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Commit c9becf58 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Linus Torvalds
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[PATCH] kretprobe: kretprobe-booster 



In normal operation, kretprobe makes a target function return to trampoline
code.  A kprobe (called trampoline_probe) has been inserted in the trampoline
code.  When the kernel hits this kprobe, it calls kretprobe's handler and it
returns to the original return address.

Kretprobe-booster removes the trampoline_probe.  It allows the trampoline code
to call kretprobe's handler directly instead of invoking kprobe.  The
trampoline code returns to the original return address.

(changelog from Chuck Ebbert <76306.1226@compuserve.com> - thanks ;))

Signed-off-by: default avatarMasami Hiramatsu <hiramatu@sdl.hitachi.co.jp>
Cc: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 311ac88f

arch/i386/kernel/kprobes.c

+39 −22
Original line number Diff line number Diff line
@@ -333,17 +333,44 @@ static int __kprobes kprobe_handler(struct pt_regs *regs) 
 * here. When a retprobed function returns, this probe is hit and

 * trampoline_probe_handler() runs, calling the kretprobe's handler.

 */

 void kretprobe_trampoline_holder(void)

 void __kprobes kretprobe_trampoline_holder(void)

 {

	asm volatile ( ".global kretprobe_trampoline\n"

 			"kretprobe_trampoline: \n"

 			"nop\n");

			"	pushf\n"

			/* skip cs, eip, orig_eax, es, ds */

			"	subl $20, %esp\n"

			"	pushl %eax\n"

			"	pushl %ebp\n"

			"	pushl %edi\n"

			"	pushl %esi\n"

			"	pushl %edx\n"

			"	pushl %ecx\n"

			"	pushl %ebx\n"

			"	movl %esp, %eax\n"

			"	call trampoline_handler\n"

			/* move eflags to cs */

			"	movl 48(%esp), %edx\n"

			"	movl %edx, 44(%esp)\n"

			/* save true return address on eflags */

			"	movl %eax, 48(%esp)\n"

			"	popl %ebx\n"

			"	popl %ecx\n"

			"	popl %edx\n"

			"	popl %esi\n"

			"	popl %edi\n"

			"	popl %ebp\n"

			"	popl %eax\n"

			/* skip eip, orig_eax, es, ds */

			"	addl $16, %esp\n"

			"	popf\n"

			"	ret\n");

}



/*

 * Called when we hit the probe point at kretprobe_trampoline

 * Called from kretprobe_trampoline

 */

int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)

fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)

{

        struct kretprobe_instance *ri = NULL;

        struct hlist_head *head;
@@ -372,8 +399,11 @@ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs) 
			/* another task is sharing our hash bucket */

                        continue;



		if (ri->rp && ri->rp->handler)

		if (ri->rp && ri->rp->handler){

			__get_cpu_var(current_kprobe) = &ri->rp->kp;

			ri->rp->handler(ri, regs);

			__get_cpu_var(current_kprobe) = NULL;

		}



		orig_ret_address = (unsigned long)ri->ret_addr;

		recycle_rp_inst(ri);
@@ -388,18 +418,10 @@ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs) 
	}



	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));

	regs->eip = orig_ret_address;



	reset_current_kprobe();

	spin_unlock_irqrestore(&kretprobe_lock, flags);

	preempt_enable_no_resched();



	/*

	 * By returning a non-zero value, we are telling

	 * kprobe_handler() that we don't want the post_handler

	 * to run (and have re-enabled preemption)

	 */

        return 1;

	return (void*)orig_ret_address;

}



/*
@@ -646,12 +668,7 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) 
	return 0;

}



static struct kprobe trampoline_p = {

	.addr = (kprobe_opcode_t *) &kretprobe_trampoline,

	.pre_handler = trampoline_probe_handler

};



int __init arch_init_kprobes(void)

{

	return register_kprobe(&trampoline_p);

	return 0;

}