[PATCH v5 2/3] ring-buffer: Handle RB_MISSED_* flags on commit field correctly

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Since the MSBs of rb_data_page::commit are used for storing
RB_MISSED_EVENTS and RB_MISSED_STORED, we need to mask out those bits
when it is used for finding the size of data pages.

Fixes: 5f3b6e839f3c ("ring-buffer: Validate boot range memory events")
Fixes: 5b7be9c709e1 ("ring-buffer: Add test to validate the time stamp deltas")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 Changes in v5:
   - Do not move rb_commit_index().
   - Fix verify_event() and rb_cpu_meta_valid() too.
 Changes in v4:
   - Fix to move rb_commit_index() after ring_buffer_per_cpu definition.
---
 kernel/trace/ring_buffer.c |   27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 0eb6e6595f37..2e9b8ce6b4dc 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -395,6 +395,12 @@ static __always_inline unsigned int rb_page_commit(struct buffer_page *bpage)
 	return local_read(&bpage->page->commit);
 }
 
+/* Size is determined by what has been committed */
+static __always_inline unsigned int rb_page_size(struct buffer_page *bpage)
+{
+	return rb_page_commit(bpage) & ~RB_MISSED_MASK;
+}
+
 static void free_buffer_page(struct buffer_page *bpage)
 {
 	/* Range pages are not to be freed */
@@ -676,7 +682,7 @@ static void verify_event(struct ring_buffer_per_cpu *cpu_buffer,
 	do {
 		if (page == tail_page || WARN_ON_ONCE(stop++ > 100))
 			done = true;
-		commit = local_read(&page->page->commit);
+		commit = rb_page_size(page);
 		write = local_read(&page->write);
 		if (addr >= (unsigned long)&page->page->data[commit] &&
 		    addr < (unsigned long)&page->page->data[write])
@@ -1820,13 +1826,16 @@ static bool rb_cpu_meta_valid(struct ring_buffer_cpu_meta *meta, int cpu,
 
 	/* Is the meta buffers and the subbufs themselves have correct data? */
 	for (i = 0; i < meta->nr_subbufs; i++) {
+		unsigned long commit;
+
 		if (meta->buffers[i] < 0 ||
 		    meta->buffers[i] >= meta->nr_subbufs) {
 			pr_info("Ring buffer boot meta [%d] array out of range\n", cpu);
 			return false;
 		}
 
-		if ((unsigned)local_read(&subbuf->commit) > subbuf_size) {
+		commit = local_read(&subbuf->commit) & ~RB_MISSED_MASK;
+		if (commit > subbuf_size) {
 			pr_info("Ring buffer boot meta [%d] buffer invalid commit\n", cpu);
 			return false;
 		}
@@ -1907,7 +1916,7 @@ static int rb_validate_buffer(struct buffer_data_page *dpage, int cpu)
 	u64 delta;
 	int tail;
 
-	tail = local_read(&dpage->commit);
+	tail = local_read(&dpage->commit) & ~RB_MISSED_MASK;
 	return rb_read_data_buffer(dpage, tail, cpu, &ts, &delta);
 }
 
@@ -1934,7 +1943,7 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 		goto invalid;
 	}
 	entries += ret;
-	entry_bytes += local_read(&cpu_buffer->reader_page->page->commit);
+	entry_bytes += rb_page_size(cpu_buffer->reader_page);
 	local_set(&cpu_buffer->reader_page->entries, ret);
 
 	ts = head_page->page->time_stamp;
@@ -2054,7 +2063,7 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 			local_inc(&cpu_buffer->pages_touched);
 
 		entries += ret;
-		entry_bytes += local_read(&head_page->page->commit);
+		entry_bytes += rb_page_size(head_page);
 		local_set(&cpu_buffer->head_page->entries, ret);
 
 		if (head_page == cpu_buffer->commit_page)
@@ -3256,12 +3265,6 @@ rb_iter_head_event(struct ring_buffer_iter *iter)
 	return NULL;
 }
 
-/* Size is determined by what has been committed */
-static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
-{
-	return rb_page_commit(bpage) & ~RB_MISSED_MASK;
-}
-
 static __always_inline unsigned
 rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
 {
@@ -4432,7 +4435,7 @@ static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
 
 	if (tail == CHECK_FULL_PAGE) {
 		full = true;
-		tail = local_read(&bpage->commit);
+		tail = local_read(&bpage->commit) & ~RB_MISSED_MASK;
 	} else if (info->add_timestamp &
 		   (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE)) {
 		/* Ignore events with absolute time stamps */