linux-kernel - [PATCH v3] tracing/cfi: Fix cmp_entries

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Date:   Wed, 13 Oct 2021 21:52:17 -0700
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     surenb@...gle.com, hridya@...gle.com, namhyung@...nel.org,
        samitolvanen@...gle.com, ndesaulniers@...gle.com,
        kernel-team@...roid.com, Kalesh Singh <kaleshsingh@...gle.com>,
        kernel test robot <lkp@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v3] tracing/cfi: Fix cmp_entries_* functions signature mismatch

If CONFIG_CFI_CLANG=y, attempting to read an event histogram will cause
the kernel to panic due to failed CFI check.

    1. echo 'hist:keys=common_pid' >> events/sched/sched_switch/trigger
    2. cat events/sched/sched_switch/hist
    3. kernel panics on attempting to read hist

This happens because the sort() function expects a generic
int (*)(const void *, const void *) pointer for the compare function.
To prevent this CFI failure, change tracing map cmp_entries_* function
signatures to match this.

Also, fix the build error reported by the kernel test robot [1].

[1] https://lore.kernel.org/r/202110141140.zzi4dRh4-lkp@intel.com/

Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
Reported-by: kernel test robot <lkp@...el.com>
---
Changes in v3:
  - Fix build error, reported by kernel test robot

Changes in v2:
  - Code style clean up, per Steve
  - Commit message typo fix, per Steve


 kernel/trace/tracing_map.c | 40 ++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 17 deletions(-)

diff --git a/kernel/trace/tracing_map.c b/kernel/trace/tracing_map.c
index d6bddb157ef2..39bb56d2dcbe 100644
--- a/kernel/trace/tracing_map.c
+++ b/kernel/trace/tracing_map.c
@@ -834,29 +834,35 @@ int tracing_map_init(struct tracing_map *map)
 	return err;
 }
 
-static int cmp_entries_dup(const struct tracing_map_sort_entry **a,
-			   const struct tracing_map_sort_entry **b)
+static int cmp_entries_dup(const void *A, const void *B)
 {
+	const struct tracing_map_sort_entry *a, *b;
 	int ret = 0;
 
-	if (memcmp((*a)->key, (*b)->key, (*a)->elt->map->key_size))
+	a = *(const struct tracing_map_sort_entry **)A;
+	b = *(const struct tracing_map_sort_entry **)B;
+
+	if (memcmp(a->key, b->key, a->elt->map->key_size))
 		ret = 1;
 
 	return ret;
 }
 
-static int cmp_entries_sum(const struct tracing_map_sort_entry **a,
-			   const struct tracing_map_sort_entry **b)
+static int cmp_entries_sum(const void *A, const void *B)
 {
 	const struct tracing_map_elt *elt_a, *elt_b;
+	const struct tracing_map_sort_entry *a, *b;
 	struct tracing_map_sort_key *sort_key;
 	struct tracing_map_field *field;
 	tracing_map_cmp_fn_t cmp_fn;
 	void *val_a, *val_b;
 	int ret = 0;
 
-	elt_a = (*a)->elt;
-	elt_b = (*b)->elt;
+	a = *(const struct tracing_map_sort_entry **)A;
+	b = *(const struct tracing_map_sort_entry **)B;
+
+	elt_a = a->elt;
+	elt_b = b->elt;
 
 	sort_key = &elt_a->map->sort_key;
 
@@ -873,18 +879,21 @@ static int cmp_entries_sum(const struct tracing_map_sort_entry **a,
 	return ret;
 }
 
-static int cmp_entries_key(const struct tracing_map_sort_entry **a,
-			   const struct tracing_map_sort_entry **b)
+static int cmp_entries_key(const void *A, const void *B)
 {
 	const struct tracing_map_elt *elt_a, *elt_b;
+	const struct tracing_map_sort_entry *a, *b;
 	struct tracing_map_sort_key *sort_key;
 	struct tracing_map_field *field;
 	tracing_map_cmp_fn_t cmp_fn;
 	void *val_a, *val_b;
 	int ret = 0;
 
-	elt_a = (*a)->elt;
-	elt_b = (*b)->elt;
+	a = *(const struct tracing_map_sort_entry **)A;
+	b = *(const struct tracing_map_sort_entry **)B;
+
+	elt_a = a->elt;
+	elt_b = b->elt;
 
 	sort_key = &elt_a->map->sort_key;
 
@@ -989,10 +998,8 @@ static void sort_secondary(struct tracing_map *map,
 			   struct tracing_map_sort_key *primary_key,
 			   struct tracing_map_sort_key *secondary_key)
 {
-	int (*primary_fn)(const struct tracing_map_sort_entry **,
-			  const struct tracing_map_sort_entry **);
-	int (*secondary_fn)(const struct tracing_map_sort_entry **,
-			    const struct tracing_map_sort_entry **);
+	int (*primary_fn)(const void *, const void *);
+	int (*secondary_fn)(const void *, const void *);
 	unsigned i, start = 0, n_sub = 1;
 
 	if (is_key(map, primary_key->field_idx))
@@ -1061,8 +1068,7 @@ int tracing_map_sort_entries(struct tracing_map *map,
 			     unsigned int n_sort_keys,
 			     struct tracing_map_sort_entry ***sort_entries)
 {
-	int (*cmp_entries_fn)(const struct tracing_map_sort_entry **,
-			      const struct tracing_map_sort_entry **);
+	int (*cmp_entries_fn)(const void *, const void *);
 	struct tracing_map_sort_entry *sort_entry, **entries;
 	int i, n_entries, ret;
 

base-commit: 348949d9a4440abdab3b1dc99a9bb660e8c7da7c
-- 
2.33.0.1079.g6e70778dc9-goog