[PATCH v5 3/4] perf annotate-data: Allow out-of-size access for flex-array types

[Namhyung Kim <namhyung@kernel.org>]

Structs that have a flex array will have accesses beyond its original
size as the array was declared as 0 sized.  For now, it just allow any
offset bigger than the size.  It could be refined later.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/annotate-data.c | 63 ++++++++++++++++++---------------
 tools/perf/util/annotate-data.h |  2 ++
 2 files changed, 36 insertions(+), 29 deletions(-)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index 845a5d8c2b84b6a6..5dd6c6ec2d42451d 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -7,6 +7,7 @@
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <inttypes.h>
 #include <linux/zalloc.h>
 
@@ -249,8 +250,15 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
 
 	die_get_real_type(die, &die_mem);
 
-	if (dwarf_aggregate_size(&die_mem, &size) < 0)
-		size = 0;
+	if (dwarf_aggregate_size(&die_mem, &size) < 0 || size == 0) {
+		if (dwarf_tag(&die_mem) == DW_TAG_array_type) { /* flex-array? */
+			die_get_real_type(&die_mem, &die_mem);
+			if (dwarf_aggregate_size(&die_mem, &size) < 0)
+				size = 0;
+		} else {
+			size = 0;
+		}
+	}
 
 	if (dwarf_attr_integrate(die, DW_AT_data_member_location, &attr)) {
 		if (dwarf_formudata(&attr, &loc) != 0) {
@@ -400,6 +408,7 @@ static struct annotated_data_type *dso__findnew_data_type(struct dso *dso,
 	result->self.type_name = type_name;
 	result->self.size = size;
 	INIT_LIST_HEAD(&result->self.children);
+	result->flex_array = die_has_flex_array(type_die);
 
 	if (symbol_conf.annotate_data_member)
 		add_member_types(result, type_die);
@@ -518,13 +527,30 @@ static bool is_better_type(Dwarf_Die *type_a, Dwarf_Die *type_b)
 	return false;
 }
 
+static enum type_match_result check_type_offset(Dwarf_Die *type_die, int offset)
+{
+	Dwarf_Word size;
+
+	/* Get the size of the actual type */
+	if (dwarf_aggregate_size(type_die, &size) < 0)
+		return PERF_TMR_NO_SIZE;
+
+	/* Minimal sanity check */
+	if (offset < 0)
+		return PERF_TMR_BAD_OFFSET;
+
+	if ((unsigned)offset >= size && !die_has_flex_array(type_die))
+		return PERF_TMR_BAD_OFFSET;
+
+	return PERF_TMR_OK;
+}
+
 /* The type info will be saved in @type_die */
 static enum type_match_result check_variable(struct data_loc_info *dloc,
 					     Dwarf_Die *var_die,
 					     Dwarf_Die *type_die, int reg,
 					     int offset, bool is_fbreg)
 {
-	Dwarf_Word size;
 	bool needs_pointer = true;
 	Dwarf_Die sized_type;
 
@@ -555,15 +581,7 @@ static enum type_match_result check_variable(struct data_loc_info *dloc,
 	else
 		sized_type = *type_die;
 
-	/* Get the size of the actual type */
-	if (dwarf_aggregate_size(&sized_type, &size) < 0)
-		return PERF_TMR_NO_SIZE;
-
-	/* Minimal sanity check */
-	if ((unsigned)offset >= size)
-		return PERF_TMR_BAD_OFFSET;
-
-	return PERF_TMR_OK;
+	return check_type_offset(&sized_type, offset);
 }
 
 struct type_state_stack *find_stack_state(struct type_state *state,
@@ -1113,7 +1131,6 @@ static enum type_match_result check_matching_type(struct type_state *state,
 						  struct disasm_line *dl,
 						  Dwarf_Die *type_die)
 {
-	Dwarf_Word size;
 	u32 insn_offset = dl->al.offset;
 	int reg = dloc->op->reg1;
 	int offset = dloc->op->offset;
@@ -1167,12 +1184,7 @@ static enum type_match_result check_matching_type(struct type_state *state,
 		else
 			sized_type = *type_die;
 
-		/* Get the size of the actual type */
-		if (dwarf_aggregate_size(&sized_type, &size) < 0 ||
-		    (unsigned)dloc->type_offset >= size)
-			return PERF_TMR_BAD_OFFSET;
-
-		return PERF_TMR_OK;
+		return check_type_offset(&sized_type, dloc->type_offset);
 	}
 
 	if (state->regs[reg].kind == TSR_KIND_POINTER) {
@@ -1191,12 +1203,7 @@ static enum type_match_result check_matching_type(struct type_state *state,
 
 		dloc->type_offset = dloc->op->offset + state->regs[reg].offset;
 
-		/* Get the size of the actual type */
-		if (dwarf_aggregate_size(type_die, &size) < 0 ||
-		    (unsigned)dloc->type_offset >= size)
-			return PERF_TMR_BAD_OFFSET;
-
-		return PERF_TMR_OK;
+		return check_type_offset(type_die, dloc->type_offset);
 	}
 
 	if (state->regs[reg].kind == TSR_KIND_PERCPU_POINTER) {
@@ -1210,9 +1217,7 @@ static enum type_match_result check_matching_type(struct type_state *state,
 
 		dloc->type_offset = dloc->op->offset;
 
-		/* Get the size of the actual type */
-		if (dwarf_aggregate_size(type_die, &size) < 0 ||
-		    (unsigned)dloc->type_offset >= size)
+		if (check_type_offset(type_die, dloc->type_offset) != PERF_TMR_OK)
 			return PERF_TMR_BAIL_OUT;
 
 		return PERF_TMR_OK;
@@ -1840,7 +1845,7 @@ int annotated_data_type__update_samples(struct annotated_data_type *adt,
 			return -1;
 	}
 
-	if (offset < 0 || offset >= adt->self.size)
+	if (offset < 0 || (offset >= adt->self.size && !adt->flex_array))
 		return -1;
 
 	h = &adt->histograms[evsel->core.idx];
diff --git a/tools/perf/util/annotate-data.h b/tools/perf/util/annotate-data.h
index ca2096a9ee62cbfe..957726334907cc0e 100644
--- a/tools/perf/util/annotate-data.h
+++ b/tools/perf/util/annotate-data.h
@@ -85,6 +85,7 @@ struct type_hist {
  * struct annotated_data_type - Data type to profile
  * @node: RB-tree node for dso->type_tree
  * @self: Actual type information
+ * @flex_array: Whether it has a flex array
  * @nr_histogram: Number of histogram entries
  * @histograms: An array of histograms
  *
@@ -93,6 +94,7 @@ struct type_hist {
 struct annotated_data_type {
 	struct rb_node node;
 	struct annotated_member self;
+	bool flex_array;
 	int nr_histograms;
 	struct type_hist *histograms;
 };
-- 
2.55.0