From: Vibhav Pant <vibhavp@gmail.com>
Date: Wed, 7 Dec 2022 15:26:17 +0000 (+0530)
Subject: Make unaligned loads work with sanitization.
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=7f8aa9db63de147f4196525de99007e1e5c64dfe;p=emacs.git

Make unaligned loads work with sanitization.

Address sanitizer may miss memory bugs that happen during unaligned
loads. To prevent that, compilers may provide additional functions to
perform unaligned loads/stores, which allow sanitizer instrumentation
to check these accesses too. If the necessary header is available, and
AddressSanitizer is enabled, use them.

* configure.ac: Add check for <sanitizer/common_interface_defs.h>.
* src/lisp.h (UNALIGNED_LOAD_SIZE) [ADDRESS_SANITIZER]: New macro. If
the common sanitizer interface is available and address sanitization
is enabled, define it to __sanitizer_unaligned_load(64|32), depending
on the word size of the architecture.
* src/fns.c [HAVE_FAST_UNALIGNED_ACCESS] (Fstring_lessp): Use
'UNALIGNED_LOAD_SIZE' to perform unaligned loads from the two strings.
---

diff --git a/configure.ac b/configure.ac
index ec1729120b1..e9bca7eda26 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1842,7 +1842,8 @@ AC_CHECK_HEADERS_ONCE(
   sys/resource.h
   sys/utsname.h pwd.h utmp.h util.h
   sanitizer/lsan_interface.h
-  sanitizer/asan_interface.h])
+  sanitizer/asan_interface.h
+  sanitizer/common_interface_defs.h])
 
 AC_CACHE_CHECK([for ADDR_NO_RANDOMIZE],
   [emacs_cv_personality_addr_no_randomize],
diff --git a/src/fns.c b/src/fns.c
index d8744c1a4de..19556bf1fbc 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -497,8 +497,13 @@ Symbols are also allowed; their print names are used instead.  */)
 	  int ws = sizeof (word_t);
 	  const word_t *w1 = (const word_t *) SDATA (string1);
 	  const word_t *w2 = (const word_t *) SDATA (string2);
-	  while (b < nb - ws + 1 && w1[b / ws] == w2[b / ws])
-	    b += ws;
+	  while (b < nb - ws + 1)
+	    {
+	      if (UNALIGNED_LOAD_SIZE (w1, b / ws)
+		  != UNALIGNED_LOAD_SIZE (w2, b / ws))
+		break;
+	      b += ws;
+	    }
 	}
 
       /* Scan forward to the differing byte.  */
diff --git a/src/lisp.h b/src/lisp.h
index 0f70f60d75c..f466d4b0da5 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -5296,6 +5296,22 @@ __lsan_ignore_object (void const *p)
 }
 #endif
 
+#if defined HAVE_SANITIZER_COMMON_INTERFACE_DEFS_H \
+  && defined ADDRESS_SANITIZER
+# include <sanitizer/common_interface_defs.h>
+# if (SIZE_MAX == UINT64_MAX)
+#  define UNALIGNED_LOAD_SIZE(a, i) \
+   (size_t) __sanitizer_unaligned_load64 ((void *) ((a) + (i)))
+# elif (SIZE_MAX == UINT32_MAX)
+#  define UNALIGNED_LOAD_SIZE(a, i) \
+   (size_t) __sanitizer_unaligned_load32 ((void *) ((a) + (i)))
+# else
+#  define UNALIGNED_LOAD_SIZE(a, i) *((a) + (i))
+# endif
+#else
+# define UNALIGNED_LOAD_SIZE(a, i) *((a) + (i))
+#endif
+
 extern void xputenv (const char *);
 
 extern char *egetenv_internal (const char *, ptrdiff_t);