Merge tag 'hardening-v6.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull kernel hardening updates from Kees Cook:
 "Most of the collected changes here are fixes across the tree for
  various hardening features (details noted below).

  The most notable new feature here is the addition of the memcpy()
  overflow warning (under CONFIG_FORTIFY_SOURCE), which is the next step
  on the path to killing the common class of "trivially detectable"
  buffer overflow conditions (i.e. on arrays with sizes known at compile
  time) that have resulted in many exploitable vulnerabilities over the
  years (e.g. BleedingTooth).

  This feature is expected to still have some undiscovered false
  positives. It's been in -next for a full development cycle and all the
  reported false positives have been fixed in their respective trees.
  All the known-bad code patterns we could find with Coccinelle are also
  either fixed in their respective trees or in flight.

  The commit message in commit 54d9469bc515 ("fortify: Add run-time WARN
  for cross-field memcpy()") for the feature has extensive details, but
  I'll repeat here that this is a warning _only_, and is not intended to
  actually block overflows (yet). The many patches fixing array sizes
  and struct members have been landing for several years now, and we're
  finally able to turn this on to find any remaining stragglers.

  Summary:

  Various fixes across several hardening areas:

   - loadpin: Fix verity target enforcement (Matthias Kaehlcke).

   - zero-call-used-regs: Add missing clobbers in paravirt (Bill
     Wendling).

   - CFI: clean up sparc function pointer type mismatches (Bart Van
     Assche).

   - Clang: Adjust compiler flag detection for various Clang changes
     (Sami Tolvanen, Kees Cook).

   - fortify: Fix warnings in arch-specific code in sh, ARM, and xen.

  Improvements to existing features:

   - testing: improve overflow KUnit test, introduce fortify KUnit test,
     add more coverage to LKDTM tests (Bart Van Assche, Kees Cook).

   - overflow: Relax overflow type checking for wider utility.

  New features:

   - string: Introduce strtomem() and strtomem_pad() to fill a gap in
     strncpy() replacement needs.

   - um: Enable FORTIFY_SOURCE support.

   - fortify: Enable run-time struct member memcpy() overflow warning"

* tag 'hardening-v6.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: (27 commits)
  Makefile.extrawarn: Move -Wcast-function-type-strict to W=1
  hardening: Remove Clang's enable flag for -ftrivial-auto-var-init=zero
  sparc: Unbreak the build
  x86/paravirt: add extra clobbers with ZERO_CALL_USED_REGS enabled
  x86/paravirt: clean up typos and grammaros
  fortify: Convert to struct vs member helpers
  fortify: Explicitly check bounds are compile-time constants
  x86/entry: Work around Clang __bdos() bug
  ARM: decompressor: Include .data.rel.ro.local
  fortify: Adjust KUnit test for modular build
  sh: machvec: Use char[] for section boundaries
  kunit/memcpy: Avoid pathological compile-time string size
  lib: Improve the is_signed_type() kunit test
  LoadPin: Require file with verity root digests to have a header
  dm: verity-loadpin: Only trust verity targets with enforcement
  LoadPin: Fix Kconfig doc about format of file with verity digests
  um: Enable FORTIFY_SOURCE
  lkdtm: Update tests for memcpy() run-time warnings
  fortify: Add run-time WARN for cross-field memcpy()
  fortify: Use SIZE_MAX instead of (size_t)-1
  ...

1 files changed, 178 insertions, 67 deletions

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 3b401fa0f374..b62c90cfafaf 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -2,7 +2,9 @@
 #ifndef _LINUX_FORTIFY_STRING_H_
 #define _LINUX_FORTIFY_STRING_H_
 
+#include <linux/bug.h>
 #include <linux/const.h>
+#include <linux/limits.h>
 
 #define __FORTIFY_INLINE extern __always_inline __gnu_inline __overloadable
 #define __RENAME(x) __asm__(#x)
@@ -17,9 +19,10 @@ void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("
 #define __compiletime_strlen(p)					\
 ({								\
 	unsigned char *__p = (unsigned char *)(p);		\
-	size_t __ret = (size_t)-1;				\
-	size_t __p_size = __builtin_object_size(p, 1);		\
-	if (__p_size != (size_t)-1) {				\
+	size_t __ret = SIZE_MAX;				\
+	size_t __p_size = __member_size(p);			\
+	if (__p_size != SIZE_MAX &&				\
+	    __builtin_constant_p(*__p)) {			\
 		size_t __p_len = __p_size - 1;			\
 		if (__builtin_constant_p(__p[__p_len]) &&	\
 		    __p[__p_len] == '\0')			\
@@ -69,20 +72,59 @@ extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size)
 	__underlying_memcpy(dst, src, bytes)
 
