tracing: Handle old buffer mappings for event strings and functions

Use the saved text_delta and data_delta of a persistent memory mapped ring
buffer that was saved from a previous boot, and use the delta in the trace
event print output so that strings and functions show up normally.

That is, for an event like trace_kmalloc() that prints the callsite via
"%pS", if it used the address saved in the ring buffer it will not match
the function that was saved in the previous boot if the kernel remaps
itself between boots.

For RCU events that point to saved static strings where only the address
of the string is saved in the ring buffer, it too will be adjusted to
point to where the string is on the current boot.

Link: https://lkml.kernel.org/r/[email protected]

Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Vincent Donnefort <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Daniel Bristot de Oliveira <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vineeth Pillai <[email protected]>
Cc: Youssef Esmat <[email protected]>
Cc: Beau Belgrave <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: David Howells <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Guenter Roeck <[email protected]>
Cc: Ross Zwisler <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: rostedt

kernel/trace/trace.c

@@ -3671,8 +3671,11 @@ static void test_can_verify(void)
 void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
 			 va_list ap)
 {
+	long text_delta = iter->tr->text_delta;
+	long data_delta = iter->tr->data_delta;
 	const char *p = fmt;
 	const char *str;
+	bool good;
 	int i, j;
 
 	if (WARN_ON_ONCE(!fmt))
@@ -3691,7 +3694,10 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
 
 		j = 0;
 
-		/* We only care about %s and variants */
+		/*
+		 * We only care about %s and variants
+		 * as well as %p[sS] if delta is non-zero
+		 */
 		for (i = 0; p[i]; i++) {
 			if (i + 1 >= iter->fmt_size) {
 				/*
@@ -3720,6 +3726,11 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
 				}
 				if (p[i+j] == 's')
 					break;
+
+				if (text_delta && p[i+1] == 'p' &&
+				    ((p[i+2] == 's' || p[i+2] == 'S')))
+					break;
+
 				star = false;
 			}
 			j = 0;
@@ -3733,6 +3744,24 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
 		iter->fmt[i] = '\0';
 		trace_seq_vprintf(&iter->seq, iter->fmt, ap);
 
+		/* Add delta to %pS pointers */
+		if (p[i+1] == 'p') {
+			unsigned long addr;
+			char fmt[4];
+
+			fmt[0] = '%';
+			fmt[1] = 'p';
+			fmt[2] = p[i+2]; /* Either %ps or %pS */
+			fmt[3] = '\0';
+
+			addr = va_arg(ap, unsigned long);
+			addr += text_delta;
+			trace_seq_printf(&iter->seq, fmt, (void *)addr);
+
+			p += i + 3;
+			continue;
+		}
+
 		/*
 		 * If iter->seq is full, the above call no longer guarantees
 		 * that ap is in sync with fmt processing, and further calls
@@ -3751,6 +3780,14 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
 		/* The ap now points to the string data of the %s */
 		str = va_arg(ap, const char *);
 
+		good = trace_safe_str(iter, str, star, len);
+
+		/* Could be from the last boot */
+		if (data_delta && !good) {
+			str += data_delta;
+			good = trace_safe_str(iter, str, star, len);
+		}
+
 		/*
 		 * If you hit this warning, it is likely that the
 		 * trace event in question used %s on a string that
@@ -3760,8 +3797,7 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
 		 * instead. See samples/trace_events/trace-events-sample.h
 		 * for reference.
 		 */
-		if (WARN_ONCE(!trace_safe_str(iter, str, star, len),
-			      "fmt: '%s' current_buffer: '%s'",
+		if (WARN_ONCE(!good, "fmt: '%s' current_buffer: '%s'",
 			      fmt, seq_buf_str(&iter->seq.seq))) {
 			int ret;