From: Kees Cook keescook@chromium.org 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 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 ---

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 */

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