ring-buffer: Add magic and struct size to boot up meta data

Add a magic number as well as save the struct size of the ring_buffer_meta
structure in the meta data to also use as validation. Updating the magic
number could be used to force a invalidation between kernel versions, and
saving the structure size is also a good method to make sure the content
is what is expected.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Vincent Donnefort <vdonnefort@google.com>
Link: https://lore.kernel.org/20240815115032.0c197b32@rorschach.local.home
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index b16f301b8a9339addcb7f597f9cc6fd969d23d2e..c3a5e6cbb9403c4c7e3669d929d8f33e63857b41 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -44,7 +44,11 @@
 
 static void update_pages_handler(struct work_struct *work);
 
+#define RING_BUFFER_META_MAGIC 0xBADFEED
+
 struct ring_buffer_meta {
+       int             magic;
+       int             struct_size;
        unsigned long   text_addr;
        unsigned long   data_addr;
        unsigned long   first_buffer;
@@ -1627,6 +1631,13 @@ static bool rb_meta_valid(struct ring_buffer_meta *meta, int cpu,
        unsigned long buffers_end;
        int i;
 
+       /* Check the meta magic and meta struct size */
+       if (meta->magic != RING_BUFFER_META_MAGIC ||
+           meta->struct_size != sizeof(*meta)) {
+               pr_info("Ring buffer boot meta[%d] mismatch of magic or struct size\n", cpu);
+               return false;
+       }
+
        /* The subbuffer's size and number of subbuffers must match */
        if (meta->subbuf_size != subbuf_size ||
            meta->nr_subbufs != nr_pages + 1) {
@@ -1858,6 +1869,9 @@ static void rb_range_meta_init(struct trace_buffer *buffer, int nr_pages)
 
                memset(meta, 0, next_meta - (void *)meta);
 
+               meta->magic = RING_BUFFER_META_MAGIC;
+               meta->struct_size = sizeof(*meta);
+
                meta->nr_subbufs = nr_pages + 1;
                meta->subbuf_size = PAGE_SIZE;