[PATCH] xmon: Clear all breakpoints when xmon is disabled via debugfs

* [PATCH] xmon: Clear all breakpoints when xmon is disabled via debugfs
@ 2018-03-04 17:31 Vaibhav Jain
  2018-03-04 21:27 ` Balbir Singh
  2018-03-14  9:28 ` Michael Ellerman
  0 siblings, 2 replies; 3+ messages in thread
From: Vaibhav Jain @ 2018-03-04 17:31 UTC (permalink / raw)
  To: Michael Ellerman, Balbir Singh
  Cc: Vaibhav Jain, Frederic Barrat, linuxppc-dev, linux-kernel,
	Benjamin Herrenschmidt, Paul Mackerras, Nicholas Piggin,
	Douglas Miller

Presently when xmon is disabled by debugfs any existing
instruction/data-access breakpoints set are not disabled. This may
lead to kernel oops when those breakpoints are hit as the necessary
debugger hooks aren't installed.

Hence this patch introduces a new function named clear_all_bpt()
which is called when xmon is disabled via debugfs. The function will
unpatch/clear all the trap and ciabr/dab based breakpoints.

Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
---
 arch/powerpc/xmon/xmon.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index e9c7ec8f15f8..f43aacd74625 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -903,6 +903,27 @@ static void remove_bpts(void)
 	}
 }
 
+static void clear_all_bpt(void)
+{
+	int i;
+
+	/* clear/unpatch all breakpoints */
+	remove_bpts();
+	remove_cpu_bpts();
+
+	/* Disable all breakpoints */
+	for (i = 0; i < NBPTS; ++i)
+		bpts[i].enabled = 0;
+
+	/* Clear any data or iabr breakpoints */
+	if (iabr || dabr.enabled) {
+		iabr = NULL;
+		dabr.enabled = 0;
+	}
+
+	printf("xmon: All breakpoints cleared\n");
+}
+
 static void remove_cpu_bpts(void)
 {
 	hw_breakpoint_disable();
@@ -3671,6 +3692,9 @@ static int xmon_dbgfs_set(void *data, u64 val)
 	xmon_on = !!val;
 	xmon_init(xmon_on);
 
+	/* make sure all breakpoints removed when disabling */
+	if (!xmon_on)
+		clear_all_bpt();
 	return 0;
 }
 
-- 
2.14.3

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