From 1c856e158fd34ef2c4475a81c1dc386329989938 Mon Sep 17 00:00:00 2001 From: Tiezhu Yang Date: Fri, 22 May 2026 15:05:07 +0800 Subject: [PATCH] LoongArch: kprobes: Fix handling of fatal unrecoverable recursions KPROBE_HIT_SS and KPROBE_REENTER are two types of fatal recursions that can not be safely recovered in kprobes. KPROBE_HIT_SS means that a kprobe is hit during single-stepping. At this point, the architecture-specific single-step context is already active. Nested single-stepping would corrupt the state, as the kprobe control block (kcb) and hardware registers cannot safely store multiple levels of stepping state. KPROBE_REENTER means that a third-level recursion occurs when a probe is hit while the system is already handling a nested probe (second- level). The kcb only provides a single slot (prev_kprobe) to backup the state. When a third probe is hit, there is no more space to save the state without corrupting the first-level backup. Kprobes work by replacing instructions with breakpoints. In order to execute the original instruction and continue, it must be moved to a temporary "single-step" slot. Since there is no backup space left to set up this slot safely, the CPU would be forced to return to the same original breakpoint address, triggering an endless loop. Currently, the code only prints a warning and returns. This leads to an infinite re-entry loop as the CPU repeatedly hits the same trap and a "stuck" CPU core because preemption was disabled at the start of the handler and never re-enabled in this early return path. Fix the logic by: 1. Merging KPROBE_HIT_SS and KPROBE_REENTER cases, as both represent fatal recursions that cannot be safely recovered. 2. Replacing WARN_ON_ONCE() with BUG() to terminate the system. This aligns LoongArch with other architectures (x86, arm64, riscv) and prevents stack overflow while providing diagnostic information. Fixes: 6d4cc40fb5f5 ("LoongArch: Add kprobes support") Signed-off-by: Tiezhu Yang Signed-off-by: Huacai Chen --- arch/loongarch/kernel/kprobes.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/loongarch/kernel/kprobes.c b/arch/loongarch/kernel/kprobes.c index 04b5b05715cd..1985ed30dd16 100644 --- a/arch/loongarch/kernel/kprobes.c +++ b/arch/loongarch/kernel/kprobes.c @@ -186,16 +186,16 @@ static bool reenter_kprobe(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb) { switch (kcb->kprobe_status) { - case KPROBE_HIT_SS: case KPROBE_HIT_SSDONE: case KPROBE_HIT_ACTIVE: 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); - WARN_ON_ONCE(1); + BUG(); break; default: WARN_ON(1);