On Thu, Aug 27, 2020 at 06:26:11AM -0700, H.J. Lu wrote: > On Wed, Aug 26, 2020 at 12:57 PM Dave Hansen <dave.hansen@xxxxxxxxx> wrote: > > > > On 8/26/20 11:49 AM, Yu, Yu-cheng wrote: > > >> I would expect things like Go and various JITs to call it directly. > > >> > > >> If we wanted to be fancy and add a potentially more widely useful > > >> syscall, how about: > > >> > > >> mmap_special(void *addr, size_t length, int prot, int flags, int type); > > >> > > >> Where type is something like MMAP_SPECIAL_X86_SHSTK. Fundamentally, > > >> this is really just mmap() except that we want to map something a bit > > >> magical, and we don't want to require opening a device node to do it. > > > > > > One benefit of MMAP_SPECIAL_* is there are more free bits than MAP_*. > > > Does ARM have similar needs for memory mapping, Dave? > > > > No idea. > > > > But, mmap_special() is *basically* mmap2() with extra-big flags space. > > I suspect it will grow some more uses on top of shadow stacks. It could > > have, for instance, been used to allocate MPX bounds tables. > > There is no reason we can't use > > long arch_prctl (int, unsigned long, unsigned long, unsigned long, ..); > > for ARCH_X86_CET_MMAP_SHSTK. We just need to use > > syscall (SYS_arch_prctl, ARCH_X86_CET_MMAP_SHSTK, ...); For arm64 (and sparc etc.) we continue to use the regular mmap/mprotect family of calls. One or two additional arch-specific mmap flags are sufficient for now. Is x86 definitely not going to fit within those calls? For now, I can't see what arg[2] is used for (and hence the type argument of mmap_special()), but I haven't dug through the whole series. Cheers ---Dave
