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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 41694C32788 for ; Thu, 11 Oct 2018 08:40:20 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DF1122087A for ; Thu, 11 Oct 2018 08:40:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DF1122087A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 42W4D20WFJzF3Hl for ; Thu, 11 Oct 2018 19:40:18 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 42W46k1QLwzF37s for ; Thu, 11 Oct 2018 19:35:42 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix, from userid 1034) id 42W46j650vz9sjF; Thu, 11 Oct 2018 19:35:41 +1100 (AEDT) X-powerpc-patch-notification: thanks X-powerpc-patch-commit: f5e284803a7206d43e26f9ffcae5de9626d95e37 In-Reply-To: <20181001062151.23831-1-dja@axtens.net> To: Daniel Axtens , linuxppc-dev@lists.ozlabs.org From: Michael Ellerman Subject: Re: powerpc/nohash: fix undefined behaviour when testing page size support Message-Id: <42W46j650vz9sjF@ozlabs.org> Date: Thu, 11 Oct 2018 19:35:41 +1100 (AEDT) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel Axtens Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, 2018-10-01 at 06:21:51 UTC, Daniel Axtens wrote: > When enumerating page size definitions to check hardware support, > we construct a constant which is (1U << (def->shift - 10)). > > However, the array of page size definitions is only initalised for > various MMU_PAGE_* constants, so it contains a number of 0-initialised > elements with def->shift == 0. This means we end up shifting by a > very large number, which gives the following UBSan splat: > > ================================================================================ > UBSAN: Undefined behaviour in /home/dja/dev/linux/linux/arch/powerpc/mm/tlb_nohash.c:506:21 > shift exponent 4294967286 is too large for 32-bit type 'unsigned int' > CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc3-00045-ga604f927b012-dirty #6 > Call Trace: > [c00000000101bc20] [c000000000a13d54] .dump_stack+0xa8/0xec (unreliable) > [c00000000101bcb0] [c0000000004f20a8] .ubsan_epilogue+0x18/0x64 > [c00000000101bd30] [c0000000004f2b10] .__ubsan_handle_shift_out_of_bounds+0x110/0x1a4 > [c00000000101be20] [c000000000d21760] .early_init_mmu+0x1b4/0x5a0 > [c00000000101bf10] [c000000000d1ba28] .early_setup+0x100/0x130 > [c00000000101bf90] [c000000000000528] start_here_multiplatform+0x68/0x80 > ================================================================================ > > Fix this by first checking if the element exists (shift != 0) before > constructing the constant. > > Signed-off-by: Daniel Axtens Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/f5e284803a7206d43e26f9ffcae5de cheers