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>

2 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
index 450fa597c94d..a3aef5d55dba 100644
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -37,3 +37,5 @@
 #define __cold                  __attribute__((__cold__))
 
 #endif
+
+#define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 04fb5135b4e1..8e54108688f9 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -266,6 +266,10 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
 # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
 #endif
 
+/* Compile time object size, -1 for unknown */
+#ifndef __compiletime_object_size
+# define __compiletime_object_size(obj) -1
+#endif
 /*
  * Prevent the compiler from merging or refetching accesses.  The compiler
  * is also forbidden from reordering successive instances of ACCESS_ONCE(),