Patch "include/linux/compiler-clang.h: handle randomizable anonymous structs" has been added to the 4.14-stable tree

Patch "include/linux/compiler-clang.h: handle randomizable anonymous structs" has been added to the 4.14-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    include/linux/compiler-clang.h: handle randomizable anonymous structs

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     include-linux-compiler-clang.h-handle-randomizable-anonymous-structs.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 4ca59b14e588f873795a11cdc77a25c686a29d23 Mon Sep 17 00:00:00 2001
From: Sandipan Das <sandipan@linux.vnet.ibm.com>
Date: Fri, 17 Nov 2017 15:27:28 -0800
Subject: include/linux/compiler-clang.h: handle randomizable anonymous structs

From: Sandipan Das <sandipan@linux.vnet.ibm.com>

commit 4ca59b14e588f873795a11cdc77a25c686a29d23 upstream.

The GCC randomize layout plugin can randomize the member offsets of
sensitive kernel data structures.  To use this feature, certain
annotations and members are added to the structures which affect the
member offsets even if this plugin is not used.

All of these structures are completely randomized, except for task_struct
which leaves out some of its members.  All the other members are wrapped
within an anonymous struct with the __randomize_layout attribute.  This is
done using the randomized_struct_fields_start and
randomized_struct_fields_end defines.

When the plugin is disabled, the behaviour of this attribute can vary
based on the GCC version.  For GCC 5.1+, this attribute maps to
__designated_init otherwise it is just an empty define but the anonymous
structure is still present.  For other compilers, both
randomized_struct_fields_start and randomized_struct_fields_end default
to empty defines meaning the anonymous structure is not introduced at
all.

So, if a module compiled with Clang, such as a BPF program, needs to
access task_struct fields such as pid and comm, the offsets of these
members as recognized by Clang are different from those recognized by
modules compiled with GCC.  If GCC 4.6+ is used to build the kernel,
this can be solved by introducing appropriate defines for Clang so that
the anonymous structure is seen when determining the offsets for the
members.

Link: http://lkml.kernel.org/r/20171109064645.25581-1-sandipan@linux.vnet.ibm.com
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Alexei Starovoitov <ast@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 include/linux/compiler-clang.h |    3 +++
 1 file changed, 3 insertions(+)

--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -16,3 +16,6 @@
  * with any version that can compile the kernel
  */
 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
+
+#define randomized_struct_fields_start	struct {
+#define randomized_struct_fields_end	};


Patches currently in stable-queue which might be from sandipan@linux.vnet.ibm.com are

queue-4.14/include-linux-compiler-clang.h-handle-randomizable-anonymous-structs.patch