[RFC PATCH 7/9] arm64/kprobes: Drop the KPROBE_HIT_SS reentry special case

[Hongyan Xia]

From: Hongyan Xia <hongyan.xia@xxxxxxxxxxxxx>

With the debug exception path noinstr from the vectors down to the
kprobe handlers and the only instrumentable code in the flow confined to
instrumentation_begin()/end() windows, a kprobe hit while another probe
is in KPROBE_HIT_SS can no longer happen.

Signed-off-by: Hongyan Xia <hongyan.xia@xxxxxxxxxxxxx>
---
 arch/arm64/include/asm/kprobes.h   |  6 ------
 arch/arm64/kernel/probes/kprobes.c | 21 +--------------------
 2 files changed, 1 insertion(+), 26 deletions(-)

diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index a694f7d34f45..bff8ba9c1689 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -26,12 +26,6 @@
 struct prev_kprobe {
 	struct kprobe *kp;
 	unsigned int status;
-
-	/*
-	 * The original DAIF state of the outer kprobe, saved here before
-	 * a nested kprobe overwrites kcb->saved_irqflag during reentry.
-	 */
-	unsigned long saved_irqflag;
 };
 
 /* per-cpu kprobe control block */
diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 4172998d48d9..1658b6acd803 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -176,13 +176,6 @@ static void noinstr save_previous_kprobe(struct kprobe_ctlblk *kcb)
 	kcb->prev_kprobe.kp = kprobe_running();
 	kcb->prev_kprobe.status = kcb->kprobe_status;
 
-	/*
-	 * Save the outer kprobe's original DAIF flags before the nested
-	 * kprobe calls kprobes_save_local_irqflag() and overwrites
-	 * kcb->saved_irqflag. Without this, the outer kprobe will restore
-	 * the wrong DAIF state and leave interrupts permanently masked.
-	 */
-	kcb->prev_kprobe.saved_irqflag = kcb->saved_irqflag;
 }
 
 static void noinstr restore_previous_kprobe(struct kprobe_ctlblk *kcb)
@@ -190,12 +183,6 @@ static void noinstr restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 	kcb->kprobe_status = kcb->prev_kprobe.status;
 
-	/*
-	 * Restore the outer kprobe's saved_irqflag so that when its
-	 * single-step completes, kprobes_restore_local_irqflag() uses
-	 * the correct original DAIF value.
-	 */
-	kcb->saved_irqflag = kcb->prev_kprobe.saved_irqflag;
 }
 
 static void noinstr set_current_kprobe(struct kprobe *p)
@@ -258,18 +245,12 @@ static int noinstr reenter_kprobe(struct kprobe *p,
 	switch (kcb->kprobe_status) {
 	case KPROBE_HIT_SSDONE:
 	case KPROBE_HIT_ACTIVE:
-	case KPROBE_HIT_SS:
-		/*
-		 * A probe can be hit while another kprobe is preparing or
-		 * executing its XOL single-step instruction. This is still a
-		 * recoverable one-level reentry, so handle it in the same way as
-		 * reentry from KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE.
-		 */
 		instrumentation_begin();
 		kprobes_inc_nmissed_count(p);
 		instrumentation_end();
 		setup_singlestep(p, regs, kcb, 1);
 		break;
+	case KPROBE_HIT_SS:
 	case KPROBE_REENTER:
 		instrumentation_begin();
 		pr_warn("Failed to recover from reentered kprobes.\n");
-- 
2.47.3