hw-breakpoints: reset bits in dr6 after the corresponding exception is handled

This patch resets the bit in dr6 after the corresponding exception is
handled in code, so that we keep a clean track of the current virtual debug
status register.

[ Impact: keep track of breakpoints triggering completion ]

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

5 files changed, 34 insertions, 6 deletions

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 4867c9f3b5fb..69451473dbd2 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -314,8 +314,12 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
 {
         int i, cpu, rc = NOTIFY_STOP;
         struct hw_breakpoint *bp;
-        /* The DR6 value is stored in args->err */
-        unsigned long dr7, dr6 = args->err;
+        unsigned long dr7, dr6;
+        unsigned long *dr6_p;
+
+        /* The DR6 value is pointed by args->err */
+        dr6_p = (unsigned long *)ERR_PTR(args->err);
+        dr6 = *dr6_p;
 
         /* Do an early return if no trap bits are set in DR6 */
         if ((dr6 & DR_TRAP_BITS) == 0)
@@ -352,6 +356,11 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
                                 rc = NOTIFY_DONE;
                 }
                 /*
+                 * Reset the 'i'th TRAP bit in dr6 to denote completion of
+                 * exception handling
+                 */
+                (*dr6_p) &= ~(DR_TRAP0 << i);
+                /*
                  * bp can be NULL due to lazy debug register switching
                  * or due to the delay between updates of hbp_kernel_pos
                  * and this_hbp_kernel.
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index b1f4dffb919e..f820b73c7f28 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -43,6 +43,7 @@
 #include <linux/smp.h>
 #include <linux/nmi.h>
 
+#include <asm/debugreg.h>
 #include <asm/apicdef.h>
 #include <asm/system.h>
 
@@ -434,6 +435,11 @@ single_step_cont(struct pt_regs *regs, struct die_args *args)
                         "resuming...\n");
         kgdb_arch_handle_exception(args->trapnr, args->signr,
                                    args->err, "c", "", regs);
+        /*
+         * Reset the BS bit in dr6 (pointed by args->err) to
+         * denote completion of processing
+         */
+        (*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;
 
         return NOTIFY_STOP;
 }
diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 7b5169d2b000..b5b1848c5336 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -54,6 +54,7 @@
 #include <asm/pgtable.h>
 #include <asm/uaccess.h>
 #include <asm/alternative.h>
+#include <asm/debugreg.h>
 
 void jprobe_return_end(void);
 
@@ -967,8 +968,14 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                         ret = NOTIFY_STOP;
                 break;
         case DIE_DEBUG:
-                if (post_kprobe_handler(args->regs))
+                if (post_kprobe_handler(args->regs)) {
+                        /*
+                         * Reset the BS bit in dr6 (pointed by args->err) to
+                         * denote completion of processing
+                         */
+                        (*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;
                         ret = NOTIFY_STOP;
+                }
                 break;
         case DIE_GPF:
                 /*
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index de9913247dd0..124a4d5a95b2 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -545,8 +545,8 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
         /* Store the virtualized DR6 value */
         tsk->thread.debugreg6 = dr6;
 
-        if (notify_die(DIE_DEBUG, "debug", regs, dr6, error_code,
-                                                SIGTRAP) == NOTIFY_STOP)
+        if (notify_die(DIE_DEBUG, "debug", regs, PTR_ERR(&dr6), error_code,
+                                                        SIGTRAP) == NOTIFY_STOP)
                 return;
 
         /* It's safe to allow irq's after DR6 has been saved */
diff --git a/arch/x86/mm/kmmio.c b/arch/x86/mm/kmmio.c
index 16ccbd77917f..11a4ad4d6253 100644
--- a/arch/x86/mm/kmmio.c
+++ b/arch/x86/mm/kmmio.c
@@ -540,8 +540,14 @@ kmmio_die_notifier(struct notifier_block *nb, unsigned long val, void *args)
         struct die_args *arg = args;
 
         if (val == DIE_DEBUG && (arg->err & DR_STEP))
-                if (post_kmmio_handler(arg->err, arg->regs) == 1)
+                if (post_kmmio_handler(arg->err, arg->regs) == 1) {
+                        /*
+                         * Reset the BS bit in dr6 (pointed by args->err) to
+                         * denote completion of processing
+                         */
+                        (*(unsigned long *)ERR_PTR(arg->err)) &= ~DR_STEP;
                         return NOTIFY_STOP;
+                }
 
         return NOTIFY_DONE;
 }