From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [195.92.253.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 408g8m6DN3zF1xB for ; Mon, 26 Mar 2018 14:48:08 +1100 (AEDT) Date: Mon, 26 Mar 2018 04:47:50 +0100 From: Al Viro To: Ingo Molnar Cc: Linus Torvalds , Dominik Brodowski , Linux Kernel Mailing List , Arnd Bergmann , linux-arch , Ralf Baechle , James Hogan , linux-mips , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , ppc-dev , Martin Schwidefsky , Heiko Carstens , linux-s390 , "David S . Miller" , sparclinux@vger.kernel.org, Ingo Molnar , Jiri Slaby , the arch/x86 maintainers Subject: Re: [RFC] new SYSCALL_DEFINE/COMPAT_SYSCALL_DEFINE wrappers Message-ID: <20180326034750.GN30522@ZenIV.linux.org.uk> References: <20180318161056.5377-1-linux@dominikbrodowski.net> <20180318161056.5377-5-linux@dominikbrodowski.net> <20180318174014.GR30522@ZenIV.linux.org.uk> <20180318181848.GU30522@ZenIV.linux.org.uk> <20180319042300.GW30522@ZenIV.linux.org.uk> <20180319092920.tbh2xwkruegshzqe@gmail.com> <20180319232342.GX30522@ZenIV.linux.org.uk> <20180322001532.GA18399@ZenIV.linux.org.uk> <20180326004017.GA2211@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20180326004017.GA2211@ZenIV.linux.org.uk> Sender: Al Viro List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Mar 26, 2018 at 01:40:17AM +0100, Al Viro wrote: > Kinda-sorta part: > * asmlinkage_protect is taken out for now, so m68k has problems. > * syscalls that run out of 6 slots barf violently. For mips it's > wrong (there we have 8 slots); for stuff like arm and ppc it's right, but > it means that things like e.g. compat sync_file_range() should not even > be compiled on those. __ARCH_WANT_SYS_SYNC_FILE_RANGE, presumably... > In any case, we *can't* do pt_regs-based wrappers for those syscalls on > such architectures, so ifdefs around those puppies are probably the right > thing to do. > * s390 macrology in compat_wrapper.c not even touched; it needs > a trivial update to keep working (__MAP callbacks take an extra argument, > unused for those users). > * sys_... and compat_sys_... aliases are unchanged; if we kill > direct callers, we can trivially rename SyS##name and compat_SyS##name > to sys##name and compat_sys##name and get rid of aliases. * mips n32 and x86 x32 can become an extra source of headache. That actually applies to any plans of passing struct pt_regs *. As it is, e.g. syscall 515 on amd64 is compat_sys_readv(). Dispatched via this: /* * NB: Native and x32 syscalls are dispatched from the same * table. The only functional difference is the x32 bit in * regs->orig_ax, which changes the behavior of some syscalls. */ if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) { nr = array_index_nospec(nr & __SYSCALL_MASK, NR_syscalls); regs->ax = sys_call_table[nr]( regs->di, regs->si, regs->dx, regs->r10, regs->r8, regs->r9); } Now, syscall 145 via 32bit call is *also* compat_sys_readv(), dispatched via nr = array_index_nospec(nr, IA32_NR_syscalls); /* * It's possible that a 32-bit syscall implementation * takes a 64-bit parameter but nonetheless assumes that * the high bits are zero. Make sure we zero-extend all * of the args. */ regs->ax = ia32_sys_call_table[nr]( (unsigned int)regs->bx, (unsigned int)regs->cx, (unsigned int)regs->dx, (unsigned int)regs->si, (unsigned int)regs->di, (unsigned int)regs->bp); Right now it works - we call the same function, passing it arguments picked from different set of registers (di/si/dx in x32 case, bx/cx/dx in i386 one). But if we switch to passing struct pt_regs * and have the wrapper fetch regs->{bx,cx,dx}, we have a problem. It won't work for both entry points. IMO it's a good reason to have dispatcher(s) handle extraction from pt_regs and let the wrapper deal with the resulting 6 u64 or 6 u32, normalizing them and arranging them into arguments expected by syscall body. Linus, Dominik - how do you plan dealing with that fun? Regardless of the way we generate the glue, the issue remains. We can't get the same struct pt_regs *-taking function for both; we either need to produce a separate chunk of glue for each compat_sys_... involved (either making COMPAT_SYSCALL_DEFINE generate both, or having duplicate X32_SYSCALL_DEFINE for each of those COMPAT_SYSCALL_DEFINE - with identical body, at that) or we need to have the registers-to-slots mapping done in dispatcher...