[PATCH 2/4] arm64: Extract kprobes_save_local_irqflag() and kprobes_restore_local_irqflag()

[Wei Li]

PSTATE.I and PSTATE.D are very important for single-step working.

Without disabling interrupt on local CPU, there is a chance of
interrupt occurrence in the period of exception return and start of
out-of-line single-step, that result in wrongly single stepping
into the interrupt handler. And if D bit is set then, it results into
undefined exception and when it's handler enables dbg then single-step
exception is generated, not as expected.

As they are maintained well in kprobes_save_local_irqflag() and
kprobes_restore_local_irqflag() for kprobe module, extract them as
kernel_prepare_single_step() and kernel_cleanup_single_step() for
general use.

Signed-off-by: Wei Li <liwei391@xxxxxxxxxx>
---
 arch/arm64/include/asm/debug-monitors.h |  4 ++++
 arch/arm64/kernel/debug-monitors.c      | 26 +++++++++++++++++++++++
 arch/arm64/kernel/probes/kprobes.c      | 28 ++-----------------------
 3 files changed, 32 insertions(+), 26 deletions(-)

diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h
index 7619f473155f..b62469f3475b 100644
--- a/arch/arm64/include/asm/debug-monitors.h
+++ b/arch/arm64/include/asm/debug-monitors.h
@@ -113,6 +113,10 @@ void user_fastforward_single_step(struct task_struct *task);
 void kernel_enable_single_step(struct pt_regs *regs);
 void kernel_disable_single_step(void);
 int kernel_active_single_step(void);
+void kernel_prepare_single_step(unsigned long *flags,
+						struct pt_regs *regs);
+void kernel_cleanup_single_step(unsigned long flags,
+						struct pt_regs *regs);
 
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
 int reinstall_suspended_bps(struct pt_regs *regs);
diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index 48222a4760c2..25ce6b5a52d2 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -429,6 +429,32 @@ int kernel_active_single_step(void)
 }
 NOKPROBE_SYMBOL(kernel_active_single_step);
 
+/*
+ * Interrupts need to be disabled before single-step mode is set, and not
+ * reenabled until after single-step mode ends.
+ * Without disabling interrupt on local CPU, there is a chance of
+ * interrupt occurrence in the period of exception return and  start of
+ * out-of-line single-step, that result in wrongly single stepping
+ * into the interrupt handler.
+ */
+void kernel_prepare_single_step(unsigned long *flags,
+						struct pt_regs *regs)
+{
+	*flags = regs->pstate & DAIF_MASK;
+	regs->pstate |= PSR_I_BIT;
+	/* Unmask PSTATE.D for enabling software step exceptions. */
+	regs->pstate &= ~PSR_D_BIT;
+}
+NOKPROBE_SYMBOL(kernel_prepare_single_step);
+
+void kernel_cleanup_single_step(unsigned long flags,
+						struct pt_regs *regs)
+{
+	regs->pstate &= ~DAIF_MASK;
+	regs->pstate |= flags;
+}
+NOKPROBE_SYMBOL(kernel_cleanup_single_step);
+
 /* ptrace API */
 void user_enable_single_step(struct task_struct *task)
 {
diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index d1c95dcf1d78..c655b6b543e3 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -168,30 +168,6 @@ static void __kprobes set_current_kprobe(struct kprobe *p)
 	__this_cpu_write(current_kprobe, p);
 }
 
-/*
- * Interrupts need to be disabled before single-step mode is set, and not
- * reenabled until after single-step mode ends.
- * Without disabling interrupt on local CPU, there is a chance of
- * interrupt occurrence in the period of exception return and  start of
- * out-of-line single-step, that result in wrongly single stepping
- * into the interrupt handler.
- */
-static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
-						struct pt_regs *regs)
-{
-	kcb->saved_irqflag = regs->pstate & DAIF_MASK;
-	regs->pstate |= PSR_I_BIT;
-	/* Unmask PSTATE.D for enabling software step exceptions. */
-	regs->pstate &= ~PSR_D_BIT;
-}
-
-static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
-						struct pt_regs *regs)
-{
-	regs->pstate &= ~DAIF_MASK;
-	regs->pstate |= kcb->saved_irqflag;
-}
-
 static void __kprobes
 set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
 {
@@ -227,7 +203,7 @@ static void __kprobes setup_singlestep(struct kprobe *p,
 		set_ss_context(kcb, slot);	/* mark pending ss */
 
 		/* IRQs and single stepping do not mix well. */
-		kprobes_save_local_irqflag(kcb, regs);
+		kernel_prepare_single_step(&kcb->saved_irqflag, regs);
 		kernel_enable_single_step(regs);
 		instruction_pointer_set(regs, slot);
 	} else {
@@ -414,7 +390,7 @@ kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
 	retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
 
 	if (retval == DBG_HOOK_HANDLED) {
-		kprobes_restore_local_irqflag(kcb, regs);
+		kernel_cleanup_single_step(kcb->saved_irqflag, regs);
 		kernel_disable_single_step();
 
 		post_kprobe_handler(kcb, regs);
-- 
2.17.1