On Wed, Mar 29, 2017 at 1:45 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote: > On 03/29/17 13:39, Kees Cook wrote: >> This removes ARCH_WANTS_DYNAMIC_TASK_STRUCT from x86, leaving only s390 >> still defining this config. >> >> In order to support future structure layout randomization of the >> task_struct, none of the structure fields are allowed to have a specific >> position or dynamic size. To enable randomization of task_struct on >> x86, the FPU state must be moved to its own dynamically sized cache, >> and dereferenced from the task_struct. >> >> This change is nearly identical to what was done in grsecurity to support >> structure layout randomization. Hopefully I found all the needed changes. >> This passes allyesconfig, and boot tests. > > Is this really what we want to happen? It seems much more sane to > simply make them adjacent; they don't need to be part of the same > structure (in practice, there are three objects: thread_info, > task_struct, and the FPU state.) They're adjacent already, which poses a problem for the struct layout randomization plugin, since adjacency may no longer be true (after layout randomization). This adjacency (or not) isn't really the problem: it's that FPU state size is only known at runtime. Another solution would be to have FPU state be a fixed size... -Kees -- Kees Cook Pixel Security
