task_struct: only use anon struct under randstruct plugin

commit 2cfe0d3009418a132b93d78642a8059a38fe5944 upstream.

The original intent for always adding the anonymous struct in
task_struct was to make sure we had compiler coverage.

However, this caused pathological padding of 40 bytes at the start of
task_struct.  Instead, move the anonymous struct to being only used when
struct layout randomization is enabled.

Link: http://lkml.kernel.org/r/20180327213609.GA2964@beast
Fixes: 29e48ce87f1e ("task_struct: Allow randomized")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index be3aef6839f610a2eca3ff468bafe2606e914365..070f85d92c15c1005b4fe76bdcc3d51453b2b477 100644 (file)
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -17,9 +17,6 @@
  */
 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
 
-#define randomized_struct_fields_start struct {
-#define randomized_struct_fields_end   };
-
 /* Clang doesn't have a way to turn it off per-function, yet. */
 #ifdef __noretpoline
 #undef __noretpoline

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index a1ffbf25873fd93a10863044a1981df772174918..b78b31af36f889c69823e12f6eee8ebca40fd770 100644 (file)
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -229,6 +229,9 @@
 #ifdef RANDSTRUCT_PLUGIN
 #define __randomize_layout __attribute__((randomize_layout))
 #define __no_randomize_layout __attribute__((no_randomize_layout))
+/* This anon struct can add padding, so only enable it under randstruct. */
+#define randomized_struct_fields_start struct {
+#define randomized_struct_fields_end   } __randomize_layout;
 #endif
 
 #endif /* GCC_VERSION >= 40500 */
@@ -243,15 +246,6 @@
  */
 #define __visible      __attribute__((externally_visible))
 
-/*
- * RANDSTRUCT_PLUGIN wants to use an anonymous struct, but it is only
- * possible since GCC 4.6. To provide as much build testing coverage
- * as possible, this is used for all GCC 4.6+ builds, and not just on
- * RANDSTRUCT_PLUGIN builds.
- */
-#define randomized_struct_fields_start struct {
-#define randomized_struct_fields_end   } __randomize_layout;
-
 #endif /* GCC_VERSION >= 40600 */