linux-kernel - Re: [PATCH 1/4] task_struct: Allow randomized layout

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Message-ID: <20180326120321.GD4129@hirez.programming.kicks-ass.net>
Date:   Mon, 26 Mar 2018 14:03:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     kernel-hardening@...ts.openwall.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/4] task_struct: Allow randomized layout

On Mon, Mar 26, 2018 at 01:52:46PM +0200, Peter Zijlstra wrote:

> That now looks like:
> 
> struct task_struct {
>         struct thread_info         thread_info;          /*     0    16 */
>         volatile long int          state;                /*    16     8 */
> 
>         /* XXX 40 bytes hole, try to pack */
> 
>         /* --- cacheline 1 boundary (64 bytes) --- */
>         struct {
>                 void *             stack;                /*    64     8 */
>                 atomic_t           usage;                /*    72     4 */
>                 unsigned int       flags;                /*    76     4 */
>                 unsigned int       ptrace;               /*    80     4 */
>                 struct llist_node  wake_entry;           /*    88     8 */
> 
> 
> Can we please undo this crap?

The below gets rid of that nonsense.

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index e2c7f4369eff..767cf74d61f7 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -242,6 +242,15 @@
 #if defined(RANDSTRUCT_PLUGIN) && !defined(__CHECKER__)
 #define __randomize_layout __attribute__((randomize_layout))
 #define __no_randomize_layout __attribute__((no_randomize_layout))
+/*
+ * 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
 
 #endif /* GCC_VERSION >= 40500 */
@@ -256,15 +265,6 @@
  */
 #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 */