[PATCH v4 6/6] ubsan: Include bug type in report header

[Kees Cook <keescook@chromium.org>]

When syzbot tries to figure out how to deduplicate bug reports, it
prefers seeing a hint about a specific bug type (we can do better than
just "UBSAN"). This lifts the handler reason into the UBSAN report line
that includes the file path that tripped a check. Unfortunately, UBSAN
does not provide function names.

Suggested-by: Dmitry Vyukov <dvyukov@google.com>
Link: https://lore.kernel.org/lkml/CACT4Y+bsLJ-wFx_TaXqax3JByUOWB3uk787LsyMVcfW6JzzGvg@mail.gmail.com
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 lib/ubsan.c | 36 +++++++++++++++---------------------
 1 file changed, 15 insertions(+), 21 deletions(-)

diff --git a/lib/ubsan.c b/lib/ubsan.c
index 429663eef6a7..057d5375bfc6 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -45,13 +45,6 @@ static bool was_reported(struct source_location *location)
 	return test_and_set_bit(REPORTED_BIT, &location->reported);
 }
 
-static void print_source_location(const char *prefix,
-				struct source_location *loc)
-{
-	pr_err("%s %s:%d:%d\n", prefix, loc->file_name,
-		loc->line & LINE_MASK, loc->column & COLUMN_MASK);
-}
-
 static bool suppress_report(struct source_location *loc)
 {
 	return current->in_ubsan || was_reported(loc);
@@ -140,13 +133,14 @@ static void val_to_string(char *str, size_t size, struct type_descriptor *type,
 	}
 }
 
-static void ubsan_prologue(struct source_location *location)
+static void ubsan_prologue(struct source_location *loc, const char *reason)
 {
 	current->in_ubsan++;
 
 	pr_err("========================================"
 		"========================================\n");
-	print_source_location("UBSAN: Undefined behaviour in", location);
+	pr_err("UBSAN: %s in %s:%d:%d\n", reason, loc->file_name,
+		loc->line & LINE_MASK, loc->column & COLUMN_MASK);
 }
 
 static void ubsan_epilogue(void)
@@ -180,12 +174,12 @@ static void handle_overflow(struct overflow_data *data, void *lhs,
 	if (suppress_report(&data->location))
 		return;
 
-	ubsan_prologue(&data->location);
+	ubsan_prologue(&data->location, type_is_signed(type) ?
+			"signed integer overflow" :
+			"unsigned integer overflow");
 
 	val_to_string(lhs_val_str, sizeof(lhs_val_str), type, lhs);
 	val_to_string(rhs_val_str, sizeof(rhs_val_str), type, rhs);
-	pr_err("%s integer overflow:\n",
-		type_is_signed(type) ? "signed" : "unsigned");
 	pr_err("%s %c %s cannot be represented in type %s\n",
 		lhs_val_str,
 		op,
@@ -225,7 +219,7 @@ void __ubsan_handle_negate_overflow(struct overflow_data *data,
 	if (suppress_report(&data->location))
 		return;
 
-	ubsan_prologue(&data->location);
+	ubsan_prologue(&data->location, "negation overflow");
 
 	val_to_string(old_val_str, sizeof(old_val_str), data->type, old_val);
 
@@ -245,7 +239,7 @@ void __ubsan_handle_divrem_overflow(struct overflow_data *data,
 	if (suppress_report(&data->location))
 		return;
 
-	ubsan_prologue(&data->location);
+	ubsan_prologue(&data->location, "division overflow");
 
 	val_to_string(rhs_val_str, sizeof(rhs_val_str), data->type, rhs);
 
@@ -264,7 +258,7 @@ static void handle_null_ptr_deref(struct type_mismatch_data_common *data)
 	if (suppress_report(data->location))
 		return;
 
-	ubsan_prologue(data->location);
+	ubsan_prologue(data->location, "NULL pointer dereference");
 
 	pr_err("%s null pointer of type %s\n",
 		type_check_kinds[data->type_check_kind],
@@ -279,7 +273,7 @@ static void handle_misaligned_access(struct type_mismatch_data_common *data,
 	if (suppress_report(data->location))
 		return;
 
-	ubsan_prologue(data->location);
+	ubsan_prologue(data->location, "misaligned access");
 
 	pr_err("%s misaligned address %p for type %s\n",
 		type_check_kinds[data->type_check_kind],
@@ -295,7 +289,7 @@ static void handle_object_size_mismatch(struct type_mismatch_data_common *data,
 	if (suppress_report(data->location))
 		return;
 
-	ubsan_prologue(data->location);
+	ubsan_prologue(data->location, "object size mismatch");
 	pr_err("%s address %p with insufficient space\n",
 		type_check_kinds[data->type_check_kind],
 		(void *) ptr);
@@ -354,7 +348,7 @@ void __ubsan_handle_out_of_bounds(struct out_of_bounds_data *data, void *index)
 	if (suppress_report(&data->location))
 		return;
 
-	ubsan_prologue(&data->location);
+	ubsan_prologue(&data->location, "array index out of bounds");
 
 	val_to_string(index_str, sizeof(index_str), data->index_type, index);
 	pr_err("index %s is out of range for type %s\n", index_str,
@@ -375,7 +369,7 @@ void __ubsan_handle_shift_out_of_bounds(struct shift_out_of_bounds_data *data,
 	if (suppress_report(&data->location))
 		goto out;
 
-	ubsan_prologue(&data->location);
+	ubsan_prologue(&data->location, "shift out of bounds");
 
 	val_to_string(rhs_str, sizeof(rhs_str), rhs_type, rhs);
 	val_to_string(lhs_str, sizeof(lhs_str), lhs_type, lhs);
@@ -407,7 +401,7 @@ EXPORT_SYMBOL(__ubsan_handle_shift_out_of_bounds);
 
 void __ubsan_handle_builtin_unreachable(struct unreachable_data *data)
 {
-	ubsan_prologue(&data->location);
+	ubsan_prologue(&data->location, "unreachable");
 	pr_err("calling __builtin_unreachable()\n");
 	ubsan_epilogue();
 	panic("can't return from __builtin_unreachable()");
@@ -422,7 +416,7 @@ void __ubsan_handle_load_invalid_value(struct invalid_value_data *data,
 	if (suppress_report(&data->location))
 		return;
 
-	ubsan_prologue(&data->location);
+	ubsan_prologue(&data->location, "invalid load");
 
 	val_to_string(val_str, sizeof(val_str), data->type, val);
 
-- 
2.20.1