linux-kernel - [PATCH] ARC: stack unwinding: avoid indefinite looping

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Date:   Tue, 27 Oct 2020 15:32:33 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     linux-snps-arc@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, Alexey.Brodkin@...opsys.com,
        Eugeniy.Paltsev@...opsys.com, Igor.Guryanov@...opsys.com,
        Vineet Gupta <Vineet.Gupta1@...opsys.com>
Subject: [PATCH] ARC: stack unwinding: avoid indefinite looping

Currently stack unwinder is a while(1) loop which relies on the dwarf
unwinder to signal termination, which in turn relies on dwarf info to do
so. This in theory could cause an infinite loop if the dwarf info was
somehow messed up or the register contents were etc.

This fix thus detects the excessive looping and breaks the loop.

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
---
 arch/arc/kernel/stacktrace.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arc/kernel/stacktrace.c b/arch/arc/kernel/stacktrace.c
index bf40e06f3fb8..0fed32b95923 100644
--- a/arch/arc/kernel/stacktrace.c
+++ b/arch/arc/kernel/stacktrace.c
@@ -115,7 +115,7 @@ arc_unwind_core(struct task_struct *tsk, struct pt_regs *regs,
 		int (*consumer_fn) (unsigned int, void *), void *arg)
 {
 #ifdef CONFIG_ARC_DW2_UNWIND
-	int ret = 0;
+	int ret = 0, cnt = 0;
 	unsigned int address;
 	struct unwind_frame_info frame_info;
 
@@ -135,6 +135,11 @@ arc_unwind_core(struct task_struct *tsk, struct pt_regs *regs,
 			break;
 
 		frame_info.regs.r63 = frame_info.regs.r31;
+
+		if (cnt++ > 128) {
+			printk("unwinder looping too long, aborting !\n");
+			return 0;
+		}
 	}
 
 	return address;		/* return the last address it saw */
-- 
2.25.1