4.14-stable review patch. If anyone has any objections, please let me know.
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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 };