2 files changed, 66 insertions, 24 deletions

diff --git a/Documentation/trace/events.rst b/Documentation/trace/events.rst
index 45e66a60a816..c47f381d0c00 100644
--- a/Documentation/trace/events.rst
+++ b/Documentation/trace/events.rst
@@ -198,6 +198,15 @@ The glob (~) accepts a wild card character (\*,?) and character classes
   prev_comm ~ "*sh*"
   prev_comm ~ "ba*sh"
 
+If the field is a pointer that points into user space (for example
+"filename" from sys_enter_openat), then you have to append ".ustring" to the
+field name::
+
+  filename.ustring ~ "password"
+
+As the kernel will have to know how to retrieve the memory that the pointer
+is at from user space.
+
 5.2 Setting filters
 -------------------
 
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 2e9ef64e9ee9..b458a9afa2c0 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -667,6 +667,23 @@ static __percpu struct ustring_buffer *ustring_per_cpu;
 static __always_inline char *test_string(char *str)
 {
 	struct ustring_buffer *ubuf;
+	char *kstr;
+
+	if (!ustring_per_cpu)
+		return NULL;
+
+	ubuf = this_cpu_ptr(ustring_per_cpu);
+	kstr = ubuf->buffer;
+
+	/* For safety, do not trust the string pointer */
+	if (!strncpy_from_kernel_nofault(kstr, str, USTRING_BUF_SIZE))
+		return NULL;
+	return kstr;
+}
+
+static __always_inline char *test_ustring(char *str)
+{
+	struct ustring_buffer *ubuf;
 	char __user *ustr;
 	char *kstr;
 
@@ -676,23 +693,11 @@ static __always_inline char *test_string(char *str)
 	ubuf = this_cpu_ptr(ustring_per_cpu);
 	kstr = ubuf->buffer;
 
-	/*
-	 * We use TASK_SIZE to denote user or kernel space, but this will
-	 * not work for all architectures. If it picks the wrong one, it may
-	 * just fail the filter (but will not bug).
-	 *
-	 * TODO: Have a way to properly denote which one this is for.
-	 */
-	if (likely((unsigned long)str >= TASK_SIZE)) {
-		/* For safety, do not trust the string pointer */
-		if (!strncpy_from_kernel_nofault(kstr, str, USTRING_BUF_SIZE))
-			return NULL;
-	} else {
-		/* user space address? */
-		ustr = (char __user *)str;
-		if (!strncpy_from_user_nofault(kstr, ustr, USTRING_BUF_SIZE))
-			return NULL;
-	}
+	/* user space address? */
+	ustr = (char __user *)str;
+	if (!strncpy_from_user_nofault(kstr, ustr, USTRING_BUF_SIZE))
+		return NULL;
+
 	return kstr;
 }
 
@@ -709,24 +714,42 @@ static int filter_pred_string(struct filter_pred *pred, void *event)
 	return match;
 }
 
+static __always_inline int filter_pchar(struct filter_pred *pred, char *str)
+{
+	int cmp, match;
+	int len;
+
+	len = strlen(str) + 1;	/* including tailing '\0' */
+	cmp = pred->regex.match(str, &pred->regex, len);
+
+	match = cmp ^ pred->not;
+
+	return match;
+}
 /* Filter predicate for char * pointers */
 static int filter_pred_pchar(struct filter_pred *pred, void *event)
 {
 	char **addr = (char **)(event + pred->offset);
 	char *str;
-	int cmp, match;
-	int len;
 
 	str = test_string(*addr);
 	if (!str)
 		return 0;
 
-	len = strlen(str) + 1;	/* including tailing '\0' */
-	cmp = pred->regex.match(str, &pred->regex, len);
+	return filter_pchar(pred, str);
+}
 
-	match = cmp ^ pred->not;
+/* Filter predicate for char * pointers in user space*/
+static int filter_pred_pchar_user(struct filter_pred *pred, void *event)
+{
+	char **addr = (char **)(event + pred->offset);
+	char *str;
 
-	return match;
+	str = test_ustring(*addr);
+	if (!str)
+		return 0;
+
+	return filter_pchar(pred, str);
 }
 
 /*
@@ -1232,6 +1255,7 @@ static int parse_pred(const char *str, void *data,
 	struct filter_pred *pred = NULL;
 	char num_buf[24];	/* Big enough to hold an address */
 	char *field_name;
+	bool ustring = false;
 	char q;
 	u64 val;
 	int len;
@@ -1266,6 +1290,12 @@ static int parse_pred(const char *str, void *data,
 		return -EINVAL;
 	}
 
+	/* See if the field is a user space string */
+	if ((len = str_has_prefix(str + i, ".ustring"))) {
+		ustring = true;
+		i += len;
+	}
+
 	while (isspace(str[i]))
 		i++;
 
@@ -1405,7 +1435,10 @@ static int parse_pred(const char *str, void *data,
 					goto err_mem;
 			}
 
-			pred->fn = filter_pred_pchar;
+			if (ustring)
+				pred->fn = filter_pred_pchar_user;
+			else
+				pred->fn = filter_pred_pchar;
 		}
 		/* go past the last quote */
 		i++;