  if(addr < (long) &dummy->u_debugreg[4] &&
			     ((unsigned long) data) >= TASK_SIZE-3) break;
			  
			  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)
						  goto out_tsk;
			  }

			  addr -= (long) &dummy->u_debugreg;
			  addr = addr >> 2;
			  child->thread.debugreg[addr] = data;
			  ret = 0;
		  }
		  break;

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

		ret = -EIO;
		if ((unsigned long) data > _NSIG)
			break;
		if (request == PTRACE_SYSCALL)
			child->ptrace |= PT_TRACESYS;
		else
			child->ptrace &= ~PT_TRACESYS;
		child->exit_code = data;
	/* make sure the single step bit is not set. 由于使子进程在下一次进入系统调用时暂停与使子进程在执行下一条指令后暂停(PTRACE_SINGLESTEP)是互斥的*/
		tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
		put_stack_long(child, EFL_OFFSET,tmp);
		wake_up_process(child);
		ret = 0;
		break;
	}

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

		ret = 0;
		if (child->state == TASK_ZOMBIE)	/* already dead */
			break;
		child->exit_code = SIGKILL;
		/* make sure the single step bit is not set. */
		tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
		put_stack_long(child, EFL_OFFSET, tmp);
		wake_up_process(child);
		break;
	}

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

		ret = -EIO;
		if ((unsigned long) data > _NSIG)
			break;
		child->ptrace &= ~PT_TRACESYS;
		if ((child->ptrace & PT_DTRACE) == 0) {
			/* Spurious delayed TF traps may occur */
			child->ptrace |= PT_DTRACE;
		}
		tmp = get_stack_long(child, EFL_OFFSET) | TRAP_FLAG;
		put_stack_long(child, EFL_OFFSET, tmp);
		child->exit_code = data;
		/* give it a chance to run. */
		wake_up_process(child);
		ret = 0;
		break;
	}

	case PTRACE_DETACH:
		/* detach a process that was attached. */
		ret = ptrace_detach(child, data);
		break;

	case PTRACE_GETREGS: { /* Get all gp regs from the child. */
	  	if (!access_ok(VERIFY_WRITE, (unsigned *)data, FRAME_SIZE*sizeof(long))) {
			ret = -EIO;
			break;
		}
		for ( i = 0; i < FRAME_SIZE*sizeof(long); i += sizeof(long) ) {
			__put_user(getreg(child, i),(unsigned long *) data);
			data += sizeof(long);
		}
		ret = 0;
		break;
	}

	case PTRACE_SETREGS: { /* Set all gp regs in the child. */
		unsigned long tmp;
	  	if (!access_ok(VERIFY_READ, (unsigned *)data, FRAME_SIZE*sizeof(long))) {
			ret = -EIO;
			break;
		}
		for ( i = 0; i < FRAME_SIZE*sizeof(long); i += sizeof(long) ) {
			__get_user(tmp, (unsigned long *) data);
			putreg(child, i, tmp);
			data += sizeof(long);
		}
		ret = 0;
		break;
	}

	case PTRACE_GETFPREGS: { /* Get the child FPU state. */
		if (!access_ok(VERIFY_WRITE, (unsigned *)data,
			       sizeof(struct user_i387_struct))) {
			ret = -EIO;
			break;
		}
		ret = 0;
		if ( !child->used_math ) {
			/* Simulate an empty FPU. */
			set_fpu_cwd(child, 0x037f);
			set_fpu_swd(child, 0x0000);
			set_fpu_twd(child, 0xffff);
		}
		get_fpregs((struct user_i387_struct *)data, child);
		break;
	}

	case PTRACE_SETFPREGS: { /* Set the child FPU state. */
		if (!access_ok(VERIFY_READ, (unsigned *)data,
			       sizeof(struct user_i387_struct))) {
			ret = -EIO;
			break;
		}
		child->used_math = 1;
		set_fpregs(child, (struct user_i387_struct *)data);
		ret = 0;
		break;
	}

	case PTRACE_GETFPXREGS: { /* Get the child extended FPU state. */
		if (!access_ok(VERIFY_WRITE, (unsigned *)data,
			       sizeof(struct user_fxsr_struct))) {
			ret = -EIO;
			break;
		}
		if ( !child->used_math ) {
			/* Simulate an empty FPU. */
			set_fpu_cwd(child, 0x037f);
			set_fpu_swd(child, 0x0000);
			set_fpu_twd(child, 0xffff);
			set_fpu_mxcsr(child, 0x1f80);
		}
		ret = get_fpxregs((struct user_fxsr_struct *)data, child);
		break;
	}

	case PTRACE_SETFPXREGS: { /* Set the child extended FPU state. */
		if (!access_ok(VERIFY_READ, (unsigned *)data,
			       sizeof(struct user_fxsr_struct))) {
			ret = -EIO;
			break;
		}
		child->used_math = 1;
		ret = set_fpxregs(child, (struct user_fxsr_struct *)data);
		break;
	}

	case PTRACE_SETOPTIONS: {
		if (data & PTRACE_O_TRACESYSGOOD)
			child->ptrace |= PT_TRACESYSGOOD;
		else
			child->ptrace &= ~PT_TRACESYSGOOD;
		ret = 0;
		break;
	}

	default:
		ret = -EIO;
		break;
	}
out_tsk:
	free_task_struct(child);
out:
	unlock_kernel();
	return ret;
}

asmlinkage void syscall_trace(void)
{
	if ((current->ptrace & (PT_PTRACED|PT_TRACESYS)) !=
			(PT_PTRACED|PT_TRACESYS))
		return;
	/* the 0x80 provides a way for the tracing parent to distinguish
	   between a syscall stop and SIGTRAP delivery */
	current->exit_code = SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
					? 0x80 : 0);
	current->state = TASK_STOPPED;
	notify_parent(current, SIGCHLD);
	schedule();  /*进入暂停状态，此时其父进程必定已经设置好对SIGCHLD信号的反应，当父进程设置了子进程的PT_TRACESS标志位，然后又接收到子进程发送过来的SIGCHLD信号时就知道子进程已经在系统调用的入口陷入了暂停状态，这时父进程就可以通过PTRACE_PEEKUSR等操作来收集或改变有关的数据，然后通过向子进程发送一个SIGCONT信号让它继续允许，也就是让它从syscall_trace()中的schedule()返回*/
	/*
	 * 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) {
		send_sig(current->exit_code, current, 1);
		current->exit_code = 0;
	}
}