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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 39854C4363D for ; Mon, 5 Oct 2020 13:45:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DEA6D20756 for ; Mon, 5 Oct 2020 13:45:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726398AbgJENpl (ORCPT ); Mon, 5 Oct 2020 09:45:41 -0400 Received: from foss.arm.com ([217.140.110.172]:47844 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725936AbgJENpk (ORCPT ); Mon, 5 Oct 2020 09:45:40 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 96F92106F; Mon, 5 Oct 2020 06:45:39 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9B6933F70D; Mon, 5 Oct 2020 06:45:37 -0700 (PDT) Date: Mon, 5 Oct 2020 14:45:34 +0100 From: Dave Martin To: "Chang S. Bae" Cc: tglx@linutronix.de, mingo@kernel.org, bp@suse.de, luto@kernel.org, x86@kernel.org, len.brown@intel.com, dave.hansen@intel.com, hjl.tools@gmail.com, mpe@ellerman.id.au, tony.luck@intel.com, ravi.v.shankar@intel.com, libc-alpha@sourceware.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/4] x86: Improve Minimum Alternate Stack Size Message-ID: <20201005134534.GT6642@arm.com> References: <20200929205746.6763-1-chang.seok.bae@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200929205746.6763-1-chang.seok.bae@intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 29, 2020 at 01:57:42PM -0700, Chang S. Bae wrote: > During signal entry, the kernel pushes data onto the normal userspace > stack. On x86, the data pushed onto the user stack includes XSAVE state, > which has grown over time as new features and larger registers have been > added to the architecture. > > MINSIGSTKSZ is a constant provided in the kernel signal.h headers and > typically distributed in lib-dev(el) packages, e.g. [1]. Its value is > compiled into programs and is part of the user/kernel ABI. The MINSIGSTKSZ > constant indicates to userspace how much data the kernel expects to push on > the user stack, [2][3]. > > However, this constant is much too small and does not reflect recent > additions to the architecture. For instance, when AVX-512 states are in > use, the signal frame size can be 3.5KB while MINSIGSTKSZ remains 2KB. > > The bug report [4] explains this as an ABI issue. The small MINSIGSTKSZ can > cause user stack overflow when delivering a signal. > > In this series, we suggest a couple of things: > 1. Provide a variable minimum stack size to userspace, as a similar > approach to [5] > 2. Avoid using a too-small alternate stack I can't comment on the x86 specifics, but the approach followed in this series does seem consistent with the way arm64 populates AT_MINSIGSTKSZ. I need to dig up my glibc hacks for providing a sysconf interface to this... Cheers ---Dave > > [1]: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/bits/sigstack.h;h=b9dca794da093dc4d41d39db9851d444e1b54d9b;hb=HEAD > [2]: https://www.gnu.org/software/libc/manual/html_node/Signal-Stack.html > [3]: https://man7.org/linux/man-pages/man2/sigaltstack.2.html > [4]: https://bugzilla.kernel.org/show_bug.cgi?id=153531 > [5]: https://blog.linuxplumbersconf.org/2017/ocw/system/presentations/4671/original/plumbers-dm-2017.pdf > > Chang S. Bae (4): > x86/signal: Introduce helpers to get the maximum signal frame size > x86/elf: Support a new ELF aux vector AT_MINSIGSTKSZ > x86/signal: Prevent an alternate stack overflow before a signal > delivery > selftest/x86/signal: Include test cases for validating sigaltstack > > arch/x86/ia32/ia32_signal.c | 11 +- > arch/x86/include/asm/elf.h | 4 + > arch/x86/include/asm/fpu/signal.h | 2 + > arch/x86/include/asm/sigframe.h | 25 +++++ > arch/x86/include/uapi/asm/auxvec.h | 6 +- > arch/x86/kernel/cpu/common.c | 3 + > arch/x86/kernel/fpu/signal.c | 20 ++++ > arch/x86/kernel/signal.c | 66 +++++++++++- > tools/testing/selftests/x86/Makefile | 2 +- > tools/testing/selftests/x86/sigaltstack.c | 126 ++++++++++++++++++++++ > 10 files changed, 258 insertions(+), 7 deletions(-) > create mode 100644 tools/testing/selftests/x86/sigaltstack.c > > -- > 2.17.1 >