 /*
- * Clang's use of __builtin_object_size() within inlines needs hinting via
- * __pass_object_size(). The preference is to only ever use type 1 (member
+ * Clang's use of __builtin_*object_size() within inlines needs hinting via
+ * __pass_*object_size(). The preference is to only ever use type 1 (member
  * size, rather than struct size), but there remain some stragglers using
  * type 0 that will be converted in the future.
  */
-#define POS	__pass_object_size(1)
-#define POS0	__pass_object_size(0)
+#define POS			__pass_object_size(1)
+#define POS0			__pass_object_size(0)
+#define __struct_size(p)	__builtin_object_size(p, 0)
+#define __member_size(p)	__builtin_object_size(p, 1)
 
+#define __compiletime_lessthan(bounds, length)	(	\
+	__builtin_constant_p((bounds) < (length)) &&	\
+	(bounds) < (length)				\
+)
+
+/**
+ * strncpy - Copy a string to memory with non-guaranteed NUL padding
+ *
+ * @p: pointer to destination of copy
+ * @q: pointer to NUL-terminated source string to copy
+ * @size: bytes to write at @p
+ *
+ * If strlen(@q) >= @size, the copy of @q will stop after @size bytes,
+ * and @p will NOT be NUL-terminated
+ *
+ * If strlen(@q) < @size, following the copy of @q, trailing NUL bytes
+ * will be written to @p until @size total bytes have been written.
+ *
+ * Do not use this function. While FORTIFY_SOURCE tries to avoid
+ * over-reads of @q, it cannot defend against writing unterminated
+ * results to @p. Using strncpy() remains ambiguous and fragile.
+ * Instead, please choose an alternative, so that the expectation
+ * of @p's contents is unambiguous:
+ *
+ * +--------------------+-----------------+------------+
+ * | @p needs to be:    | padded to @size | not padded |
+ * +====================+=================+============+
+ * |     NUL-terminated | strscpy_pad()   | strscpy()  |
+ * +--------------------+-----------------+------------+
+ * | not NUL-terminated | strtomem_pad()  | strtomem() |
+ * +--------------------+-----------------+------------+
+ *
+ * Note strscpy*()'s differing return values for detecting truncation,
+ * and strtomem*()'s expectation that the destination is marked with
+ * __nonstring when it is a character array.
+ *
+ */
 __FORTIFY_INLINE __diagnose_as(__builtin_strncpy, 1, 2, 3)
 char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
 {
-	size_t p_size = __builtin_object_size(p, 1);
+	size_t p_size = __member_size(p);
 
-	if (__builtin_constant_p(size) && p_size < size)
+	if (__compiletime_lessthan(p_size, size))
 		__write_overflow();
 	if (p_size < size)
 		fortify_panic(__func__);
@@ -92,9 +134,9 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
 __FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2)
 char *strcat(char * const POS p, const char *q)
 {
-	size_t p_size = __builtin_object_size(p, 1);
+	size_t p_size = __member_size(p);
 
-	if (p_size == (size_t)-1)
+	if (p_size == SIZE_MAX)
 		return __underlying_strcat(p, q);
 	if (strlcat(p, q, p_size) >= p_size)
 		fortify_panic(__func__);
@@ -104,12 +146,12 @@ char *strcat(char * const POS p, const char *q)
 extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen);
 __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size_t maxlen)
 {
-	size_t p_size = __builtin_object_size(p, 1);
+	size_t p_size = __member_size(p);
 	size_t p_len = __compiletime_strlen(p);
 	size_t ret;
 
 	/* We can take compile-time actions when maxlen is const. */
-	if (__builtin_constant_p(maxlen) && p_len != (size_t)-1) {
+	if (__builtin_constant_p(maxlen) && p_len != SIZE_MAX) {
 		/* If p is const, we can use its compile-time-known len. */
 		if (maxlen >= p_size)
 			return p_len;
@@ -134,10 +176,10 @@ __FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1)
 __kernel_size_t __fortify_strlen(const char * const POS p)
 {
 	__kernel_size_t ret;
-	size_t p_size = __builtin_object_size(p, 1);
+	size_t p_size = __member_size(p);
 
