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=-8.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 F14F2C54FCC for ; Mon, 20 Apr 2020 22:24:56 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 4CD3B206DD for ; Mon, 20 Apr 2020 22:24:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ubLDLsXE" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4CD3B206DD Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-18580-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 30353 invoked by uid 550); 20 Apr 2020 22:24:48 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 30327 invoked from network); 20 Apr 2020 22:24:48 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=DV6jlkNA0aYuGGTHJFqAlVIWbRQ6V/i9e8cl7YrriE0=; b=ubLDLsXEcS+gRy7NCuBS0U8hRfvDH8rbExG4hDMZ/UPB3Z0OlbN5956SCN9w+6vt4s i83qKMAoJ8s6PECVYrrc48ILh1tnEurqEwv6c7qI9bHt4RPg/ZBGxoaZyy/j42XiO4dZ szcTBlYZ8evRbhYds+7lmWbRUWuouJm359n2RL7FTpFj1Nv1nKihW9WTUcwiDozzD5WY y79OD8sZ5VE5Gw8TQs24EtaXvjyqhd4U03u/RPmN+nWebpW7jIQxR6i14XX2UtNodQmJ G8FQ1K1xAaTx89lJDQ/zwRRShkgammuw55ZrtUzq7jvDzTQEV7jKgg9hy2uo610Rayz4 c41A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=DV6jlkNA0aYuGGTHJFqAlVIWbRQ6V/i9e8cl7YrriE0=; b=F/l/hj/XBE5jj7q9tg5j/7ITg3sSoVKwN9rD9xGjDF4Fz4k+iXv5FTQBuAu8q8C7Fm N9keS0WKG/wFcd7UPXijpSHGkptpbd2847Br+cmUFh+1z2gylijDUhp8m7q3Mof1iu/O eGIVDgjjN6TAmQOQ7OR28+CSCjsYxi9/3zGzH6LMbNnmJp67CZ+rDsuDKnUdDnBgPfn2 I7Gk5ypJ/oGZTy0ChW9Qn6Cex56bkn4QneNhbqfnRfapMZxl770z274mRlQsNSvlVWvp GOzuy1iO4JELk2ZmVpmkbXxWp2Y/jwSg0Vgx0uu4VXQ76pXvFuxLjAQIpPpf2PYmm3Ah makw== X-Gm-Message-State: AGi0PuahEF7gZg+QimxzrtWL1pns6Pa8XXaBtNBd3CDK9SD8Q99nhnop Mz0B8Q0s+AOm+7SL00pyZYM2uw== X-Google-Smtp-Source: APiQypK3lXJJ8OnZ7ClIxD0BeYEB6XEfm/pjTCKJqF60XnIqxkjWXsIItatZa73ZW9cYSXO2hPmHIw== X-Received: by 2002:a63:df0a:: with SMTP id u10mr18587666pgg.79.1587421475507; Mon, 20 Apr 2020 15:24:35 -0700 (PDT) Date: Mon, 20 Apr 2020 15:24:28 -0700 From: Sami Tolvanen To: Will Deacon Cc: Catalin Marinas , James Morse , Steven Rostedt , Ard Biesheuvel , Mark Rutland , Masahiro Yamada , Michal Marek , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dave Martin , Kees Cook , Laura Abbott , Marc Zyngier , Masami Hiramatsu , Nick Desaulniers , Jann Horn , Miguel Ojeda , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v11 03/12] scs: add support for stack usage debugging Message-ID: <20200420222428.GB77284@google.com> References: <20191018161033.261971-1-samitolvanen@google.com> <20200416161245.148813-1-samitolvanen@google.com> <20200416161245.148813-4-samitolvanen@google.com> <20200420171741.GC24386@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200420171741.GC24386@willie-the-truck> On Mon, Apr 20, 2020 at 06:17:42PM +0100, Will Deacon wrote: > > +#ifdef CONFIG_DEBUG_STACK_USAGE > > +static inline unsigned long scs_used(struct task_struct *tsk) > > +{ > > + unsigned long *p = __scs_base(tsk); > > + unsigned long *end = scs_magic(p); > > + unsigned long s = (unsigned long)p; > > + > > + while (p < end && READ_ONCE_NOCHECK(*p)) > > + p++; > > I think the expectation is that the caller has already checked that the > stack is not corrupted, so I'd probably throw a couple of underscores > in front of the function name, along with a comment. Correct. I'll do that. > Also, is tsk ever != current? This is only called from scs_release(), so tsk is never current. > > +static void scs_check_usage(struct task_struct *tsk) > > +{ > > + static DEFINE_SPINLOCK(lock); > > + static unsigned long highest; > > + unsigned long used = scs_used(tsk); > > + > > + if (used <= highest) > > + return; > > + > > + spin_lock(&lock); > > + > > + if (used > highest) { > > + pr_info("%s (%d): highest shadow stack usage: %lu bytes\n", > > + tsk->comm, task_pid_nr(tsk), used); > > + highest = used; > > + } > > + > > + spin_unlock(&lock); > > Do you really need this lock? I'd have thought you could cmpxchg() > highest instead. This is similar to check_stack_usage in kernel/exit.c, but yes, I can change this to a cmpxchg() loop instead. Sami