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=-10.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 1E234C433E0 for ; Thu, 6 Aug 2020 22:39:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1BFAF2086A for ; Thu, 6 Aug 2020 22:39:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="oWwFoqGb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725999AbgHFWjB (ORCPT ); Thu, 6 Aug 2020 18:39:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40790 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725947AbgHFWjB (ORCPT ); Thu, 6 Aug 2020 18:39:01 -0400 Received: from mail-oi1-x243.google.com (mail-oi1-x243.google.com [IPv6:2607:f8b0:4864:20::243]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2B9F4C061574; Thu, 6 Aug 2020 15:39:01 -0700 (PDT) Received: by mail-oi1-x243.google.com with SMTP id l204so190990oib.3; Thu, 06 Aug 2020 15:39:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Ne1iYZprPZsaiWqWZFllfuyUnxnmRkcPCgewhYs7+po=; b=oWwFoqGba2t65iV+0hVJvoo34WVzexMPem5bmNrBL2po0vMgi7NmTYQnYyI/pK9BPL JEeCUzLouqqweosS1VJ3yAv/DIUZ58V2TeGJV+2vBVGcGw5DgK0PIliW/SRbGaYI69RM aw/fTT5Kwv9QtuMRO1O32xkqGq6citRBosNGQc1Fkf8vgCgxzsXc+iuZfcjFVa+9W9mJ P95qUCukRV+2zlroNs8CYWd8S7AuoLWQns9qNS/q4DiPOzzAg9r3uSEah1PBfRMaEVw8 xHHv0C9s3+5LRHBRnuAQDkWMUPjzLeV5xx9lgb8J1li9YC6gpmudNnGNnS7ByakiCOH6 MafQ== 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=Ne1iYZprPZsaiWqWZFllfuyUnxnmRkcPCgewhYs7+po=; b=qUm2jD7p7OgbeKqYkM8m+uiyc0ASrxRykyyPX4qUfoLaq6ydsHcI8rOpFQxu1xqQgV cB8+AUIXWC2gVLHFVuyydBCnPhjxrVKWcjVoomC2jjSHttrxGeWgHHMesjwLNfirMYg+ 2UvlBB7KOiWfAD7bV8HXY8KehYMgKkr+COl47Usqt+rXqzNNmgyASdGbOvAMAwrQPKhD htmrpplY4UuJRtWAh1uBvriJVCVGR2lTGLHKOpKN3HK2qWytfmOm5RewCkUZ1LnfVvhM Y/ncV+wZIwUqIUPxT8Yl2MuEbtc2OPwUYTNbIie3qno0RKnI2jEhVuNFJIe+Ca64iCge vpvg== X-Gm-Message-State: AOAM533MjdhcnFheyJMQlCuSrFli8N7pevcbgHBgrNzhzloVTQvpN7/V lRz2eXgPt6K2Q3cXTPbYVk2tzJ22z/BkGhUxIn0= X-Google-Smtp-Source: ABdhPJw24FLE0cOWVKOoxoFIzofMAQlqhvnejmnRS9N4YG08WW27U7QHzTUC4wI/BCAaa2dgO3tta2o3+MD5w0Lq8pI= X-Received: by 2002:aca:2306:: with SMTP id e6mr9080081oie.108.1596753539610; Thu, 06 Aug 2020 15:38:59 -0700 (PDT) MIME-Version: 1.0 References: <20200730205112.2099429-1-ndesaulniers@google.com> <20200730205112.2099429-3-ndesaulniers@google.com> In-Reply-To: <20200730205112.2099429-3-ndesaulniers@google.com> From: Nathan Huckleberry Date: Thu, 6 Aug 2020 17:38:46 -0500 Message-ID: Subject: Re: [PATCH 2/4] ARM: backtrace-clang: add fixup for lr dereference To: Nick Desaulniers Cc: Russell King , Andrew Morton , Chunyan Zhang , clang-built-linux@googlegroups.com, Dmitry Safonov <0x7f454c46@gmail.com>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org, Lvqiang Huang , Matthias Brugger , Miles Chen , stable@vger.kernel.org, Nathan Huckleberry Content-Type: text/plain; charset="UTF-8" Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org Mostly looks good to me. Just a minor nit. On Thu, Jul 30, 2020 at 3:51 PM Nick Desaulniers wrote: > > If the value of the link register is not correct (tail call from asm > that didn't set it, stack corruption, memory no longer mapped), then > using it for an address calculation may trigger an exception. Without a > fixup handler, this will lead to a panic, which will unwind, which will > trigger the fault repeatedly in an infinite loop. > > We don't observe such failures currently, but we have. Just to be safe, > add a fixup handler here so that at least we don't have an infinite > loop. > > Cc: stable@vger.kernel.org > Fixes: commit 6dc5fd93b2f1 ("ARM: 8900/1: UNWINDER_FRAME_POINTER implementation for Clang") > Reported-by: Miles Chen > Signed-off-by: Nick Desaulniers > --- > arch/arm/lib/backtrace-clang.S | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/arch/arm/lib/backtrace-clang.S b/arch/arm/lib/backtrace-clang.S > index 5388ac664c12..40eb2215eaf4 100644 > --- a/arch/arm/lib/backtrace-clang.S > +++ b/arch/arm/lib/backtrace-clang.S > @@ -146,7 +146,7 @@ for_each_frame: tst frame, mask @ Check for address exceptions > > tst sv_lr, #0 @ If there's no previous lr, > beq finished_setup @ we're done. > - ldr r0, [sv_lr, #-4] @ get call instruction > +prev_call: ldr r0, [sv_lr, #-4] @ get call instruction > ldr r3, .Lopcode+4 > and r2, r3, r0 @ is this a bl call > teq r2, r3 > @@ -206,6 +206,13 @@ finished_setup: > mov r2, frame > bl printk > no_frame: ldmfd sp!, {r4 - r9, fp, pc} > +/* > + * Accessing the address pointed to by the link register triggered an > + * exception, don't try to unwind through it. > + */ > +bad_lr: mov sv_fp, #0 It might be nice to emit a warning here since we'll only hit this case if something fishy is going on with the saved lr. > + mov sv_lr, #0 > + b finished_setup > ENDPROC(c_backtrace) > .pushsection __ex_table,"a" > .align 3 > @@ -214,6 +221,7 @@ ENDPROC(c_backtrace) > .long 1003b, 1006b > .long 1004b, 1006b > .long 1005b, 1006b > + .long prev_call, bad_lr > .popsection > > .Lbad: .asciz "%sBacktrace aborted due to bad frame pointer <%p>\n" > -- > 2.28.0.163.g6104cc2f0b6-goog > Thanks, Huck