4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kees Cook <keescook@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> Reported-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/linux/compiler-clang.h | 3 --- include/linux/compiler-gcc.h | 12 +++--------- 2 files changed, 3 insertions(+), 12 deletions(-) --- 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 --- 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 */