+ task_struct-only-use-anon-struct-under-randstruct-plugin.patch added to -mm tree

The patch titled
     Subject: task_struct: only use anon struct under randstruct plugin
has been added to the -mm tree.  Its filename is
     task_struct-only-use-anon-struct-under-randstruct-plugin.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/task_struct-only-use-anon-struct-under-randstruct-plugin.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/task_struct-only-use-anon-struct-under-randstruct-plugin.patch

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------------------------------------------------------
From: Kees Cook <redacted>
Subject: task_struct: only use anon struct under randstruct plugin

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 <redacted>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/compiler-clang.h |    3 ---
 include/linux/compiler-gcc.h   |   12 +++---------
 2 files changed, 3 insertions(+), 12 deletions(-)

diff -puN include/linux/compiler-clang.h~task_struct-only-use-anon-struct-under-randstruct-plugin include/linux/compiler-clang.h

--- a/include/linux/compiler-clang.h~task_struct-only-use-anon-struct-under-randstruct-plugin
+++ a/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	};
-
 /* all clang versions usable with the kernel support KASAN ABI version 5 */
 #define KASAN_ABI_VERSION 5
 

diff -puN include/linux/compiler-gcc.h~task_struct-only-use-anon-struct-under-randstruct-plugin include/linux/compiler-gcc.h

--- a/include/linux/compiler-gcc.h~task_struct-only-use-anon-struct-under-randstruct-plugin
+++ a/include/linux/compiler-gcc.h

@@ -242,6 +242,9 @@
 #if defined(RANDSTRUCT_PLUGIN) && !defined(__CHECKER__)
 #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 */

@@ -256,15 +259,6 @@
  */
 #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 */
 
 

_

Patches currently in -mm which might be from keescook@chromium.org are

taint-convert-to-indexed-initialization.patch
taint-consolidate-documentation.patch
taint-add-taint-for-randstruct.patch
kernelh-introduce-const_max-for-vla-removal.patch
remove-false-positive-vlas-when-using-max.patch
task_struct-only-use-anon-struct-under-randstruct-plugin.patch
test_bitmap-do-not-accidentally-use-stack-vla.patch
fork-unconditionally-clear-stack-on-fork.patch
exec-pass-stack-rlimit-into-mm-layout-functions.patch
exec-introduce-finalize_exec-before-start_thread.patch
exec-pin-stack-limit-during-exec.patch
exofs-avoid-vla-in-structures.patch