 	/* Give up if we don't know how large p is. */
-	if (p_size == (size_t)-1)
+	if (p_size == SIZE_MAX)
 		return __underlying_strlen(p);
 	ret = strnlen(p, p_size);
 	if (p_size <= ret)
@@ -149,12 +191,12 @@ __kernel_size_t __fortify_strlen(const char * const POS p)
 extern size_t __real_strlcpy(char *, const char *, size_t) __RENAME(strlcpy);
 __FORTIFY_INLINE size_t strlcpy(char * const POS p, const char * const POS q, size_t size)
 {
-	size_t p_size = __builtin_object_size(p, 1);
-	size_t q_size = __builtin_object_size(q, 1);
+	size_t p_size = __member_size(p);
+	size_t q_size = __member_size(q);
 	size_t q_len;	/* Full count of source string length. */
 	size_t len;	/* Count of characters going into destination. */
 
-	if (p_size == (size_t)-1 && q_size == (size_t)-1)
+	if (p_size == SIZE_MAX && q_size == SIZE_MAX)
 		return __real_strlcpy(p, q, size);
 	q_len = strlen(q);
 	len = (q_len >= size) ? size - 1 : q_len;
@@ -178,18 +220,18 @@ __FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, s
 {
 	size_t len;
 	/* Use string size rather than possible enclosing struct size. */
-	size_t p_size = __builtin_object_size(p, 1);
-	size_t q_size = __builtin_object_size(q, 1);
+	size_t p_size = __member_size(p);
+	size_t q_size = __member_size(q);
 
 	/* If we cannot get size of p and q default to call strscpy. */
-	if (p_size == (size_t) -1 && q_size == (size_t) -1)
+	if (p_size == SIZE_MAX && q_size == SIZE_MAX)
 		return __real_strscpy(p, q, size);
 
 	/*
 	 * If size can be known at compile time and is greater than
 	 * p_size, generate a compile time write overflow error.
 	 */
-	if (__builtin_constant_p(size) && size > p_size)
+	if (__compiletime_lessthan(p_size, size))
 		__write_overflow();
 
 	/*
@@ -224,10 +266,10 @@ __FORTIFY_INLINE __diagnose_as(__builtin_strncat, 1, 2, 3)
 char *strncat(char * const POS p, const char * const POS q, __kernel_size_t count)
 {
 	size_t p_len, copy_len;
-	size_t p_size = __builtin_object_size(p, 1);
-	size_t q_size = __builtin_object_size(q, 1);
+	size_t p_size = __member_size(p);
+	size_t q_size = __member_size(q);
 
-	if (p_size == (size_t)-1 && q_size == (size_t)-1)
+	if (p_size == SIZE_MAX && q_size == SIZE_MAX)
 		return __underlying_strncat(p, q, count);
 	p_len = strlen(p);
 	copy_len = strnlen(q, count);
@@ -246,15 +288,16 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
 		/*
 		 * Length argument is a constant expression, so we
 		 * can perform compile-time bounds checking where
-		 * buffer sizes are known.
+		 * buffer sizes are also known at compile time.
 		 */
 
 		/* Error when size is larger than enclosing struct. */
-		if (p_size > p_size_field && p_size < size)
+		if (__compiletime_lessthan(p_size_field, p_size) &&
+		    __compiletime_lessthan(p_size, size))
 			__write_overflow();
 
 		/* Warn when write size is larger than dest field. */
-		if (p_size_field < size)
+		if (__compiletime_lessthan(p_size_field, size))
 			__write_overflow_field(p_size_field, size);
 	}
 	/*
@@ -268,10 +311,10 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
 	/*
 	 * Always stop accesses beyond the struct that contains the
 	 * field, when the buffer's remaining size is known.
-	 * (The -1 test is to optimize away checks where the buffer
+	 * (The SIZE_MAX test is to optimize away checks where the buffer
 	 * lengths are unknown.)
 	 */
-	if (p_size != (size_t)(-1) && p_size < size)
+	if (p_size != SIZE_MAX && p_size < size)
 		fortify_panic("memset");
 }
 
@@ -282,11 +325,11 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
 })
 
 /*
- * __builtin_object_size() must be captured here to avoid evaluating argument
- * side-effects further into the macro layers.
+ * __struct_size() vs __member_size() must be captured here to avoid
+ * evaluating argument side-effects further into the macro layers.
  */
 #define memset(p, c, s) __fortify_memset_chk(p, c, s,			\
-		__builtin_object_size(p, 0), __builtin_object_size(p, 1))
+		__struct_size(p), __member_size(p))
 
 /*
  * To make sure the compiler can enforce protection against buffer overflows,
@@ -319,7 +362,7 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
  * V = vulnerable to run-time overflow (will need refactoring to solve)
  *
  */
-__FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size,
+__FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
 					 const size_t p_size,
 					 const size_t q_size,
 					 const size_t p_size_field,
@@ -330,25 +373,28 @@ __FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size,
 		/*
 		 * Length argument is a constant expression, so we
 		 * can perform compile-time bounds checking where
-		 * buffer sizes are known.
+		 * buffer sizes are also known at compile time.
 		 */
 
 		/* Error when size is larger than enclosing struct. */
-		if (p_size > p_size_field && p_size < size)
+		if (__compiletime_lessthan(p_size_field, p_size) &&
+		    __compiletime_lessthan(p_size, size))
 			__write_overflow();
-		if (q_size > q_size_field && q_size < size)
+		if (__compiletime_lessthan(q_size_field, q_size) &&
+		    __compiletime_lessthan(q_size, size))
 			__read_overflow2();
 
 		/* Warn when write size argument larger than dest field. */
-		if (p_size_field < size)
+		if (__compiletime_lessthan(p_size_field, size))
 			__write_overflow_field(p_size_field, size);
 		/*
 		 * Warn for source field over-read when building with W=1
 		 * or when an over-write happened, so both can be fixed at
 		 * the same time.
 		 */
-		if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || p_size_field < size) &&
-		    q_size_field < size)
+		if ((IS_ENABLED(KBUILD_EXTRA_WARN1) ||
+		     __compiletime_lessthan(p_size_field, size)) &&
+		    __compiletime_lessthan(q_size_field, size))
 			__read_overflow2_field(q_size_field, size);
 	}
 	/*
@@ -362,41 +408,104 @@ __FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size,
 	/*
 	 * Always stop accesses beyond the struct that contains the
 	 * field, when the buffer's remaining size is known.
-	 * (The -1 test is to optimize away checks where the buffer
+	 * (The SIZE_MAX test is to optimize away checks where the buffer
 	 * lengths are unknown.)
 	 */
-	if ((p_size != (size_t)(-1) && p_size < size) ||
-	    (q_size != (size_t)(-1) && q_size < size))
+	if ((p_size != SIZE_MAX && p_size < size) ||
+	    (q_size != SIZE_MAX && q_size < size))
 		fortify_panic(func);
+
+	/*
+	 * Warn when writing beyond destination field size.
+	 *
+	 * We must ignore p_size_field == 0 for existing 0-element
+	 * fake flexible arrays, until they are all converted to
+	 * proper flexible arrays.
+	 *
+	 * The implementation of __builtin_*object_size() behaves
+	 * like sizeof() when not directly referencing a flexible
+	 * array member, which means there will be many bounds checks
+	 * that will appear at run-time, without a way for them to be
+	 * detected at compile-time (as can be done when the destination
+	 * is specifically the flexible array member).
+	 * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101832
+	 */
+	if (p_size_field != 0 && p_size_field != SIZE_MAX &&
+	    p_size != p_size_field && p_size_field < size)
+		return true;
+
+	return false;
 }
 
 #define __fortify_memcpy_chk(p, q, size, p_size, q_size,		\
 			     p_size_field, q_size_field, op) ({		\
 	size_t __fortify_size = (size_t)(size);				\
-	fortify_memcpy_chk(__fortify_size, p_size, q_size,		\
-			   p_size_field, q_size_field, #op);		\
+	WARN_ONCE(fortify_memcpy_chk(__fortify_size, p_size, q_size,	\
+				     p_size_field, q_size_field, #op),	\
+		  #op ": detected field-spanning write (size %zu) of single %s (size %zu)\n", \
+		  __fortify_size,					\
+		  "field \"" #p "\" at " __FILE__ ":" __stringify(__LINE__), \
+		  p_size_field);					\
 	__underlying_##op(p, q, __fortify_size);			\
 })
 
