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=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, 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 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 1CB5DC433F5 for ; Mon, 13 Sep 2021 16:48:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0195F60F24 for ; Mon, 13 Sep 2021 16:48:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239251AbhIMQt2 (ORCPT ); Mon, 13 Sep 2021 12:49:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:42560 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238219AbhIMQt1 (ORCPT ); Mon, 13 Sep 2021 12:49:27 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id C657760F26; Mon, 13 Sep 2021 16:48:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631551691; bh=dgZoCqLRf7yYWTZPvAE8JfsdZ8bcTrri+VeUGd3Iql0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=J7krykSzHQ2oEYzswpeqbkf6gI29sZwJe/8kAJPOfbPnLkn2PamRUl9wC/DzveXLP GhNrMiSeoscNezVWufm1PfIf8FfSYdsQikMUOe1jDqDOpG6rjReQ8BpZBEEcjwAZhn gYlWxk+2izBA93AwNrdz5EcHCLNkjkcVnjHpe4eM= Date: Mon, 13 Sep 2021 18:48:09 +0200 From: Greg Kroah-Hartman To: Will Deacon Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Nick Desaulniers , Bill Wendling , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Peter Zijlstra Subject: Re: [PATCH] x86/uaccess: Fix 32-bit __get_user_asm_u64() when CC_HAS_ASM_GOTO_OUTPUT=y Message-ID: References: <20210913163547.5156-1-will@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210913163547.5156-1-will@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 13, 2021 at 05:35:47PM +0100, 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 > 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 > --- > 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 > Tested-by: Greg Kroah-Hartman Thanks for finding and fixing this! greg k-h