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=-21.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,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 4457FC433E6 for ; Fri, 5 Feb 2021 19:09:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EDE5264EFE for ; Fri, 5 Feb 2021 19:09:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233557AbhBER1L (ORCPT ); Fri, 5 Feb 2021 12:27:11 -0500 Received: from mail.kernel.org ([198.145.29.99]:50324 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233529AbhBEROn (ORCPT ); Fri, 5 Feb 2021 12:14:43 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7C40E64DDD; Fri, 5 Feb 2021 18:56:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1612551385; bh=OkkSvVZU2knJ4p+uUP/pF7UlAvILdapZPwTt6d0nZJs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=f2VckE1ZDvWkIdIrvbOurhCnBuCidDOT4RIjd/B0eLV8lyPiyDbvneMsAXhrzPasR 78UfPWR7ac7eyLIJe9WQzjEsZyaMx3ZzeNV/Wdlf5jW4LaZkv0zOvqydcDrG1hkEry Yu6pfbjMKab6rwlZRziI9FUaprMrLKFEavyXwlIiQTTAlqZAt8nGB2WIuKOgOAWbDv HqUf2ArcgxA2+WPpkT7vj5g+340q/VrxbQ4tLqdZinaCk/3N5ut3LrW9X6e5RAUtx1 AB+X0HeUgeSVTYFi6ufpDVMGpPWZZfIteVilCbeH+BEZPbb9jEo3Z+9JnzNVlOpnfh ExfAZnGHY91SA== Date: Fri, 5 Feb 2021 11:56:22 -0700 From: Nathan Chancellor To: Borislav Petkov Cc: Arvind Sankar , Ard Biesheuvel , Arnd Bergmann , Thomas Gleixner , Ingo Molnar , X86 ML , Nathan Chancellor , Nick Desaulniers , Arnd Bergmann , Darren Hart , Andy Shevchenko , "H. Peter Anvin" , linux-efi , platform-driver-x86@vger.kernel.org, Linux Kernel Mailing List , clang-built-linux , "Kirill A. Shutemov" Subject: Re: [PATCH] x86/efi: Remove EFI PGD build time checks Message-ID: <20210205185622.GA461042@localhost> References: <20210118202409.GG30090@zn.tnic> <20210203185148.GA1711888@localhost> <20210204105155.GA32255@zn.tnic> <20210204221318.GI32255@zn.tnic> <20210205113930.GD17488@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210205113930.GD17488@zn.tnic> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 05, 2021 at 12:39:30PM +0100, Borislav Petkov wrote: > From: Borislav Petkov > > With CONFIG_X86_5LEVEL, CONFIG_UBSAN and CONFIG_UBSAN_UNSIGNED_OVERFLOW > enabled, clang fails the build with > > x86_64-linux-ld: arch/x86/platform/efi/efi_64.o: in function `efi_sync_low_kernel_mappings': > efi_64.c:(.text+0x22c): undefined reference to `__compiletime_assert_354' > > which happens due to -fsanitize=unsigned-integer-overflow being enabled: > > -fsanitize=unsigned-integer-overflow: Unsigned integer overflow, where > the result of an unsigned integer computation cannot be represented > in its type. Unlike signed integer overflow, this is not undefined > behavior, but it is often unintentional. This sanitizer does not check > for lossy implicit conversions performed before such a computation > (see -fsanitize=implicit-conversion). > > and that fires when the (intentional) EFI_VA_START/END defines overflow > an unsigned long, leading to the assertion expressions not getting > optimized away (on GCC they do)... > > However, those checks are superfluous: the runtime services mapping > code already makes sure the ranges don't overshoot EFI_VA_END as the > EFI mapping range is hardcoded. On each runtime services call, it is > switched to the EFI-specific PGD and even if mappings manage to escape > that last PGD, this won't remain unnoticed for long. > > So rip them out. > > See https://github.com/ClangBuiltLinux/linux/issues/256 for more info. > > Reported-by: Arnd Bergmann > Link: http://lkml.kernel.org/r/20210107223424.4135538-1-arnd@kernel.org > Signed-off-by: Borislav Petkov Reviewed-by: Nathan Chancellor Tested-by: Nathan Chancellor > --- > arch/x86/platform/efi/efi_64.c | 19 ------------------- > 1 file changed, 19 deletions(-) > > diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c > index e1e8d4e3a213..8efd003540ca 100644 > --- a/arch/x86/platform/efi/efi_64.c > +++ b/arch/x86/platform/efi/efi_64.c > @@ -115,31 +115,12 @@ void efi_sync_low_kernel_mappings(void) > pud_t *pud_k, *pud_efi; > pgd_t *efi_pgd = efi_mm.pgd; > > - /* > - * We can share all PGD entries apart from the one entry that > - * covers the EFI runtime mapping space. > - * > - * Make sure the EFI runtime region mappings are guaranteed to > - * only span a single PGD entry and that the entry also maps > - * other important kernel regions. > - */ > - MAYBE_BUILD_BUG_ON(pgd_index(EFI_VA_END) != pgd_index(MODULES_END)); > - MAYBE_BUILD_BUG_ON((EFI_VA_START & PGDIR_MASK) != > - (EFI_VA_END & PGDIR_MASK)); > - > pgd_efi = efi_pgd + pgd_index(PAGE_OFFSET); > pgd_k = pgd_offset_k(PAGE_OFFSET); > > num_entries = pgd_index(EFI_VA_END) - pgd_index(PAGE_OFFSET); > memcpy(pgd_efi, pgd_k, sizeof(pgd_t) * num_entries); > > - /* > - * As with PGDs, we share all P4D entries apart from the one entry > - * that covers the EFI runtime mapping space. > - */ > - BUILD_BUG_ON(p4d_index(EFI_VA_END) != p4d_index(MODULES_END)); > - BUILD_BUG_ON((EFI_VA_START & P4D_MASK) != (EFI_VA_END & P4D_MASK)); > - > pgd_efi = efi_pgd + pgd_index(EFI_VA_END); > pgd_k = pgd_offset_k(EFI_VA_END); > p4d_efi = p4d_offset(pgd_efi, 0); > -- > 2.29.2 > > -- > Regards/Gruss, > Boris. > > https://people.kernel.org/tglx/notes-about-netiquette