[FIX] Save current uprobe state in stack (x86)

We cannot use per cpu vars here because when we make a singlestep
in userspace there is a chance our task is preempted and resumed
on another cpu. In that case we will not be able to restore its
normal execution.

Change-Id: I591ef52b52db8db0e741d81461903806ed00ef8e
Signed-off-by: Vyacheslav Cherkashin <v.cherkashin@samsung.com>
Signed-off-by: Vasiliy Ulyanov <v.ulyanov@samsung.com>

1 files changed, 46 insertions, 26 deletions

diff --git a/uprobe/arch/x86/swap-asm/swap_uprobes.c b/uprobe/arch/x86/swap-asm/swap_uprobes.c
index 1b0fbe8e..f4f2272a 100644
--- a/uprobe/arch/x86/swap-asm/swap_uprobes.c
+++ b/uprobe/arch/x86/swap-asm/swap_uprobes.c
@@ -54,32 +54,31 @@ static unsigned long trampoline_addr(struct uprobe *up)
 			       UPROBES_TRAMP_RET_BREAK_IDX);
 }
 
-static DEFINE_PER_CPU(struct uprobe_ctlblk, ucb) = { 0, NULL };
-
-static struct kprobe *get_current_probe(void)
+static struct uprobe_ctlblk *current_ucb(void)
 {
-	return __get_cpu_var(ucb).p;
+	/* FIXME hardcoded offset */
+	return (struct uprobe_ctlblk *)(end_of_stack(current) + 20);
 }
 
-static void set_current_probe(struct kprobe *p)
+static struct kprobe *get_current_probe(void)
 {
-	__get_cpu_var(ucb).p = p;
+	return current_ucb()->p;
 }
 
-static void reset_current_probe(void)
+static void set_current_probe(struct kprobe *p)
 {
-	set_current_probe(NULL);
+	current_ucb()->p = p;
 }
 
 static void save_current_flags(struct pt_regs *regs)
 {
-	__get_cpu_var(ucb).flags = regs->EREG(flags);
+	current_ucb()->flags = regs->flags;
 }
 
-static void restore_current_flags(struct pt_regs *regs)
+static void restore_current_flags(struct pt_regs *regs, unsigned long flags)
 {
-	regs->EREG(flags) &= ~IF_MASK;
-	regs->EREG(flags) |= __get_cpu_var(ucb).flags & IF_MASK;
+	regs->flags &= ~IF_MASK;
+	regs->flags |= flags & IF_MASK;
 }
 
 /**
@@ -420,6 +419,27 @@ no_change:
 	return;
 }
 
+static bool prepare_ss_addr(struct kprobe *p, struct pt_regs *regs)
+{
+	unsigned long *ss_addr = (long *)&p->ss_addr[smp_processor_id()];
+
+	if (*ss_addr) {
+		regs->ip = *ss_addr;
+		*ss_addr = 0;
+		return true;
+	} else {
+		regs->ip = (unsigned long)p->ainsn.insn;
+		return false;
+	}
+}
+
+static void prepare_ss(struct pt_regs *regs)
+{
+	/* set single step mode */
+	regs->flags |= TF_MASK;
+	regs->flags &= ~IF_MASK;
+}
+
 static int uprobe_handler(struct pt_regs *regs)
 {
 	struct kprobe *p;
@@ -445,38 +465,38 @@ static int uprobe_handler(struct pt_regs *regs)
 		return 1;
 	} else {
 		if (!p->pre_handler || !p->pre_handler(p, regs)) {
-
 			if (p->ainsn.boostable == 1 && !p->post_handler) {
-				if (p->ss_addr[smp_processor_id()]) {
-					regs->EREG(ip) = (unsigned long)p->ss_addr[smp_processor_id()];
-					p->ss_addr[smp_processor_id()] = NULL;
-				} else {
-					regs->EREG(ip) = (unsigned long)p->ainsn.insn;
-				}
+				prepare_ss_addr(p, regs);
 				return 1;
 			}
 
-			prepare_singlestep(p, regs);
+			if (prepare_ss_addr(p, regs) == false) {
+				set_current_probe(p);
+				prepare_ss(regs);
+			}
 		}
 	}
 
-	set_current_probe(p);
-
 	return 1;
 }
 
 static int post_uprobe_handler(struct pt_regs *regs)
 {
 	struct kprobe *p = get_current_probe();
-	unsigned long flags = __get_cpu_var(ucb).flags;
+	unsigned long flags = current_ucb()->flags;
 
-	if (p == NULL)
+	if (p == NULL) {
+		printk("task[%u %u %s] current uprobe is not found\n",
+		       current->tgid, current->pid, current->comm);
 		return 0;
+	}
 
 	resume_execution(p, regs, flags);
-	restore_current_flags(regs);
+	restore_current_flags(regs, flags);
 
-	reset_current_probe();
+	/* clean stack */
+	current_ucb()->p = 0;
+	current_ucb()->flags = 0;
 
 	return 1;
 }