x86, ptrace: add buffer size checks

Pass the buffer size for (most) ptrace commands that pass user-allocated buffers and check that size before accessing the buffer. Unfortunately, PTRACE_BTS_GET already uses all 4 parameters.
Commands that access user buffers return the number of bytes or records read or written.
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/ptrace.c

@@ -591,6 +591,7 @@ static int ptrace_bts_clear(struct task_struct *child)
 }
 
 static int ptrace_bts_drain(struct task_struct *child,
+			    long size,
 			    struct bts_struct __user *out)
 {
 	int end, i;
@@ -603,6 +604,9 @@ static int ptrace_bts_drain(struct task_struct *child,
 	if (end <= 0)
 		return end;
 
+	if (size < (end * sizeof(struct bts_struct)))
+		return -EIO;
+
 	for (i = 0; i < end; i++, out++) {
 		struct bts_struct ret;
 		int retval;
@@ -617,7 +621,7 @@ static int ptrace_bts_drain(struct task_struct *child,
 
 	ds_clear(ds);
 
-	return i;
+	return end;
 }
 
 static int ptrace_bts_realloc(struct task_struct *child,
@@ -690,15 +694,22 @@ out:
 }
 
 static int ptrace_bts_config(struct task_struct *child,
+			     long cfg_size,
 			     const struct ptrace_bts_config __user *ucfg)
 {
 	struct ptrace_bts_config cfg;
 	int bts_size, ret = 0;
 	void *ds;
 
+	if (cfg_size < sizeof(cfg))
+		return -EIO;
+
 	if (copy_from_user(&cfg, ucfg, sizeof(cfg)))
 		return -EFAULT;
 
+	if ((int)cfg.size < 0)
+		return -EINVAL;
+
 	bts_size = 0;
 	ds = (void *)child->thread.ds_area_msr;
 	if (ds) {
@@ -734,6 +745,8 @@ static int ptrace_bts_config(struct task_struct *child,
 	else
 		clear_tsk_thread_flag(child, TIF_BTS_TRACE_TS);
 
+	ret = sizeof(cfg);
+
 out:
 	if (child->thread.debugctlmsr)
 		set_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
@@ -749,11 +762,15 @@ errout:
 }
 
 static int ptrace_bts_status(struct task_struct *child,
+			     long cfg_size,
 			     struct ptrace_bts_config __user *ucfg)
 {
 	void *ds = (void *)child->thread.ds_area_msr;
 	struct ptrace_bts_config cfg;
 
+	if (cfg_size < sizeof(cfg))
+		return -EIO;
+
 	memset(&cfg, 0, sizeof(cfg));
 
 	if (ds) {
@@ -923,12 +940,12 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 
 	case PTRACE_BTS_CONFIG:
 		ret = ptrace_bts_config
-			(child, (struct ptrace_bts_config __user *)addr);
+			(child, data, (struct ptrace_bts_config __user *)addr);
 		break;
 
 	case PTRACE_BTS_STATUS:
 		ret = ptrace_bts_status
-			(child, (struct ptrace_bts_config __user *)addr);
+			(child, data, (struct ptrace_bts_config __user *)addr);
 		break;
 
 	case PTRACE_BTS_SIZE:
@@ -946,7 +963,7 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 
 	case PTRACE_BTS_DRAIN:
 		ret = ptrace_bts_drain
-			(child, (struct bts_struct __user *) addr);
+			(child, data, (struct bts_struct __user *) addr);
 		break;
 
 	default:

include/asm-x86/ptrace-abi.h

@@ -99,13 +99,15 @@ struct ptrace_bts_config {
 
 #define PTRACE_BTS_CONFIG	40
 /* Configure branch trace recording.
-   DATA is ignored, ADDR points to a struct ptrace_bts_config.
+   ADDR points to a struct ptrace_bts_config.
+   DATA gives the size of that buffer.
    A new buffer is allocated, iff the size changes.
+   Returns the number of bytes read.
 */
 #define PTRACE_BTS_STATUS	41
-/* Return the current configuration.
-   DATA is ignored, ADDR points to a struct ptrace_bts_config
-   that will contain the result.
+/* Return the current configuration in a struct ptrace_bts_config
+   pointed to by ADDR; DATA gives the size of that buffer.
+   Returns the number of bytes written.
 */
 #define PTRACE_BTS_SIZE		42
 /* Return the number of available BTS records.
@@ -123,8 +125,8 @@ struct ptrace_bts_config {
 */
 #define PTRACE_BTS_DRAIN	45
 /* Read all available BTS records and clear the buffer.
-   DATA is ignored. ADDR points to an array of struct bts_struct of
-   suitable size.
+   ADDR points to an array of struct bts_struct.
+   DATA gives the size of that buffer.
    BTS records are read from oldest to newest.
    Returns number of BTS records drained.
 */