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=-23.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 C37F5C433F5 for ; Mon, 13 Sep 2021 16:46:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A739260F36 for ; Mon, 13 Sep 2021 16:46:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239230AbhIMQrZ (ORCPT ); Mon, 13 Sep 2021 12:47:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49278 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239107AbhIMQrU (ORCPT ); Mon, 13 Sep 2021 12:47:20 -0400 Received: from mail-lf1-x12d.google.com (mail-lf1-x12d.google.com [IPv6:2a00:1450:4864:20::12d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1F23FC061574 for ; Mon, 13 Sep 2021 09:46:04 -0700 (PDT) Received: by mail-lf1-x12d.google.com with SMTP id i25so18446095lfg.6 for ; Mon, 13 Sep 2021 09:46:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=4AWqq8PdF0T27j1u4r8SJdSDQAmnIa798/DXEHvOpSI=; b=FU+bAjJMm7Th8TwF7GGVELgB1n/Ftr6IutqHVydD9w8PX1GQcf6GzsLJOqGGh6CW0l EgHYwD/xUZZOVDsGOol3BaZ8xHn83V7/OXyGzkFbGAGnI2UYFevtlAxVK0miRIcA5sma 7ChEqHKPnv+jjr4rq9563XtC1/WAT8qcu+Bu7KgwmwaedbS/lr08mFRMX8yVsveRl3dO fkLTwlz3V17XMGEE2CT1WMP4SCJwRxX6N5cqDDMKSzUVH2QVfP4XIwCjwyqgdH3MERlO vZR1EV6lwCy9I9JF6m4YNjNRIsj/BeIG+3ZUtcKRVlTuJJG9gt3JEr6a+crt5Rin8pfL MU5g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=4AWqq8PdF0T27j1u4r8SJdSDQAmnIa798/DXEHvOpSI=; b=fb+lrw89tZpSU1l266W5gBJIn02njl/KXedttcHUSM3FTCN4rYuEfs0SZ9vEfuHeiu Ttj1llukfWakfaFod9qSwE9k03J1iFEUcRd67F8lhHmOjMY3NBQEF4N/YDv24QUTQAT0 J+GOTQRnPTV63vdrXOxf0LnQI8iupvPJ78mo05G+bHpyq9XjL9PlkKtNYhwYMU4akJu4 s/taZ/NDvUz5K+KaQi4Gxd34yPEkVHqyzENgyO+EsaFoPItzpJetWAzrkzj/mGcmLVM7 9HtD32K2pAr5uk/MgIFY2EiPUU86sEoIPwn6oCds06O2Nal9YXkyGPXi7k8S61n+5+Ig 7wEA== X-Gm-Message-State: AOAM533KBTFdF7FF+8Pg7AFCyKTUpcy3yM7o0Io9s74SI7U6tJBaulH2 xLb2dtIKYP4WYK40SoYXz74H93YknsfLZircAJhxAA== X-Google-Smtp-Source: ABdhPJyr2c+1gD5MNC+tqhvxKv/vc4WNHyPe6OFeOs4hvUvdmby0LD98BjnKqvYF/pKBwcggQnXp9YvzSMG63YviiFw= X-Received: by 2002:a05:6512:139c:: with SMTP id p28mr9178591lfa.523.1631551562217; Mon, 13 Sep 2021 09:46:02 -0700 (PDT) MIME-Version: 1.0 References: <20210913163547.5156-1-will@kernel.org> In-Reply-To: <20210913163547.5156-1-will@kernel.org> From: Nick Desaulniers Date: Mon, 13 Sep 2021 09:45:51 -0700 Message-ID: Subject: Re: [PATCH] x86/uaccess: Fix 32-bit __get_user_asm_u64() when CC_HAS_ASM_GOTO_OUTPUT=y To: Will Deacon Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Bill Wendling , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Peter Zijlstra , Greg Kroah-Hartman Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 13, 2021 at 9:36 AM Will Deacon wrote: > > Commit 865c50e1d279 ("x86/uaccess: utilize CONFIG_CC_HAS_ASM_GOTO_OUTPUT") > added an optimised version of __get_user_asm() for x86 using 'asm goto'. > > Like the non-optimised code, the 32-bit implementation of 64-bit get_user() > expands to a pair of 32-bit accesses. Unlike the non-optimised code, the > _original_ pointer is incremented to copy the high word instead of loading > through a new pointer explicitly constructed to point at a 32-bit type. > Consequently, if the pointer points at a 64-bit type then we end up > loading the wrong data for the upper 32-bits. > > This was observed as a mount() failure in Android targetting i686 after s/targetting/targeting/ > b0cfcdd9b967 ("d_path: make 'prepend()' fill up the buffer exactly on > overflow") because the call to copy_from_kernel_nofault() from > prepend_copy() ends up in __get_kernel_nofault() and casts the source > pointer to a 'u64 __user *'. An attempt to mount at "/debug_ramdisk" > therefore ends up failing trying to mount "/debumdismdisk". > > Use the existing '__gu_ptr' source pointer to unsigned int for 32-bit > __get_user_asm_u64() instead of the original pointer. > > Cc: Nick Desaulniers > Cc: Bill Wendling > Cc: Linus Torvalds > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: Borislav Petkov > Cc: Peter Zijlstra > Reported-by: Greg Kroah-Hartman > Fixes: 865c50e1d279 ("x86/uaccess: utilize CONFIG_CC_HAS_ASM_GOTO_OUTPUT") > Signed-off-by: Will Deacon Sorry I missed this; I think -Wunused-variable would have helped here. Thanks for debugging+fixing. Reviewed-by: Nick Desaulniers > --- > arch/x86/include/asm/uaccess.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h > index c9fa7be3df82..5c95d242f38d 100644 > --- a/arch/x86/include/asm/uaccess.h > +++ b/arch/x86/include/asm/uaccess.h > @@ -301,8 +301,8 @@ do { \ > unsigned int __gu_low, __gu_high; \ > const unsigned int __user *__gu_ptr; \ > __gu_ptr = (const void __user *)(ptr); \ > - __get_user_asm(__gu_low, ptr, "l", "=r", label); \ > - __get_user_asm(__gu_high, ptr+1, "l", "=r", label); \ > + __get_user_asm(__gu_low, __gu_ptr, "l", "=r", label); \ > + __get_user_asm(__gu_high, __gu_ptr+1, "l", "=r", label); \ > (x) = ((unsigned long long)__gu_high << 32) | __gu_low; \ > } while (0) > #else > -- > 2.33.0.309.g3052b89438-goog > -- Thanks, ~Nick Desaulniers