[S390] uaccess: implement strict user copy checks

Same as on x86 and sparc, besides the fact that enabling the option
will just emit compile time warnings instead of errors.
Keeps allyesconfig kernels compiling.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index cbf0a8745bf4..d6b1ed0ec52b 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -265,6 +265,12 @@ __copy_from_user(void *to, const void __user *from, unsigned long n)
 		return uaccess.copy_from_user(n, from, to);
 }
 
+extern void copy_from_user_overflow(void)
+#ifdef CONFIG_DEBUG_STRICT_USER_COPY_CHECKS
+__compiletime_warning("copy_from_user() buffer size is not provably correct")
+#endif
+;
+
 /**
  * copy_from_user: - Copy a block of data from user space.
  * @to:   Destination address, in kernel space.
@@ -284,7 +290,13 @@ __copy_from_user(void *to, const void __user *from, unsigned long n)
 static inline unsigned long __must_check
 copy_from_user(void *to, const void __user *from, unsigned long n)
 {
+	unsigned int sz = __compiletime_object_size(to);
+
 	might_fault();
+	if (unlikely(sz != -1 && sz < n)) {
+		copy_from_user_overflow();
+		return n;
+	}
 	if (access_ok(VERIFY_READ, from, n))
 		n = __copy_from_user(to, from, n);
 	else