[RFC PATCH v2 4/4] Revert "arm64: kprobes: Allow reentering kprobes while single-stepping"

From: Hongyan Xia <[email protected]>

With the debug exception path noinstr from the vectors down to the
kprobe handlers, any Kprobe reentry under KPROBE_HIT_SS must be
considered a bug now. The special case is no longer needed.

This reverts commit 23f851ac0078a908bf3422d6467ebc1db5828c46.

Signed-off-by: Hongyan Xia <[email protected]>
---
 arch/arm64/include/asm/kprobes.h   |  6 ------
 arch/arm64/kernel/probes/kprobes.c | 23 +----------------------
 2 files changed, 1 insertion(+), 28 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 5ec5f4ef9985..ae5147a0de38 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -174,27 +174,12 @@ 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)
 {
 	__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)
@@ -255,16 +240,10 @@ 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.
-		 */
 		kprobes_inc_nmissed_count(p);
 		setup_singlestep(p, regs, kcb, 1);
 		break;
+	case KPROBE_HIT_SS:
 	case KPROBE_REENTER:
 		pr_warn("Failed to recover from reentered kprobes.\n");
 		dump_kprobe(p);
-- 
2.47.3