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

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Date:   Sun,  4 Mar 2018 23:01:32 +0530
From:   Vaibhav Jain <vaibhav@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Balbir Singh <bsingharora@...il.com>
Cc:     Vaibhav Jain <vaibhav@...ux.vnet.ibm.com>,
        Frederic Barrat <fbarrat@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Douglas Miller <dougmill@...ux.vnet.ibm.com>
Subject: [PATCH] xmon: Clear all breakpoints when xmon is disabled via debugfs

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@...ux.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