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* [PATCH] task_struct: Only use anon struct under randstruct plugin
@ 2018-03-27 21:36 Kees Cook
  2018-03-27 23:03 ` Andrew Morton
  0 siblings, 1 reply; 6+ messages in thread
From: Kees Cook @ 2018-03-27 21:36 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Peter Zijlstra, Ingo Molnar, Linus Torvalds, linux-kernel,
	kernel-hardening

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.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Fixes: 29e48ce87f1e ("task_struct: Allow randomized")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/linux/compiler-clang.h |  3 ---
 include/linux/compiler-gcc.h   | 12 +++---------
 2 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index d3f264a5b04d..ceb96ecab96e 100644
--- 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	};
-
 /* all clang versions usable with the kernel support KASAN ABI version 5 */
 #define KASAN_ABI_VERSION 5
 
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index e2c7f4369eff..b4bf73f5e38f 100644
--- a/include/linux/compiler-gcc.h
+++ b/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 */
 
 
-- 
2.7.4


-- 
Kees Cook
Pixel Security

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2018-03-28  9:51 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-03-27 21:36 [PATCH] task_struct: Only use anon struct under randstruct plugin Kees Cook
2018-03-27 23:03 ` Andrew Morton
2018-03-28  0:22   ` Linus Torvalds
2018-03-28  9:51     ` Peter Zijlstra
2018-03-28  0:30   ` Kees Cook
2018-03-28  1:34     ` Andrew Morton

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