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Lu" Date: Thu, 27 Aug 2020 06:26:11 -0700 Message-ID: Subject: Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack To: Dave Hansen Cc: "Yu, Yu-cheng" , Andy Lutomirski , Florian Weimer , Dave Martin , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , LKML , "open list:DOCUMENTATION" , Linux-MM , linux-arch , Linux API , Arnd Bergmann , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Weijiang Yang Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 033C51AD1B3 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Aug 26, 2020 at 12:57 PM Dave Hansen 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, ...); -- H.J.