tracing: Have persistent trace instances save KASLR offset

There's no reason to save the KASLR offset for the ring buffer itself.
That is used by the tracer. Now that the tracer has a way to save data in
the persistent memory of the ring buffer, have the tracing infrastructure
take care of the saving of the KASLR offset.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://lore.kernel.org/20250305164608.792722274@goodmis.org
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 32 insertions, 5 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 73c8df12c33c..d4df56657b9d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5988,8 +5988,14 @@ ssize_t tracing_resize_ring_buffer(struct trace_array *tr,
 	return __tracing_resize_ring_buffer(tr, size, cpu_id);
 }
 
+struct trace_scratch {
+	unsigned long		kaslr_addr;
+};
+
 static void update_last_data(struct trace_array *tr)
 {
+	struct trace_scratch *tscratch;
+
 	if (!(tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
 		return;
 
@@ -6004,6 +6010,17 @@ static void update_last_data(struct trace_array *tr)
 	/* Using current data now */
 	tr->text_delta = 0;
 
+	if (!tr->scratch)
+		return;
+
+	tscratch = tr->scratch;
+
+	/* Set the persistent ring buffer meta data to this address */
+#ifdef CONFIG_RANDOMIZE_BASE
+	tscratch->kaslr_addr = kaslr_offset();
+#else
+	tscratch->kaslr_addr = 0;
+#endif
 	tr->flags &= ~TRACE_ARRAY_FL_LAST_BOOT;
 }
 
@@ -6817,6 +6834,7 @@ static ssize_t
 tracing_last_boot_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
 {
 	struct trace_array *tr = filp->private_data;
+	struct trace_scratch *tscratch = tr->scratch;
 	struct seq_buf seq;
 	char buf[64];
 
@@ -6829,8 +6847,8 @@ tracing_last_boot_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t
 	 * Otherwise it shows the KASLR address from the previous boot which
 	 * should not be the same as the current boot.
 	 */
-	if (tr->flags & TRACE_ARRAY_FL_LAST_BOOT)
-		seq_buf_printf(&seq, "%lx\t[kernel]\n", tr->kaslr_addr);
+	if (tscratch && (tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
+		seq_buf_printf(&seq, "%lx\t[kernel]\n", tscratch->kaslr_addr);
 	else
 		seq_buf_puts(&seq, "# Current\n");
 
@@ -9210,6 +9228,8 @@ static int
 allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size)
 {
 	enum ring_buffer_flags rb_flags;
+	struct trace_scratch *tscratch;
+	unsigned int scratch_size;
 
 	rb_flags = tr->trace_flags & TRACE_ITER_OVERWRITE ? RB_FL_OVERWRITE : 0;
 
@@ -9218,12 +9238,19 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size
 	if (tr->range_addr_start && tr->range_addr_size) {
 		buf->buffer = ring_buffer_alloc_range(size, rb_flags, 0,
 						      tr->range_addr_start,
-						      tr->range_addr_size, 0);
+						      tr->range_addr_size,
+						      sizeof(*tscratch));
+
+		tscratch = ring_buffer_meta_scratch(buf->buffer, &scratch_size);
+		if (tscratch) {
+			tr->scratch = tscratch;
+			tr->scratch_size = scratch_size;
 
 #ifdef CONFIG_RANDOMIZE_BASE
-		if (ring_buffer_last_boot_delta(buf->buffer, &tr->kaslr_addr))
-			tr->text_delta = kaslr_offset() - tr->kaslr_addr;
+			if (tscratch->kaslr_addr)
+				tr->text_delta = kaslr_offset() - tscratch->kaslr_addr;
 #endif
+		}
 		/*
 		 * This is basically the same as a mapped buffer,
 		 * with the same restrictions.