From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on gnuweeb.org X-Spam-Level: X-Spam-Status: No, score=-7.6 required=5.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_SOFTFAIL,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.6 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 138C9C43334 for ; Thu, 14 Jul 2022 20:57:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240473AbiGNU47 (ORCPT ); Thu, 14 Jul 2022 16:56:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37150 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232389AbiGNU45 (ORCPT ); Thu, 14 Jul 2022 16:56:57 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 06F396BC1D for ; Thu, 14 Jul 2022 13:56:57 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id i9-20020a258b09000000b0066efe437da6so2457244ybl.5 for ; Thu, 14 Jul 2022 13:56:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:message-id:mime-version:subject:from:to:cc; bh=QUqpeU8M4eT15MSqD/BnartlfIY7kCYtJMFstSRxuF8=; b=NyEeYk2hC69eFMaSk0Josx4oxWR1Fw4LfEAYWwZxyp575imGZDYXhsKWYy50e9F+Bo YGPxB9QU2iqkEiA6h7gMhlOK8fFpLRXEijEBPs9FQPw7rG1KQvyXn4LMsrSlfjCrNlIl 2xgTGZfmTH0qM41NM9B2AujqAAzkK5KughTx8Aaxh/IJ8kDoLigS5lb4bVYCEaHmjb0V y0HTyc71eCPL3GlhFvxZ5CvHY88UH3w9Lv4+lGItJEUhk/2QcAbUhJ2sex6rz5Q6oxgH ZqrqciQ8psIEwofly+ywHyNrweQKgL9dgQ7LRsKFe/wm2cHmJkhw/TQCRCSUYm49RrEQ M7Uw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=QUqpeU8M4eT15MSqD/BnartlfIY7kCYtJMFstSRxuF8=; b=tN/zCHorI8z/kjeoYpQeoeIxL/0x8sGJH95x4H7tcJeW1ey6MmzoxPOOEQkKl/KPYi vl9zWG7bp0feb462TPpTrb/HGmIPXC9B/wP6JGuFpEP27LoSHAKGdInXs6jfGCr3DjaH WSYlLIigyoFaRL/FjIPg5zwOQqUWbyDZ28R4YIfxpIkHcyuiQDXZHUSgr+dhcJz/XHJW C3nFnrYg6Ncoe+hD+Du86m+6Jx0w8Qb8FBDK8PzvntDJGZnRUkoSL7wOLqimmZMXZajm Nc3oWVn0EZ+UtUTu761d+zjR0PwsJ8684Nidz8TFfoNjWLVNexFkSIMgRyg/sJPKvM57 17zg== X-Gm-Message-State: AJIora9Ewi8Jc2DQClR+DlRjOolP+63UK/MI27NAS1L+efIhYB15SFAt 0tVEIT5yR2cc39/j+0Qh0iGv5GKb2KsyKLxoMJo= X-Google-Smtp-Source: AGRyM1vmKTM1FaMh8eU2urAb2+GraZv12lCqQp6YihgU9kbN0pGejEVllwkey8v+ez9pXys1HIiTU3tYEB6dltut3lA= X-Received: from ndesaulniers1.mtv.corp.google.com ([2620:15c:211:202:4bc2:7a2b:c53a:2dfb]) (user=ndesaulniers job=sendgmr) by 2002:a81:4a0b:0:b0:31d:b645:84e8 with SMTP id x11-20020a814a0b000000b0031db64584e8mr12085251ywa.239.1657832216295; Thu, 14 Jul 2022 13:56:56 -0700 (PDT) Date: Thu, 14 Jul 2022 13:56:43 -0700 Message-Id: <20220714205646.4023495-1-ndesaulniers@google.com> Mime-Version: 1.0 X-Developer-Key: i=ndesaulniers@google.com; a=ed25519; pk=lvO/pmg+aaCb6dPhyGC1GyOCvPueDrrc8Zeso5CaGKE= X-Developer-Signature: v=1; a=ed25519-sha256; t=1657832203; l=1877; i=ndesaulniers@google.com; s=20211004; h=from:subject; bh=Y4sBF3AutOxiL+SHsVeEMPpQpIermTXH5kEyp1GPq6s=; b=xAaXgfs85FDQXD5OVaEIdThMCupKgeKa7r1xcwZp0TJeZ/wzFgnNld9VUOf2smHAxawT1Tl+RB0i 41zv0RrbCoTKsJJu944BR/UI3/BuEGBX+ihO/SpLluzyQ46i8YUm X-Mailer: git-send-email 2.37.0.170.g444d1eabd0-goog Subject: [PATCH] ubsan: disable UBSAN_DIV_ZERO for clang From: Nick Desaulniers To: Kees Cook Cc: Nick Desaulniers , Sudip Mukherjee , Linus Torvalds , Nathan Chancellor , Tom Rix , Marco Elver , Andrew Morton , Josh Poimboeuf , "Peter Zijlstra (Intel)" , linux-kernel@vger.kernel.org, llvm@lists.linux.dev Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Building with UBSAN_DIV_ZERO with clang produces numerous fallthrough warnings from objtool. In the case of uncheck division, UBSAN_DIV_ZERO may introduce new control flow to check for division by zero. Because the result of the division is undefined, LLVM may optimize the control flow such that after the call to __ubsan_handle_divrem_overflow doesn't matter. If panic_on_warn was set, __ubsan_handle_divrem_overflow would panic. The problem is is that panic_on_warn is run time configurable. If it's disabled, then we cannot guarantee that we will be able to recover safely. Disable this config for clang until we can come up with a solution in LLVM. Link: https://github.com/ClangBuiltLinux/linux/issues/1657 Link: https://github.com/llvm/llvm-project/issues/56289 Link: https://lore.kernel.org/lkml/CAHk-=wj1qhf7y3VNACEexyp5EbkNpdcu_542k-xZpzmYLOjiCg@mail.gmail.com/ Reported-by: Sudip Mukherjee Suggested-by: Linus Torvalds Signed-off-by: Nick Desaulniers --- Linus, I still think we should add explicit checks to gaurd against divide by zero. lib/Kconfig.ubsan | 3 +++ 1 file changed, 3 insertions(+) diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan index a9f7eb047768..fd15230a703b 100644 --- a/lib/Kconfig.ubsan +++ b/lib/Kconfig.ubsan @@ -84,6 +84,9 @@ config UBSAN_SHIFT config UBSAN_DIV_ZERO bool "Perform checking for integer divide-by-zero" depends on $(cc-option,-fsanitize=integer-divide-by-zero) + # https://github.com/ClangBuiltLinux/linux/issues/1657 + # https://github.com/llvm/llvm-project/issues/56289 + depends on !CC_IS_CLANG help This option enables -fsanitize=integer-divide-by-zero which checks for integer division by zero. This is effectively redundant with the -- 2.37.0.170.g444d1eabd0-goog