[PATCH 1/2] kcsan: Fix function matching in report

[PATCH 1/2] kcsan: Fix function matching in report

[Marco Elver]

Pass string length as returned by scnprintf() to strnstr(), since
strnstr() searches exactly len bytes in haystack, even if it contains a
NUL-terminator before haystack+len.

Signed-off-by: Marco Elver <elver@google.com>
---
 kernel/kcsan/report.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index ddc18f1224a4..cf41d63dd0cd 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -192,11 +192,11 @@ skip_report(enum kcsan_value_change value_change, unsigned long top_frame)
 		 * maintainers.
 		 */
 		char buf[64];
+		int len = scnprintf(buf, sizeof(buf), "%ps", (void *)top_frame);
 
-		snprintf(buf, sizeof(buf), "%ps", (void *)top_frame);
-		if (!strnstr(buf, "rcu_", sizeof(buf)) &&
-		    !strnstr(buf, "_rcu", sizeof(buf)) &&
-		    !strnstr(buf, "_srcu", sizeof(buf)))
+		if (!strnstr(buf, "rcu_", len) &&
+		    !strnstr(buf, "_rcu", len) &&
+		    !strnstr(buf, "_srcu", len))
 			return true;
 	}
 
@@ -262,15 +262,15 @@ static const char *get_thread_desc(int task_id)
 static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries)
 {
 	char buf[64];
+	int len;
 	int skip = 0;
 
 	for (; skip < num_entries; ++skip) {
-		snprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]);
-		if (!strnstr(buf, "csan_", sizeof(buf)) &&
-		    !strnstr(buf, "tsan_", sizeof(buf)) &&
-		    !strnstr(buf, "_once_size", sizeof(buf))) {
+		len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]);
+		if (!strnstr(buf, "csan_", len) &&
+		    !strnstr(buf, "tsan_", len) &&
+		    !strnstr(buf, "_once_size", len))
 			break;
-		}
 	}
 	return skip;
 }
-- 
2.26.0.110.g2183baf09c-goog

[PATCH 2/2] kcsan: Make reporting aware of KCSAN tests

[Marco Elver]

Reporting hides KCSAN runtime functions in the stack trace, with
filtering done based on function names. Currently this included all
functions (or modules) that would match "kcsan_". Make the filter aware
of KCSAN tests, which contain "kcsan_test", and are no longer skipped in
the report.

This is in preparation for adding a KCSAN test module.

Signed-off-by: Marco Elver <elver@google.com>
---
 kernel/kcsan/report.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index cf41d63dd0cd..ac5f8345bae9 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -262,16 +262,32 @@ static const char *get_thread_desc(int task_id)
 static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries)
 {
 	char buf[64];
-	int len;
-	int skip = 0;
+	char *cur;
+	int len, skip;
 
-	for (; skip < num_entries; ++skip) {
+	for (skip = 0; skip < num_entries; ++skip) {
 		len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]);
-		if (!strnstr(buf, "csan_", len) &&
-		    !strnstr(buf, "tsan_", len) &&
-		    !strnstr(buf, "_once_size", len))
-			break;
+
+		/* Never show tsan_* or {read,write}_once_size. */
+		if (strnstr(buf, "tsan_", len) ||
+		    strnstr(buf, "_once_size", len))
+			continue;
+
+		cur = strnstr(buf, "kcsan_", len);
+		if (cur) {
+			cur += sizeof("kcsan_") - 1;
+			if (strncmp(cur, "test", sizeof("test") - 1))
+				continue; /* KCSAN runtime function. */
+			/* KCSAN related test. */
+		}
+
+		/*
+		 * No match for runtime functions -- @skip entries to skip to
+		 * get to first frame of interest.
+		 */
+		break;
 	}
+
 	return skip;
 }
 
-- 
2.26.0.110.g2183baf09c-goog

Re: [PATCH 1/2] kcsan: Fix function matching in report

[Paul E. McKenney]

On Fri, Apr 10, 2020 at 06:44:17PM +0200, Marco Elver wrote:
> Pass string length as returned by scnprintf() to strnstr(), since
> strnstr() searches exactly len bytes in haystack, even if it contains a
> NUL-terminator before haystack+len.
> 
> Signed-off-by: Marco Elver <elver@google.com>

I queued both for testing and review, thank you, Marco!

							Thanx, Paul

> ---
>  kernel/kcsan/report.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
> index ddc18f1224a4..cf41d63dd0cd 100644
> --- a/kernel/kcsan/report.c
> +++ b/kernel/kcsan/report.c
> @@ -192,11 +192,11 @@ skip_report(enum kcsan_value_change value_change, unsigned long top_frame)
>  		 * maintainers.
>  		 */
>  		char buf[64];
> +		int len = scnprintf(buf, sizeof(buf), "%ps", (void *)top_frame);
>  
> -		snprintf(buf, sizeof(buf), "%ps", (void *)top_frame);
> -		if (!strnstr(buf, "rcu_", sizeof(buf)) &&
> -		    !strnstr(buf, "_rcu", sizeof(buf)) &&
> -		    !strnstr(buf, "_srcu", sizeof(buf)))
> +		if (!strnstr(buf, "rcu_", len) &&
> +		    !strnstr(buf, "_rcu", len) &&
> +		    !strnstr(buf, "_srcu", len))
>  			return true;
>  	}
>  
> @@ -262,15 +262,15 @@ static const char *get_thread_desc(int task_id)
>  static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries)
>  {
>  	char buf[64];
> +	int len;
>  	int skip = 0;
>  
>  	for (; skip < num_entries; ++skip) {
> -		snprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]);
> -		if (!strnstr(buf, "csan_", sizeof(buf)) &&
> -		    !strnstr(buf, "tsan_", sizeof(buf)) &&
> -		    !strnstr(buf, "_once_size", sizeof(buf))) {
> +		len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]);
> +		if (!strnstr(buf, "csan_", len) &&
> +		    !strnstr(buf, "tsan_", len) &&
> +		    !strnstr(buf, "_once_size", len))
>  			break;
> -		}
>  	}
>  	return skip;
>  }
> -- 
> 2.26.0.110.g2183baf09c-goog
>