tracing/probes: Reject symbol/symstr type for uprobe

Since uprobe's argument must contain the user-space data, that
should not be converted to kernel symbols. Reject if user
specifies these types on uprobe events. e.g.

 /sys/kernel/debug/tracing # echo 'p /bin/sh:10 %ax:symbol' >> uprobe_events
 sh: write error: Invalid argument
 /sys/kernel/debug/tracing # echo 'p /bin/sh:10 %ax:symstr' >> uprobe_events
 sh: write error: Invalid argument
 /sys/kernel/debug/tracing # cat error_log
 [ 1783.134883] trace_uprobe: error: Unknown type is specified
   Command: p /bin/sh:10 %ax:symbol
                             ^
 [ 1792.201120] trace_uprobe: error: Unknown type is specified
   Command: p /bin/sh:10 %ax:symstr
                             ^
Link: https://lore.kernel.org/all/166679931679.1528100.15540755370726009882.stgit@devnote3/Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

kernel/trace/trace_probe.c

@@ -100,10 +100,15 @@ static const struct fetch_type probe_fetch_types[] = {
 	ASSIGN_FETCH_TYPE_END
 };
 
-static const struct fetch_type *find_fetch_type(const char *type)
+static const struct fetch_type *find_fetch_type(const char *type, unsigned long flags)
 {
 	int i;
 
+	/* Reject the symbol/symstr for uprobes */
+	if (type && (flags & TPARG_FL_USER) &&
+	    (!strcmp(type, "symbol") || !strcmp(type, "symstr")))
+		return NULL;
+
 	if (!type)
 		type = DEFAULT_FETCH_TYPE_STR;
 
@@ -121,13 +126,13 @@ static const struct fetch_type *find_fetch_type(const char *type)
 
 		switch (bs) {
 		case 8:
-			return find_fetch_type("u8");
+			return find_fetch_type("u8", flags);
 		case 16:
-			return find_fetch_type("u16");
+			return find_fetch_type("u16", flags);
 		case 32:
-			return find_fetch_type("u32");
+			return find_fetch_type("u32", flags);
 		case 64:
-			return find_fetch_type("u64");
+			return find_fetch_type("u64", flags);
 		default:
 			goto fail;
 		}
@@ -480,7 +485,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 					    DEREF_OPEN_BRACE);
 			return -EINVAL;
 		} else {
-			const struct fetch_type *t2 = find_fetch_type(NULL);
+			const struct fetch_type *t2 = find_fetch_type(NULL, flags);
 
 			*tmp = '\0';
 			ret = parse_probe_arg(arg, t2, &code, end, flags, offs);
@@ -632,9 +637,9 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 		/* The type of $comm must be "string", and not an array. */
 		if (parg->count || (t && strcmp(t, "string")))
 			goto out;
-		parg->type = find_fetch_type("string");
+		parg->type = find_fetch_type("string", flags);
 	} else
-		parg->type = find_fetch_type(t);
+		parg->type = find_fetch_type(t, flags);
 	if (!parg->type) {
 		trace_probe_log_err(offset + (t ? (t - arg) : 0), BAD_TYPE);
 		goto out;

kernel/trace/trace_probe.h

@@ -358,7 +358,8 @@ int trace_probe_create(const char *raw_command, int (*createfn)(int, const char
 #define TPARG_FL_KERNEL BIT(1)
 #define TPARG_FL_FENTRY BIT(2)
 #define TPARG_FL_TPOINT BIT(3)
-#define TPARG_FL_MASK	GENMASK(3, 0)
+#define TPARG_FL_USER   BIT(4)
+#define TPARG_FL_MASK	GENMASK(4, 0)
 
 extern int traceprobe_parse_probe_arg(struct trace_probe *tp, int i,
 				const char *argv, unsigned int flags);

kernel/trace/trace_uprobe.c

@@ -691,7 +691,8 @@ static int __trace_uprobe_create(int argc, const char **argv)
 	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
 		trace_probe_log_set_index(i + 2);
 		ret = traceprobe_parse_probe_arg(&tu->tp, i, argv[i],
-					is_return ? TPARG_FL_RETURN : 0);
+					(is_return ? TPARG_FL_RETURN : 0) |
+					TPARG_FL_USER);
 		if (ret)
 			goto error;
 	}

tools/testing/selftests/ftrace/test.d/kprobe/uprobe_syntax_errors.tc

@@ -23,4 +23,9 @@ check_error 'p /bin/sh:10^%hoge'	# BAD_ADDR_SUFFIX
 check_error 'p /bin/sh:10(10)^%return'	# BAD_REFCNT_SUFFIX
 fi
 
+# symstr is not supported by uprobe
+if grep -q ".*symstr.*" README; then
+check_error 'p /bin/sh:10 $stack0:^symstr'	# BAD_TYPE
+fi
+
 exit 0