[PATCH] perf/x86: Annotate struct bts_buffer with __counted_by()

[Thorsten Blum <thorsten.blum@linux.dev>]

Add the __counted_by() compiler attribute to the flexible array member
buf to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Use struct_size() to calculate the number of bytes to allocate for a new
bts_buffer. Compared to offsetof(), struct_size() has additional
compile-time checks (e.g., __must_be_array()).

No functional changes intended.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 arch/x86/events/intel/bts.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index 8f78b0c900ef..2888edb3f7c5 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -58,7 +58,7 @@ struct bts_buffer {
 	local_t		head;
 	unsigned long	end;
 	void		**data_pages;
-	struct bts_phys	buf[];
+	struct bts_phys	buf[] __counted_by(nr_bufs);
 };
 
 static struct pmu bts_pmu;
@@ -101,7 +101,7 @@ bts_buffer_setup_aux(struct perf_event *event, void **pages,
 	if (overwrite && nbuf > 1)
 		return NULL;
 
-	buf = kzalloc_node(offsetof(struct bts_buffer, buf[nbuf]), GFP_KERNEL, node);
+	buf = kzalloc_node(struct_size(buf, buf, nbuf), GFP_KERNEL, node);
 	if (!buf)
 		return NULL;
 
-- 
2.48.1