Message-Id: <20241026161413.222898-1-niharchaithanya@gmail.com>
Date: Sat, 26 Oct 2024 21:44:17 +0530
From: Nihar Chaithanya <niharchaithanya@...il.com>
To: ryabinin.a.a@...il.com
Cc: andreyknvl@...il.com,
	dvyukov@...gle.com,
	glider@...gle.com,
	elver@...gle.com,
	skhan@...uxfoundation.org,
	kasan-dev@...glegroups.com,
	linux-kernel@...r.kernel.org,
	Nihar Chaithanya <niharchaithanya@...il.com>
Subject: [PATCH v3] kasan: report: filter out kasan related stack entries

The reports of KASAN include KASAN related stack frames which are not
the point of interest in the stack-trace. KCSAN report filters out such
internal frames providing relevant stack trace. Currently, KASAN reports
are generated by dump_stack_lvl() which prints the entire stack.

Add functionality to KASAN reports to save the stack entries and filter
out the kasan related stack frames in place of dump_stack_lvl() and
stack_depot_print().

Within this new functionality:
	- A function kasan_dump_stack_lvl() in place of dump_stack_lvl() is
	  created which contains functionality for saving, filtering and
	  printing the stack-trace.
	- A function kasan_stack_depot_print() in place of
	  stack_depot_print() is created which contains functionality for
	  filtering and printing the stack-trace.
	- The get_stack_skipnr() function which employs pattern based stack
	  filtering is included.
	- The replace_stack_entry() function which uses ip value based
	  stack filtering is included.

Signed-off-by: Nihar Chaithanya <niharchaithanya@...il.com>
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=215756
---
Changes in v2:
        - Changed the function name from save_stack_lvl_kasan() to
          kasan_dump_stack_lvl().
        - Added filtering of stack frames for print_track() with
          kasan_stack_depot_print().
        - Removed redundant print_stack_trace(), and instead using
          stack_trace_print() directly.
        - Removed sanitize_stack_entries() and replace_stack_entry()
          functions.
        - Increased the buffer size in get_stack_skipnr to 128.

Changes in v3:
	- Included an additional criteria for pattern based filtering
	  in get_stack_skipnr().
	- Included ip value based stack filtering with the functions
	  sanitize_stack_entries() and replace_stack_entry().
	- Corrected the comments and name of the newly added functions
	  kasan_dump_stack() and kasan_stack_depot_print().

 mm/kasan/report.c | 111 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 107 insertions(+), 4 deletions(-)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 3e48668c3e40..648a89fea3e7 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -261,6 +261,110 @@ static void print_error_description(struct kasan_report_info *info)
 			info->access_addr, current->comm, task_pid_nr(current));
 }
 
+/* Helper to skip KASAN-related functions in stack-trace. */
+static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries)
+{
+	char buf[64];
+	int len, skip;
+
+	for (skip = 0; skip < num_entries; ++skip) {
+		len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]);
+
+		/* Never show  kasan_* or __kasan_* functions. */
+		if ((strnstr(buf, "kasan_", len) == buf) ||
+			(strnstr(buf, "__kasan_", len) == buf))
+			continue;
+		/*
+		 * No match for runtime functions -- @skip entries to skip to
+		 * get to first frame of interest.
+		 */
+		break;
+	}
+
+	return skip;
+}
+
+/*
+ * Skips to the first entry that matches the function of @ip, and then replaces
+ * that entry with @ip, returning the entries to skip with @replaced containing
+ * the replaced entry.
+ */
+static int
+replace_stack_entry(unsigned long stack_entries[], int num_entries, unsigned long ip,
+		    unsigned long *replaced)
+{
+	unsigned long symbolsize, offset;
+	unsigned long target_func;
+	int skip;
+
+	if (kallsyms_lookup_size_offset(ip, &symbolsize, &offset))
+		target_func = ip - offset;
+	else
+		goto fallback;
+
+	for (skip = 0; skip < num_entries; ++skip) {
+		unsigned long func = stack_entries[skip];
+
+		if (!kallsyms_lookup_size_offset(func, &symbolsize, &offset))
+			goto fallback;
+		func -= offset;
+
+		if (func == target_func) {
+			*replaced = stack_entries[skip];
+			stack_entries[skip] = ip;
+			return skip;
+		}
+	}
+
+fallback:
+	/* Should not happen; the resulting stack trace is likely misleading. */
+	WARN_ONCE(1, "Cannot find frame for %pS in stack trace", (void *)ip);
+	return get_stack_skipnr(stack_entries, num_entries);
+}
+
+static int
+sanitize_stack_entries(unsigned long stack_entries[], int num_entries, unsigned long ip,
+		       unsigned long *replaced)
+{
+	return ip ? replace_stack_entry(stack_entries, num_entries, ip, replaced) :
+			  get_stack_skipnr(stack_entries, num_entries);
+}
+
+/*
+ * Use in place of dump_stack() to filter out KASAN-related frames in
+ * the stack trace.
+ */
+static void kasan_dump_stack(unsigned long ip)
+{
+	unsigned long reordered_to = 0;
+	unsigned long stack_entries[KASAN_STACK_DEPTH] = { 0 };
+
+	int num_stack_entries = stack_trace_save(stack_entries, KASAN_STACK_DEPTH, 0);
+	int skipnr = sanitize_stack_entries(stack_entries, num_stack_entries,
+										ip, &reordered_to);
+
+	dump_stack_print_info(KERN_ERR);
+	stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0);
+}
+
+/*
+ * Use in place of stack_depot_print() to filter out KASAN-related frames
+ * in the stack trace.
+ */
+static void kasan_stack_depot_print(depot_stack_handle_t stack)
+{
+	unsigned int nr_entries;
+	unsigned long *entries = NULL;
+	unsigned int skipnr;
+
+	nr_entries = stack_depot_fetch(stack, &entries);
+	if (nr_entries) {
+		skipnr = get_stack_skipnr(entries, nr_entries);
+		stack_trace_print(entries + skipnr, nr_entries - skipnr, 0);
+	} else
+		pr_err("(stack is not available)\n");
+}
+
 static void print_track(struct kasan_track *track, const char *prefix)
 {
 #ifdef CONFIG_KASAN_EXTRA_INFO
@@ -277,7 +381,7 @@ static void print_track(struct kasan_track *track, const char *prefix)
 	pr_err("%s by task %u:\n", prefix, track->pid);
 #endif /* CONFIG_KASAN_EXTRA_INFO */
 	if (track->stack)
-		stack_depot_print(track->stack);
+		kasan_stack_depot_print(track->stack);
 	else
 		pr_err("(stack is not available)\n");
 }
@@ -374,7 +478,6 @@ static void print_address_description(void *addr, u8 tag,
 {
 	struct page *page = addr_to_page(addr);
 
-	dump_stack_lvl(KERN_ERR);
 	pr_err("\n");
 
 	if (info->cache && info->object) {
@@ -484,11 +587,11 @@ static void print_report(struct kasan_report_info *info)
 		kasan_print_tags(tag, info->first_bad_addr);
 	pr_err("\n");
 
+	kasan_dump_stack(info->ip);
+
 	if (addr_has_metadata(addr)) {
 		print_address_description(addr, tag, info);
 		print_memory_metadata(info->first_bad_addr);
-	} else {
-		dump_stack_lvl(KERN_ERR);
 	}
 }
 
-- 
2.34.1

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