As Colin Cross noticed, serial ports could be noisy, so occasional
characters once in a while are possible. So, considering the noise
possibility, entering the debugger on any received byte is unacceptable
for production devices.
This changes KGDB FIQ behaviour in a such way so that we have to type the
GDB-protocol "$3#33" command to actually enter the debugger, the kernel
will print the following prompt:
Type $3#33 to enter the debugger.
This is the exactly the same command we use to escape from KGDB to KDB,
so it should be all pretty familiar.
For convenience, there is a kgdb_fiq.knock kernel command line option,
when set to 0, this turns the special command to just a return key
press, so the kernel will be printing this:
Hit <return> to enter the debugger.
Suggested-by: Colin Cross <[email protected]>
Signed-off-by: Anton Vorontsov <[email protected]>
---
arch/arm/kernel/kgdb_fiq.c | 48 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 48 insertions(+)
diff --git a/arch/arm/kernel/kgdb_fiq.c b/arch/arm/kernel/kgdb_fiq.c
index 7ec9979..5308697 100644
--- a/arch/arm/kernel/kgdb_fiq.c
+++ b/arch/arm/kernel/kgdb_fiq.c
@@ -17,6 +17,7 @@
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/hardirq.h>
+#include <linux/kdb.h>
#include <linux/kgdb.h>
#include <asm/fiq.h>
#include <asm/exception.h>
@@ -25,6 +26,51 @@ static int kgdb_fiq_enabled;
module_param_named(enable, kgdb_fiq_enabled, int, 0600);
MODULE_PARM_DESC(enable, "set to 1 to enable FIQ KGDB");
+static bool kgdb_fiq_knock = 1;
+module_param_named(knock, kgdb_fiq_knock, bool, 0600);
+MODULE_PARM_DESC(knock, "'$3#33' command must be used to enter the debugger");
+
+/*
+ * "Serial ports are often noisy, especially when muxed over another port (we
+ * often use serial over the headset connector). Noise on the async command
+ * line just causes characters that are ignored, on a command line that blocked
+ * execution noise would be catastrophic." -- Colin Cross
+ *
+ * So, this small function implements KGDB/KDB knocking on the serial line: we
+ * won't enter the debugger until we receive a known magic phrase (which is
+ * actually "$3#33", known as "escape to KDB" command. If knocking is disabled,
+ * just pressing the return key is enough to enter the debugger.
+ */
+static bool kgdb_fiq_poll_knock(void)
+{
+ static int n;
+ int c = -1;
+ get_char_func *getc;
+ const char *magic = "$3#33";
+ size_t m = strlen(magic);
+
+ for (getc = &kdb_poll_funcs[0]; *getc; ++getc) {
+ c = (*getc)();
+ if (c >= 0)
+ break;
+ }
+
+ if (!kgdb_fiq_knock && (c == '\r' || c == '\n')) {
+ return 1;
+ } else if (c == magic[n]) {
+ kdb_printf("%c", c);
+ n = (n + 1) % m;
+ if (!n)
+ return 1;
+ } else {
+ n = 0;
+ kdb_printf("\n%s %s to enter the debugger.\n",
+ kgdb_fiq_knock ? "Type" : "Hit",
+ kgdb_fiq_knock ? magic : "<return>");
+ }
+ return 0;
+}
+
static unsigned int kgdb_fiq;
static void (*kgdb_enable_fiq)(unsigned int irq, bool on);
static bool (*is_kgdb_fiq)(unsigned int irq);
@@ -33,6 +79,8 @@ asmlinkage void __exception_irq_entry
kgdb_fiq_do_handle(struct pt_regs *regs)
{
if (!is_kgdb_fiq(kgdb_fiq))
return;
+ if (!kgdb_fiq_poll_knock())
+ return;
nmi_enter();
kgdb_handle_exception(1, 0, 0, regs);
--
1.7.10.4
------------------------------------------------------------------------------
Live Security Virtual Conference
Exclusive live event will cover all the ways today's security and
threat landscape has changed and how IT managers can respond. Discussions
will include endpoint security, mobile security and the latest in malware
threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/
_______________________________________________
Kgdb-bugreport mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport
