- Inlines copy_*_user() for correct use of __builtin_const_p() for hardened

usercopy and the recent compile-time checks.
 - Switches hardened usercopy to only check non-const size arguments to avoid
   meaningless checks on likely-sane const values.
 - Updates lkdtm usercopy tests to compenstate for the const checking.
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v1
 Comment: Kees Cook <kees@outflux.net>
 
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 IPxwxvEYGHcgmKeFlrjhssOqw1hs0q8D4DVRnlu1NV4XF4b9b+Jz3Tf7PoOhgLLR
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 ACqYh+dcH2v/2DNxigcH
 =bFFM
 -----END PGP SIGNATURE-----

Merge tag 'usercopy-v4.8-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull hardened usercopy fixes from Kees Cook:

 - inline copy_*_user() for correct use of __builtin_const_p() for
   hardened usercopy and the recent compile-time checks.

 - switch hardened usercopy to only check non-const size arguments to
   avoid meaningless checks on likely-sane const values.

 - update lkdtm usercopy tests to compenstate for the const checking.

* tag 'usercopy-v4.8-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  lkdtm: adjust usercopy tests to bypass const checks
  usercopy: fold builtin_const check into inline function
  x86/uaccess: force copy_*_user() to be inlined

arch/ia64/include/asm/uaccess.h

@@ -241,8 +241,7 @@ extern unsigned long __must_check __copy_user (void __user *to, const void __use
 static inline unsigned long
 __copy_to_user (void __user *to, const void *from, unsigned long count)
 {
-	if (!__builtin_constant_p(count))
-		check_object_size(from, count, true);
+	check_object_size(from, count, true);
 
 	return __copy_user(to, (__force void __user *) from, count);
 }
@@ -250,8 +249,7 @@ __copy_to_user (void __user *to, const void *from, unsigned long count)
 static inline unsigned long
 __copy_from_user (void *to, const void __user *from, unsigned long count)
 {
-	if (!__builtin_constant_p(count))
-		check_object_size(to, count, false);
+	check_object_size(to, count, false);
 
 	return __copy_user((__force void __user *) to, from, count);
 }
@@ -265,8 +263,7 @@ __copy_from_user (void *to, const void __user *from, unsigned long count)
 	long __cu_len = (n);								\
 											\
 	if (__access_ok(__cu_to, __cu_len, get_fs())) {					\
-		if (!__builtin_constant_p(n))						\
-			check_object_size(__cu_from, __cu_len, true);			\
+		check_object_size(__cu_from, __cu_len, true);			\
 		__cu_len = __copy_user(__cu_to, (__force void __user *)  __cu_from, __cu_len);	\
 	}										\
 	__cu_len;									\
@@ -280,8 +277,7 @@ __copy_from_user (void *to, const void __user *from, unsigned long count)
 											\
 	__chk_user_ptr(__cu_from);							\
 	if (__access_ok(__cu_from, __cu_len, get_fs())) {				\
-		if (!__builtin_constant_p(n))						\
-			check_object_size(__cu_to, __cu_len, false);			\
+		check_object_size(__cu_to, __cu_len, false);			\
 		__cu_len = __copy_user((__force void __user *) __cu_to, __cu_from, __cu_len);	\
 	}										\
 	__cu_len;									\

arch/powerpc/include/asm/uaccess.h

@@ -311,14 +311,12 @@ static inline unsigned long copy_from_user(void *to,
 	unsigned long over;
 
 	if (access_ok(VERIFY_READ, from, n)) {
-		if (!__builtin_constant_p(n))
-			check_object_size(to, n, false);
+		check_object_size(to, n, false);
 		return __copy_tofrom_user((__force void __user *)to, from, n);
 	}
 	if ((unsigned long)from < TASK_SIZE) {
 		over = (unsigned long)from + n - TASK_SIZE;
-		if (!__builtin_constant_p(n - over))
-			check_object_size(to, n - over, false);
+		check_object_size(to, n - over, false);
 		return __copy_tofrom_user((__force void __user *)to, from,
 				n - over) + over;
 	}
@@ -331,14 +329,12 @@ static inline unsigned long copy_to_user(void __user *to,
 	unsigned long over;
 
 	if (access_ok(VERIFY_WRITE, to, n)) {
-		if (!__builtin_constant_p(n))
-			check_object_size(from, n, true);
+		check_object_size(from, n, true);
 		return __copy_tofrom_user(to, (__force void __user *)from, n);
 	}
 	if ((unsigned long)to < TASK_SIZE) {
 		over = (unsigned long)to + n - TASK_SIZE;
-		if (!__builtin_constant_p(n))
-			check_object_size(from, n - over, true);
+		check_object_size(from, n - over, true);
 		return __copy_tofrom_user(to, (__force void __user *)from,
 				n - over) + over;
 	}
@@ -383,8 +379,7 @@ static inline unsigned long __copy_from_user_inatomic(void *to,
 			return 0;
 	}
 
-	if (!__builtin_constant_p(n))
-		check_object_size(to, n, false);
+	check_object_size(to, n, false);
 
 	return __copy_tofrom_user((__force void __user *)to, from, n);
 }
@@ -412,8 +407,8 @@ static inline unsigned long __copy_to_user_inatomic(void __user *to,
 		if (ret == 0)
 			return 0;
 	}
-	if (!__builtin_constant_p(n))
-		check_object_size(from, n, true);
+
+	check_object_size(from, n, true);
 
 	return __copy_tofrom_user(to, (__force const void __user *)from, n);
 }

arch/sparc/include/asm/uaccess_32.h

@@ -249,8 +249,7 @@ unsigned long __copy_user(void __user *to, const void __user *from, unsigned lon
 static inline unsigned long copy_to_user(void __user *to, const void *from, unsigned long n)
 {
 	if (n && __access_ok((unsigned long) to, n)) {
-		if (!__builtin_constant_p(n))
-			check_object_size(from, n, true);
+		check_object_size(from, n, true);
 		return __copy_user(to, (__force void __user *) from, n);
 	} else
 		return n;
@@ -258,16 +257,14 @@ static inline unsigned long copy_to_user(void __user *to, const void *from, unsi
 
 static inline unsigned long __copy_to_user(void __user *to, const void *from, unsigned long n)
 {
-	if (!__builtin_constant_p(n))
-		check_object_size(from, n, true);
+	check_object_size(from, n, true);
 	return __copy_user(to, (__force void __user *) from, n);
 }
 
 static inline unsigned long copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	if (n && __access_ok((unsigned long) from, n)) {
-		if (!__builtin_constant_p(n))
-			check_object_size(to, n, false);
+		check_object_size(to, n, false);
 		return __copy_user((__force void __user *) to, from, n);
 	} else
 		return n;

arch/sparc/include/asm/uaccess_64.h

@@ -212,8 +212,7 @@ copy_from_user(void *to, const void __user *from, unsigned long size)
 {
 	unsigned long ret;
 
-	if (!__builtin_constant_p(size))
-		check_object_size(to, size, false);
+	check_object_size(to, size, false);
 
 	ret = ___copy_from_user(to, from, size);
 	if (unlikely(ret))
@@ -233,8 +232,8 @@ copy_to_user(void __user *to, const void *from, unsigned long size)
 {
 	unsigned long ret;
 
-	if (!__builtin_constant_p(size))
-		check_object_size(from, size, true);
+	check_object_size(from, size, true);
+
 	ret = ___copy_to_user(to, from, size);
 	if (unlikely(ret))
 		ret = copy_to_user_fixup(to, from, size);

arch/x86/include/asm/uaccess.h

@@ -705,7 +705,7 @@ static inline void copy_user_overflow(int size, unsigned long count)
 	WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
 }
 
-static inline unsigned long __must_check
+static __always_inline unsigned long __must_check
 copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	int sz = __compiletime_object_size(to);
@@ -725,7 +725,7 @@ copy_from_user(void *to, const void __user *from, unsigned long n)
 	return n;
 }
 
