[PATCH] kretprobe: fix kretprobe-booster to save regs and set status

There are two bugs in the kretprobe-booster.

1) It doesn't make room for gs registers.

2) It doesn't change status of the current kprobe.  This status will
   effect the fault handling.

This patch fixes these bugs and, additionally, saves skipped registers for
compatibility with the original kretprobe.
Signed-off-by: NMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

arch/i386/kernel/kprobes.c

@@ -361,8 +361,11 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
 	asm volatile ( ".global kretprobe_trampoline\n"
 			"kretprobe_trampoline: \n"
 			"	pushf\n"
-			/* skip cs, eip, orig_eax, es, ds */
-			"	subl $20, %esp\n"
+			/* skip cs, eip, orig_eax */
+			"	subl $12, %esp\n"
+			"	pushl %gs\n"
+			"	pushl %ds\n"
+			"	pushl %es\n"
 			"	pushl %eax\n"
 			"	pushl %ebp\n"
 			"	pushl %edi\n"
@@ -373,10 +376,10 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
 			"	movl %esp, %eax\n"
 			"	call trampoline_handler\n"
 			/* move eflags to cs */
-			"	movl 48(%esp), %edx\n"
-			"	movl %edx, 44(%esp)\n"
+			"	movl 52(%esp), %edx\n"
+			"	movl %edx, 48(%esp)\n"
 			/* save true return address on eflags */
-			"	movl %eax, 48(%esp)\n"
+			"	movl %eax, 52(%esp)\n"
 			"	popl %ebx\n"
 			"	popl %ecx\n"
 			"	popl %edx\n"
@@ -384,8 +387,8 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
 			"	popl %edi\n"
 			"	popl %ebp\n"
 			"	popl %eax\n"
-			/* skip eip, orig_eax, es, ds */
-			"	addl $16, %esp\n"
+			/* skip eip, orig_eax, es, ds, gs */
+			"	addl $20, %esp\n"
 			"	popf\n"
 			"	ret\n");
 }
@@ -404,6 +407,10 @@ fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)
 	INIT_HLIST_HEAD(&empty_rp);
 	spin_lock_irqsave(&kretprobe_lock, flags);
 	head = kretprobe_inst_table_head(current);
+	/* fixup registers */
+	regs->xcs = __KERNEL_CS;
+	regs->eip = trampoline_address;
+	regs->orig_eax = 0xffffffff;
 
 	/*
 	 * It is possible to have multiple instances associated with a given
@@ -425,6 +432,7 @@ fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)
 
 		if (ri->rp && ri->rp->handler){
 			__get_cpu_var(current_kprobe) = &ri->rp->kp;
+			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 			ri->rp->handler(ri, regs);
 			__get_cpu_var(current_kprobe) = NULL;
 		}