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task_struct: only use anon struct under randstruct plugin

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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: 29e48ce87f ("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>
This commit is contained in:
Kees Cook 2018-04-10 16:32:44 -07:00 committed by Linus Torvalds
parent d4ef8d3ff0
commit 2cfe0d3009
2 changed files with 3 additions and 12 deletions
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3
include/linux/compiler-clang.h
View File

@ -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

12
include/linux/compiler-gcc.h
View File

@ -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 */