-static inline unsigned long __must_check
+static __always_inline unsigned long __must_check
 copy_to_user(void __user *to, const void *from, unsigned long n)
 {
 	int sz = __compiletime_object_size(from);

drivers/misc/lkdtm_usercopy.c

@@ -9,7 +9,15 @@
 #include <linux/uaccess.h>
 #include <asm/cacheflush.h>
 
-static size_t cache_size = 1024;
+/*
+ * Many of the tests here end up using const sizes, but those would
+ * normally be ignored by hardened usercopy, so force the compiler
+ * into choosing the non-const path to make sure we trigger the
+ * hardened usercopy checks by added "unconst" to all the const copies,
+ * and making sure "cache_size" isn't optimized into a const.
+ */
+static volatile size_t unconst = 0;
+static volatile size_t cache_size = 1024;
 static struct kmem_cache *bad_cache;
 
 static const unsigned char test_text[] = "This is a test.\n";
@@ -67,14 +75,14 @@ static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
 	if (to_user) {
 		pr_info("attempting good copy_to_user of local stack\n");
 		if (copy_to_user((void __user *)user_addr, good_stack,
-				 sizeof(good_stack))) {
+				 unconst + sizeof(good_stack))) {
 			pr_warn("copy_to_user failed unexpectedly?!\n");
 			goto free_user;
 		}
 
 		pr_info("attempting bad copy_to_user of distant stack\n");
 		if (copy_to_user((void __user *)user_addr, bad_stack,
-				 sizeof(good_stack))) {
+				 unconst + sizeof(good_stack))) {
 			pr_warn("copy_to_user failed, but lacked Oops\n");
 			goto free_user;
 		}
@@ -88,14 +96,14 @@ static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
 
 		pr_info("attempting good copy_from_user of local stack\n");
 		if (copy_from_user(good_stack, (void __user *)user_addr,
-				   sizeof(good_stack))) {
+				   unconst + sizeof(good_stack))) {
 			pr_warn("copy_from_user failed unexpectedly?!\n");
 			goto free_user;
 		}
 
 		pr_info("attempting bad copy_from_user of distant stack\n");
 		if (copy_from_user(bad_stack, (void __user *)user_addr,
-				   sizeof(good_stack))) {
+				   unconst + sizeof(good_stack))) {
 			pr_warn("copy_from_user failed, but lacked Oops\n");
 			goto free_user;
 		}
@@ -109,7 +117,7 @@ static void do_usercopy_heap_size(bool to_user)
 {
 	unsigned long user_addr;
 	unsigned char *one, *two;
-	const size_t size = 1024;
+	size_t size = unconst + 1024;
 
 	one = kmalloc(size, GFP_KERNEL);
 	two = kmalloc(size, GFP_KERNEL);
@@ -285,13 +293,14 @@ void lkdtm_USERCOPY_KERNEL(void)
 
 	pr_info("attempting good copy_to_user from kernel rodata\n");
 	if (copy_to_user((void __user *)user_addr, test_text,
-			 sizeof(test_text))) {
+			 unconst + sizeof(test_text))) {
 		pr_warn("copy_to_user failed unexpectedly?!\n");
 		goto free_user;
 	}
 
 	pr_info("attempting bad copy_to_user from kernel text\n");
-	if (copy_to_user((void __user *)user_addr, vm_mmap, PAGE_SIZE)) {
+	if (copy_to_user((void __user *)user_addr, vm_mmap,
+			 unconst + PAGE_SIZE)) {
 		pr_warn("copy_to_user failed, but lacked Oops\n");
 		goto free_user;
 	}

include/linux/thread_info.h

@@ -121,7 +121,8 @@ extern void __check_object_size(const void *ptr, unsigned long n,
 static inline void check_object_size(const void *ptr, unsigned long n,
 				     bool to_user)
 {
-	__check_object_size(ptr, n, to_user);
+	if (!__builtin_constant_p(n))
+		__check_object_size(ptr, n, to_user);
 }
 #else
 static inline void check_object_size(const void *ptr, unsigned long n,