fortify-headers

commit b2c20e6c16278fe556ce4c4ff7d3b146b3a8f009
parent b9bd9400d2a6a4484ef92d708f363b9e8d0e3cb7
Author: jvoisin <julien.voisin@dustri.org>
Date:   Mon, 11 Sep 2023 20:23:12 +0200

Factorize overlap checks into a macro

Diffstat:
M
include/fortify-headers.h
 | 
9
+++++++++
M
include/string.h
 | 
25
+++++--------------------

2 files changed, 14 insertions(+), 20 deletions(-)
diff --git a/include/fortify-headers.h b/include/fortify-headers.h
@@ -123,6 +123,15 @@
 
 #endif /* __has_attribute */
 
+//TODO(jvoisin) Add a check for overflows
+/* check if pointers are overlapping but not if dst == src,
+ * since gcc seems to like to generate code that relies on dst == src */
+#define __fh_overlap(a, b, l) \
+	( \
+		((a) < (b) && (b) < (a) + (size_t)(l)) \
+	     || ((b) < (a) && (a) < (b) + (size_t)(l)) \
+        )
+
 /*
  * We're not making use of C23's <stdckdint.h> since:
  *   - there is no elegant way to make it ignore the results.
diff --git a/include/string.h b/include/string.h
@@ -49,10 +49,7 @@ _FORTIFY_FN(memcpy) void *memcpy(void * _FORTIFY_POS0 __od,
 	char *__d = (char *)__od;
 	const char *__s = (const char *)__os;
 
-	/* trap if pointers are overlapping but not if dst == src.
-	 * gcc seems to like to generate code that relies on dst == src */
-	if ((__d < __s && __d + __n > __s) ||
-	    (__s < __d && __s + __n > __d))
+	if __fh_overlap(__d, __s, __n)
 		__builtin_trap();
 	if (__n > __bd || __n > __bs)
 		__builtin_trap();
@@ -131,10 +128,7 @@ _FORTIFY_FN(stpcpy) char *stpcpy(char * _FORTIFY_POS0 __d, const char *__s)
 {
 	size_t __n = strlen(__s) + 1;
 
-	/* trap if pointers are overlapping but not if dst == src.
-	 * gcc seems to like to generate code that relies on dst == src */
-	if ((__d < __s && __d + __n > __s) ||
-	    (__s < __d && __s + __n > __d))
+	if (__fh_overlap(__d, __s, __n))
 		__builtin_trap();
 
 	size_t __b = __bos(__d, 0);
@@ -150,10 +144,7 @@ __diagnose_as_builtin(__builtin_stpncpy, 1, 2, 3)
 _FORTIFY_FN(stpncpy) char *stpncpy(char * _FORTIFY_POS0 __d, const char *__s,
                                    size_t __n)
 {
-	/* trap if pointers are overlapping but not if dst == src.
-	 * gcc seems to like to generate code that relies on dst == src */
-	if ((__d < __s && __d + __n > __s) ||
-	    (__s < __d && __s + __n > __d))
+	if (__fh_overlap(__d, __s, __n))
 		__builtin_trap();
 
 	size_t __b = __bos(__d, 0);
@@ -182,10 +173,7 @@ _FORTIFY_FN(strcpy) char *strcpy(char * _FORTIFY_POS0 __d, const char *__s)
 {
 	size_t __n = strlen(__s) + 1;
 
-	/* trap if pointers are overlapping but not if dst == src.
-	 * gcc seems to like to generate code that relies on dst == src */
-	if ((__d < __s && __d + __n > __s) ||
-	    (__s < __d && __s + __n > __d))
+	if (__fh_overlap(__d, __s, __n))
 		__builtin_trap();
 
 	size_t __b = __bos(__d, 0);
@@ -219,10 +207,7 @@ __diagnose_as_builtin(__builtin_strncpy, 1, 2, 3)
 _FORTIFY_FN(strncpy) char *strncpy(char * _FORTIFY_POS0 __d,
                                    const char *__s, size_t __n)
 {
-	/* trap if pointers are overlapping but not if dst == src.
-	 * gcc seems to like to generate code that relies on dst == src */
-	if ((__d < __s && __d + __n > __s) ||
-	    (__s < __d && __s + __n > __d))
+	if (__fh_overlap(__d, __s, __n))
 		__builtin_trap();
 
 	size_t __b = __bos(__d, 0);