[PATCH v2 1/2] arm64: kprobes: disable preemption across XOL single-step

[Khaja Hussain Shaik Khaji]

On arm64, non-emulatable kprobes instructions execute out-of-line (XOL)
after returning from the initial debug exception. The XOL instruction
runs in normal kernel context, while kprobe state is maintained per-CPU.

If the task is preempted or migrates during the XOL window, the subsequent
SS-BRK exception may be handled on a different CPU, corrupting per-CPU
kprobe state and preventing correct recovery.

Disable preemption across the XOL instruction and re-enable it in the
SS-BRK handler to prevent migration until control returns to the kprobe
handler.

Signed-off-by: Khaja Hussain Shaik Khaji <khaja.khaji at oss.qualcomm.com>
---
 arch/arm64/kernel/probes/kprobes.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 43a0361a8bf0..d8a70c456543 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -227,6 +227,14 @@ static void __kprobes setup_singlestep(struct kprobe *p,
 
 		kprobes_save_local_irqflag(kcb, regs);
 		instruction_pointer_set(regs, slot);
+
+		/*
+		 * Disable preemption across the out-of-line (XOL) instruction.
+		 * The XOL instruction executes in normal kernel context and
+		 * kprobe state is per-CPU.
+		 */
+		preempt_disable();
+
 	} else {
 		/* insn simulation */
 		arch_simulate_insn(p, regs);
@@ -363,6 +371,11 @@ kprobe_ss_brk_handler(struct pt_regs *regs, unsigned long esr)
 		kprobes_restore_local_irqflag(kcb, regs);
 		post_kprobe_handler(cur, kcb, regs);
 
+		/*
+		 * Re-enable preemption after completing the XOL instruction.
+		 */
+		preempt_enable_no_resched();
+
 		return DBG_HOOK_HANDLED;
 	}
 
-- 
2.34.1