x86: Use __builtin_object_size() to validate the buffer size for copy_from_user()

gcc (4.x) supports the __builtin_object_size() builtin, which
reports the size of an object that a pointer point to, when known
at compile time. If the buffer size is not known at compile time, a
constant -1 is returned.

This patch uses this feature to add a sanity check to
copy_from_user(); if the target buffer is known to be smaller than
the copy size, the copy is aborted and a WARNing is emitted in
memory debug mode.

These extra checks compile away when the object size is not known,
or if both the buffer size and the copy length are constants.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
LKML-Reference: <20090926143301.2c396b94@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 18 insertions, 1 deletions

diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h
index 632fb44b4cb..582d6aef741 100644
--- a/arch/x86/include/asm/uaccess_32.h
+++ b/arch/x86/include/asm/uaccess_32.h
@@ -187,9 +187,26 @@ __copy_from_user_inatomic_nocache(void *to, const void __user *from,
 
 unsigned long __must_check copy_to_user(void __user *to,
 					const void *from, unsigned long n);
-unsigned long __must_check copy_from_user(void *to,
+unsigned long __must_check _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)
+{
+	int sz = __compiletime_object_size(to);
+	int ret = -EFAULT;
+
+	if (likely(sz == -1 || sz >= n))
+		ret = _copy_from_user(to, from, n);
+#ifdef CONFIG_DEBUG_VM
+	else
+		WARN(1, "Buffer overflow detected!\n");
+#endif
+	return ret;
+}
+
 long __must_check strncpy_from_user(char *dst, const char __user *src,
 				    long count);
 long __must_check __strncpy_from_user(char *dst,