From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot1-x341.google.com (mail-ot1-x341.google.com [IPv6:2607:f8b0:4864:20::341]) by sourceware.org (Postfix) with ESMTPS id 630CA3950C76 for ; Mon, 5 Oct 2020 21:17:43 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 630CA3950C76 Received: by mail-ot1-x341.google.com with SMTP id n61so10100078ota.10 for ; Mon, 05 Oct 2020 14:17:43 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=hyrdjCdnHrdnldaqzFTSI9iGwYW5D1gYzC8h8Hdh80E=; b=IlyKHMILOtcIs9B+2LSp67Zn1RCFL5Q0GdNQhJi69V4NkD8vSiw0dj0H+XQyAET+tJ vBbqPljCerA37i5KIGYUs3DvU/szfpirlr7kLmlA92bCF4Ky+7k2NPU8BBA0DDflQ7FS IMfZ5azPdRSvDFeQmF7PE/VTr6dyW6uP94qBQr+ilQWwG9roxkNlCgZ78/S2j+JGMSQP cnmnV1M/u+2PmUC0+l/wSxIcbtHv0I5ECcw7vujNdVpaTSm2ZIBKldXYjZLL/apqF17g e8cyVFRROMGKt2AkOPKJB9y7k/Df+S0egx6hjXAbigSz3pTUzFk59qn1b7K33E6q7wHF ZaXQ== X-Gm-Message-State: AOAM531uw/TLYl5O7D4HMzmB9rsTbiMXLb/dNoigZSBZ4wy4B88maNqf rRIH6yUDwdOVTDLmoOyJMFdip1Avzx4R2KaDsu8= X-Google-Smtp-Source: ABdhPJwsw1a1+5vVblSv5qH5DSnI+PjKy8oR+ovdmUsJkjIp8Zb5VId6ArhnL/Vpg4zMKTCYJeDQKOpsUSVTyu76Klw= X-Received: by 2002:a9d:5545:: with SMTP id h5mr807618oti.269.1601932662759; Mon, 05 Oct 2020 14:17:42 -0700 (PDT) MIME-Version: 1.0 References: <20200929205746.6763-1-chang.seok.bae@intel.com> <20201005134534.GT6642@arm.com> In-Reply-To: <20201005134534.GT6642@arm.com> From: "H.J. Lu" Date: Mon, 5 Oct 2020 14:17:06 -0700 Message-ID: Subject: Re: [RFC PATCH 0/4] x86: Improve Minimum Alternate Stack Size To: Dave Martin Cc: "Chang S. Bae" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , "the arch/x86 maintainers" , Len Brown , Dave Hansen , Michael Ellerman , Tony Luck , "Ravi V. Shankar" , GNU C Library , linux-arch , Linux API , LKML Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3030.7 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 05 Oct 2020 21:17:44 -0000 On Mon, Oct 5, 2020 at 6:45 AM Dave Martin wrote: > > 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... Here is my proposal for glibc: https://sourceware.org/pipermail/libc-alpha/2020-September/118098.html 1. Define SIGSTKSZ and MINSIGSTKSZ to 64KB. 2. Add _SC_RSVD_SIG_STACK_SIZE for signal stack size reserved by the kernel. 3. Deprecate SIGSTKSZ and MINSIGSTKSZ if _SC_RSVD_SIG_STACK_SIZE is in use. -- H.J.