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Commit 8701ea95 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Linus Torvalds
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[PATCH] ptrace: Fix EFL_OFFSET value according to i386 pda changes 



The PDA patches introduced a bug in ptrace: it reads eflags from the wrong
place on the target's stack, but writes it back to the correct place.  The
result is a corrupted eflags, which is most visible when it turns interrupts
off unexpectedly.

This patch fixes this by making the ptrace code a little less fragile.  It
changes [gs]et_stack_long to take a straightforward byte offset into struct
pt_regs, rather than requiring all callers to do a sizeof(struct pt_regs)
offset adjustment.  This means that the eflag's offset (EFL_OFFSET) on the
target stack can be simply computed with offsetof().

Signed-off-by: default avatarJeremy Fitzhardinge <jeremy@xensource.com>
Cc: Frederik Deweerdt <deweerdt@free.fr>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 7c7e9425

arch/i386/kernel/ptrace.c

+10 −11
Original line number Diff line number Diff line
@@ -45,7 +45,7 @@ 
/*

 * Offset of eflags on child stack..

 */

#define EFL_OFFSET ((EFL-2)*4-sizeof(struct pt_regs))

#define EFL_OFFSET offsetof(struct pt_regs, eflags)



static inline struct pt_regs *get_child_regs(struct task_struct *task)

{
@@ -54,24 +54,24 @@ static inline struct pt_regs *get_child_regs(struct task_struct *task) 
}



/*

 * 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

 * This routine will get a word off of the processes privileged stack.

 * the offset is bytes into the pt_regs structure on the stack.

 * 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 = (unsigned char *)task->thread.esp0 - sizeof(struct pt_regs);

	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

 * This routine will put a word on the processes privileged stack.

 * the offset is bytes into the pt_regs structure on the stack.

 * 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,
@@ -79,7 +79,7 @@ static inline int put_stack_long(struct task_struct *task, int offset, 
{

	unsigned char * stack;



	stack = (unsigned char *) task->thread.esp0;

	stack = (unsigned char *)task->thread.esp0 - sizeof(struct pt_regs);

	stack += offset;

	*(unsigned long *) stack = data;

	return 0;
@@ -114,7 +114,7 @@ static int putreg(struct task_struct *child, 
	}

	if (regno > ES*4)

		regno -= 1*4;

	put_stack_long(child, regno - sizeof(struct pt_regs), value);

	put_stack_long(child, regno, value);

	return 0;

}
@@ -137,7 +137,6 @@ static unsigned long getreg(struct task_struct *child, 
		default:

			if (regno > ES*4)

				regno -= 1*4;

			regno = regno - sizeof(struct pt_regs);

			retval &= get_stack_long(child, regno);

	}

	return retval;