Messages in this thread | | | Date | Mon, 4 Dec 2017 13:08:08 +0100 | From | Greg KH <> | Subject | Re: [PATCH] compiler, clang: handle randomizable anonymous structs |
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On Fri, Dec 01, 2017 at 06:18:08PM -0800, Alexei Starovoitov wrote: > On Thu, Nov 09, 2017 at 12:16:45PM +0530, Sandipan Das wrote: > > 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. > > > > Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com> > > --- > > include/linux/compiler-clang.h | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h > > index 54dfef70a072..780b1242bf24 100644 > > --- 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 }; > > -- > > 2.13.6 > > Andrew or Greg, > could you please pull this patch into 4.13 and 4.14 releases as well ? > Sorry we missed the stable tag when submitting it originally. > It is commit 4ca59b14e588 ("include/linux/compiler-clang.h: handle randomizable anonymous structs")
4.13 is end-of-life, but 4.14 is not, so I've queued it up for that one.
thanks,
greg k-h
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