From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3F2ACC49EA5 for ; Thu, 24 Jun 2021 22:45:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 23129613BD for ; Thu, 24 Jun 2021 22:45:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232856AbhFXWsQ (ORCPT ); Thu, 24 Jun 2021 18:48:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44354 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229521AbhFXWsN (ORCPT ); Thu, 24 Jun 2021 18:48:13 -0400 Received: from zeniv-ca.linux.org.uk (zeniv-ca.linux.org.uk [IPv6:2607:5300:60:148a::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E0809C061574; Thu, 24 Jun 2021 15:45:53 -0700 (PDT) Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1lwY67-00BwuB-I0; Thu, 24 Jun 2021 22:45:23 +0000 Date: Thu, 24 Jun 2021 22:45:23 +0000 From: Al Viro To: "Eric W. Biederman" Cc: Linus Torvalds , Michael Schmitz , linux-arch , Jens Axboe , Oleg Nesterov , Linux Kernel Mailing List , Richard Henderson , Ivan Kokshaysky , Matt Turner , alpha , Geert Uytterhoeven , linux-m68k , Arnd Bergmann , Ley Foon Tan , Tejun Heo , Kees Cook Subject: Re: [PATCH 0/9] Refactoring exit Message-ID: References: <87a6njf0ia.fsf@disp2133> <87tulpbp19.fsf@disp2133> <87zgvgabw1.fsf@disp2133> <875yy3850g.fsf_-_@disp2133> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <875yy3850g.fsf_-_@disp2133> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 24, 2021 at 01:57:35PM -0500, Eric W. Biederman wrote: > So far the code has been lightly tested, and the descriptions of some > of the patches are a bit light, but I think this shows the direction > I am aiming to travel for sorting out exit(2) and exit_group(2). FWIW, here's the current picture for do_exit(), aside of exit(2) and do_exit_group(): 1) stuff that is clearly oops-like - alpha:die_if_kernel() alpha:do_entUna() alpha:do_page_fault() arm:oops_end() arm:__do_kernel_fault() arm64:die() arm64:die_kernel_fault() csky:alignment() csky:die() csky:no_context() h8300:die() h8300:do_page_fault() hexagon:die() ia64:die() i64:ia64_do_page_fault() m68k:die_if_kernel() m68k:send_fault_sig() microblaze:die() mips:die() nds32:handle_fpu_exception() nds32:die() nds32:unhandled_interruption() nds32:unhandled_exceptions() nds32:do_revinsn() nds32:do_page_fault() nios:die() openrisc:die() openrisc:do_page_fault() parisc:die_if_kernel() ppc:oops_end() riscv:die() riscv:die_kernel_fault() s390:die() s390:do_no_context() s390:do_low_address() sh:die() sparc32:die_if_kernel() sparc32:do_sparc_fault() sparc64:die_if_kernel() x86:rewind_stack_do_exit() xtensa:die() xtensa:bad_page_fault() We really do not want ptrace anywhere near any of those and we do not want any of that to return; this shit would better be handled right there and there - no "post a fatal signal" would do. 2) sparc32 playing silly buggers with SIGILL in case when signal delivery can't get a valid sigframe. The regular variant for that kind of stuff is forced SIGSEGV from failure case of signal_setup_done(). We could force that SIGILL instead of do_exit() there (and report failure from sigframe setup), but I suspect that we'll get SIGSEGV override that SIGILL, with user-visible behaviour change. Triggered by altstack overflow on sparc32; sparc64 gets SIGSEGV in the same situation, just like everybody else. 3) ppc swapcontext(2). Normal syscall, on failure results in exit(SIGSEGV). Not sure if we want to post signal here - exposing the caller to results of failure might be... interesting. And I really don't know if we want to allow ptrace() to poke around in the results of such failure. That's a question for ppc maintainers. 4) sparc32:try_to_clear_window_buffer(). Probably could force SIGSEGV instead of do_exit() there, but that might need a bit of massage in asm glue - it's called on the way out of kernel, right before handling signals. I'd like comments from davem on that one, though. 5) in xtensa fast_syscall_spill_registers() stuff. Might or might not be similar to the above. 6) sparc64 in tsb_grow() - looks like "impossible case, kill the sucker dead if that ever happens". Not sure if it's reachable at all. 7) s390 copy_thread() is doing something interesting in kernel thread case - frame->childregs.gprs[11] = (unsigned long)do_exit; AFAICS, had been unused since 30dcb0996e40, when s390 switched to new kernel_execve() semantics and kernel_thread_starter stopped using r11 (or proceeding to do_exit() in the first place). Ought to be removed, if s390 folks ACK that. 8) x86:emulate_vsyscall(), x86:save_v86_state(), m68k:fpsp040_die(), mips:bad_stack(), s390:__s390_handle_mcck(), ia64:mca_handler_bh(), s390:default_trap_handler() - fuck knows. 9) seccomp stuff - this one should *NOT* be switched to posting signals; it's on syscall_trace_enter() paths and we'd better have signal-equivalent environment there. We sure as hell do have regular "stop and let tracer poke around" in the same area - that's where strace is poking around. 10) there's a (moderate) bunch of places all over the tree where we have kthread() payload hit do_exit(), with or without complete() or module_put(). No ptrace stuff is going to be hit there and I see no point in switching those to posting anything. In particular, module_put_and_exit() sure as hell does *NOT* want to return to caller - it might've been unmapped by the point we are done. This do_exit() should really be noreturn. 11) abuses in kernel/kthread.c; AFAICS, it's misused as a mechanism to return an error value to parent. No ptrace possible (parent definitely not traced) and I don't see any point in delaying the handling of that do_exit() either (same as with the execve failure in call_usermodehelper_exec_async()). 12) io-uring threads hitting do_exit(). These, apparently, can be ptraced... 13) there's bdflush(1, whatever), which is equivalent to exit(0). IMO it's long past the time to simply remove the sucker. 14) reboot(2) stuff. No idea. 15) syscall_user_dispatch(). Didn't have time to look through that stuff in details yet, so no idea at the moment.