Hi Kees, On Wed, Dec 06, 2017 at 11:56:50AM -0800, Kees Cook wrote: > On Tue, Oct 31, 2017 at 8:51 AM, Dave Martin <Dave.Martin@xxxxxxx> wrote: > > Miscellaneous: > > > > * Change inconsistent copy_to_user() calls to __copy_to_user() in > > preserve_sve_context(). > > > > There are already __put_user_error() calls here. > > > > The whole extended signal frame is already checked for > > access_ok(VERIFY_WRITE) in get_sigframe(). > > Verifying all these __copy_to/from_user() calls is rather non-trivial. > For example, I had to understand that the access_ok() check actually > spans memory that both user->sigframe and user->next_frame point into. I don't think that's particularly difficult -- you just have to read the four lines preceding the access_ok. > And it isn't clear to me that all users of apply_user_offset() are > within this range too, along with other manually calculated offsets in > setup_sigframe(). The offsets passed into apply_user_offset are calculated by setup_sigframe_layout as the stack is allocated, so they're correct by construction. We could add a size check in apply_user_offset if you like? > And it's not clear if parse_user_sigframe() is safe either. Are > user->fpsimd and user->sve checked somewhere? It seems like it's > safely contained by in sf->uc.uc_mcontext.__reserved, but it's hard to > read, though I do see access_ok() checks against __reserved at the end > of the while loop. This one is certainly more difficult to follow, mainly because it's spread about a bit and we have to check the extra context separately. However, the main part of the frame is checked in sys_rt_sigreturn before calling restore_sigframe, and the extra context is checked in parse_user_sigframe if we find it. Dave, any thoughts on making this easier to understand? Will