 /*
- * __builtin_object_size() must be captured here to avoid evaluating argument
- * side-effects further into the macro layers.
+ * Notes about compile-time buffer size detection:
+ *
+ * With these types...
+ *
+ *	struct middle {
+ *		u16 a;
+ *		u8 middle_buf[16];
+ *		int b;
+ *	};
+ *	struct end {
+ *		u16 a;
+ *		u8 end_buf[16];
+ *	};
+ *	struct flex {
+ *		int a;
+ *		u8 flex_buf[];
+ *	};
+ *
+ *	void func(TYPE *ptr) { ... }
+ *
+ * Cases where destination size cannot be currently detected:
+ * - the size of ptr's object (seemingly by design, gcc & clang fail):
+ *	__builtin_object_size(ptr, 1) == SIZE_MAX
+ * - the size of flexible arrays in ptr's obj (by design, dynamic size):
+ *	__builtin_object_size(ptr->flex_buf, 1) == SIZE_MAX
+ * - the size of ANY array at the end of ptr's obj (gcc and clang bug):
+ *	__builtin_object_size(ptr->end_buf, 1) == SIZE_MAX
+ *	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836
+ *
+ * Cases where destination size is currently detected:
+ * - the size of non-array members within ptr's object:
+ *	__builtin_object_size(ptr->a, 1) == 2
+ * - the size of non-flexible-array in the middle of ptr's obj:
+ *	__builtin_object_size(ptr->middle_buf, 1) == 16
+ *
+ */
+
+/*
+ * __struct_size() vs __member_size() must be captured here to avoid
+ * evaluating argument side-effects further into the macro layers.
  */
 #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,			\
-		__builtin_object_size(p, 0), __builtin_object_size(q, 0), \
-		__builtin_object_size(p, 1), __builtin_object_size(q, 1), \
+		__struct_size(p), __struct_size(q),			\
+		__member_size(p), __member_size(q),			\
 		memcpy)
 #define memmove(p, q, s)  __fortify_memcpy_chk(p, q, s,			\
-		__builtin_object_size(p, 0), __builtin_object_size(q, 0), \
-		__builtin_object_size(p, 1), __builtin_object_size(q, 1), \
+		__struct_size(p), __struct_size(q),			\
+		__member_size(p), __member_size(q),			\
 		memmove)
 
 extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan);
 __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
 {
-	size_t p_size = __builtin_object_size(p, 0);
+	size_t p_size = __struct_size(p);
 
-	if (__builtin_constant_p(size) && p_size < size)
+	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
 		fortify_panic(__func__);
@@ -406,13 +515,13 @@ __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
 __FORTIFY_INLINE __diagnose_as(__builtin_memcmp, 1, 2, 3)
 int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t size)
 {
-	size_t p_size = __builtin_object_size(p, 0);
-	size_t q_size = __builtin_object_size(q, 0);
+	size_t p_size = __struct_size(p);
+	size_t q_size = __struct_size(q);
 
 	if (__builtin_constant_p(size)) {
-		if (p_size < size)
+		if (__compiletime_lessthan(p_size, size))
 			__read_overflow();
-		if (q_size < size)
+		if (__compiletime_lessthan(q_size, size))
 			__read_overflow2();
 	}
 	if (p_size < size || q_size < size)
@@ -423,9 +532,9 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t
 __FORTIFY_INLINE __diagnose_as(__builtin_memchr, 1, 2, 3)
 void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
 {
-	size_t p_size = __builtin_object_size(p, 0);
+	size_t p_size = __struct_size(p);
 
-	if (__builtin_constant_p(size) && p_size < size)
+	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
 		fortify_panic(__func__);
@@ -435,9 +544,9 @@ void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
 void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv);
 __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size)
 {
-	size_t p_size = __builtin_object_size(p, 0);
+	size_t p_size = __struct_size(p);
 
-	if (__builtin_constant_p(size) && p_size < size)
+	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
 		fortify_panic(__func__);
@@ -447,9 +556,9 @@ __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size)
 extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup);
 __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp)
 {
-	size_t p_size = __builtin_object_size(p, 0);
+	size_t p_size = __struct_size(p);
 
-	if (__builtin_constant_p(size) && p_size < size)
+	if (__compiletime_lessthan(p_size, size))
 		__read_overflow();
 	if (p_size < size)
 		fortify_panic(__func__);
@@ -460,16 +569,18 @@ __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp
 __FORTIFY_INLINE __diagnose_as(__builtin_strcpy, 1, 2)
 char *strcpy(char * const POS p, const char * const POS q)
 {
-	size_t p_size = __builtin_object_size(p, 1);
-	size_t q_size = __builtin_object_size(q, 1);
+	size_t p_size = __member_size(p);
+	size_t q_size = __member_size(q);
 	size_t size;
 
 	/* If neither buffer size is known, immediately give up. */
-	if (p_size == (size_t)-1 && q_size == (size_t)-1)
+	if (__builtin_constant_p(p_size) &&
+	    __builtin_constant_p(q_size) &&
+	    p_size == SIZE_MAX && q_size == SIZE_MAX)
 		return __underlying_strcpy(p, q);
 	size = strlen(q) + 1;
 	/* Compile-time check for const size overflow. */
-	if (__builtin_constant_p(size) && p_size < size)
+	if (__compiletime_lessthan(p_size, size))
 		__write_overflow();
 	/* Run-time check for dynamic size overflow. */
 	if (p_size < size)