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>

include/linux/ring_buffer.h

@@ -95,7 +95,6 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag
 					       unsigned long scratch_size,
 					       struct lock_class_key *key);
 
-bool ring_buffer_last_boot_delta(struct trace_buffer *buffer, unsigned long *kaslr_addr);
 void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size);
 
 /*

kernel/trace/ring_buffer.c

@@ -55,7 +55,6 @@ struct ring_buffer_meta {
 };
 
 struct ring_buffer_cpu_meta {
-	unsigned long	kaslr_addr;
 	unsigned long	first_buffer;
 	unsigned long	head_buffer;
 	unsigned long	commit_buffer;
@@ -557,8 +556,6 @@ struct trace_buffer {
 
 	struct ring_buffer_meta		*meta;
 
-	unsigned long			kaslr_addr;
-
 	unsigned int			subbuf_size;
 	unsigned int			subbuf_order;
 	unsigned int			max_data_size;
@@ -1949,15 +1946,6 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 	}
 }
 
-static void rb_meta_init_text_addr(struct ring_buffer_cpu_meta *meta)
-{
-#ifdef CONFIG_RANDOMIZE_BASE
-	meta->kaslr_addr = kaslr_offset();
-#else
-	meta->kaslr_addr = 0;
-#endif
-}
-
 static void rb_range_meta_init(struct trace_buffer *buffer, int nr_pages, int scratch_size)
 {
 	struct ring_buffer_cpu_meta *meta;
@@ -1990,7 +1978,6 @@ static void rb_range_meta_init(struct trace_buffer *buffer, int nr_pages, int sc
 			meta->first_buffer += delta;
 			meta->head_buffer += delta;
 			meta->commit_buffer += delta;
-			buffer->kaslr_addr = meta->kaslr_addr;
 			continue;
 		}
 
@@ -2007,7 +1994,6 @@ static void rb_range_meta_init(struct trace_buffer *buffer, int nr_pages, int sc
 		subbuf = rb_subbufs_from_meta(meta);
 
 		meta->first_buffer = (unsigned long)subbuf;
-		rb_meta_init_text_addr(meta);
 
 		/*
 		 * The buffers[] array holds the order of the sub-buffers
@@ -2549,35 +2535,22 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag
 			    scratch_size, key);
 }
 
-/**
- * ring_buffer_last_boot_delta - return the delta offset from last boot
- * @buffer: The buffer to return the delta from
- * @text: Return text delta
- * @data: Return data delta
- *
- * Returns: The true if the delta is non zero
- */
-bool ring_buffer_last_boot_delta(struct trace_buffer *buffer, unsigned long *kaslr_addr)
-{
-	if (!buffer)
-		return false;
-
-	if (!buffer->kaslr_addr)
-		return false;
-
-	*kaslr_addr = buffer->kaslr_addr;
-
-	return true;
-}
-
 void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size)
 {
+	struct ring_buffer_meta *meta;
+	void *ptr;
+
 	if (!buffer || !buffer->meta)
 		return NULL;
 
-	*size = PAGE_SIZE - sizeof(*buffer->meta);
+	meta = buffer->meta;
 
-	return (void *)buffer->meta + sizeof(*buffer->meta);
+	ptr = (void *)ALIGN((unsigned long)meta + sizeof(*meta), sizeof(long));
+
+	if (size)
+		*size = (void *)meta + meta->buffers_offset - ptr;
+
+	return ptr;
 }
 
 /**
@@ -6133,7 +6106,6 @@ static void reset_disabled_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
-	struct ring_buffer_cpu_meta *meta;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return;
@@ -6152,11 +6124,6 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
 	atomic_dec(&cpu_buffer->record_disabled);
 	atomic_dec(&cpu_buffer->resize_disabled);
 
-	/* Make sure persistent meta now uses this buffer's addresses */
-	meta = rb_range_meta(buffer, 0, cpu_buffer->cpu);
-	if (meta)
-		rb_meta_init_text_addr(meta);
-
 	mutex_unlock(&buffer->mutex);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
@@ -6171,7 +6138,6 @@ EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
 void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
-	struct ring_buffer_cpu_meta *meta;
 	int cpu;
 
 	/* prevent another thread from changing buffer sizes */
@@ -6199,11 +6165,6 @@ void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
 
 		reset_disabled_cpu_buffer(cpu_buffer);
 
-		/* Make sure persistent meta now uses this buffer's addresses */
-		meta = rb_range_meta(buffer, 0, cpu_buffer->cpu);
-		if (meta)
-			rb_meta_init_text_addr(meta);
-
 		atomic_dec(&cpu_buffer->record_disabled);
 		atomic_sub(RESET_BIT, &cpu_buffer->resize_disabled);
 	}

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.

kernel/trace/trace.h

@@ -348,8 +348,11 @@ struct trace_array {
 	unsigned int		mapped;
 	unsigned long		range_addr_start;
 	unsigned long		range_addr_size;
-	unsigned long		kaslr_addr;
 	long			text_delta;
+	void			*scratch; /* pointer in persistent memory */
+	int			scratch_size;
+
+	int			buffer_disabled;
 
 	struct trace_pid_list	__rcu *filtered_pids;
 	struct trace_pid_list	__rcu *filtered_no_pids;
@@ -367,7 +370,6 @@ struct trace_array {
 	 * CONFIG_TRACER_MAX_TRACE.
 	 */
 	arch_spinlock_t		max_lock;
-	int			buffer_disabled;
 #ifdef CONFIG_FTRACE_SYSCALLS
 	int			sys_refcount_enter;
 	int			sys_refcount_exit;