[PATCH 1/5] perf jitdump: Byte-swap debug entries via unaligned-safe accessors

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

debug_entry records are packed with a variable-length name[] field, so
entries after the first may start at addresses that are not naturally
aligned for their u64 addr and int lineno/discrim fields.  On strict
alignment architectures the byte-swap loop in jit_get_next_entry()
performed misaligned 64-bit loads and stores through struct member
access, which is undefined behavior.

Use get_unaligned()/put_unaligned() for the byte-swap of each field.

Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Assisted-by: LLM
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/jitdump.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
index d25a9fe9b020ce87..e0d5cc9a828189a2 100644
--- a/tools/perf/util/jitdump.c
+++ b/tools/perf/util/jitdump.c
@@ -14,6 +14,8 @@
 #include <sys/stat.h>
 #include <sys/mman.h>
 #include <linux/stringify.h>
+#include <linux/kernel.h>
+#include <linux/unaligned.h>
 
 #include "event.h"
 #include "debug.h"
@@ -343,9 +345,14 @@ jit_get_next_entry(struct jit_buf_desc *jd)
 				/* name must be NUL-terminated within the record */
 				if (!memchr(ent->name, '\0', (char *)end - ent->name))
 					break;
-				ent->addr    = bswap_64(ent->addr);
-				ent->lineno  = bswap_32(ent->lineno);
-				ent->discrim = bswap_32(ent->discrim);
+				/*
+				 * debug entries are packed with a variable-length
+				 * name[], so entries after the first may be
+				 * unaligned: byte-swap via unaligned-safe accessors.
+				 */
+				put_unaligned(bswap_64(get_unaligned(&ent->addr)), &ent->addr);
+				put_unaligned(bswap_32(get_unaligned(&ent->lineno)), &ent->lineno);
+				put_unaligned(bswap_32(get_unaligned(&ent->discrim)), &ent->discrim);
 				ent = debug_entry_next(ent);
 			}
 			/* clamp so downstream consumers don't overrun */
-- 
2.55.0