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=-23.8 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,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 555E8C4361A for ; Fri, 5 Mar 2021 12:29:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1FEB065013 for ; Fri, 5 Mar 2021 12:29:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232062AbhCEM2m (ORCPT ); Fri, 5 Mar 2021 07:28:42 -0500 Received: from mail.kernel.org ([198.145.29.99]:36724 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231958AbhCEM2K (ORCPT ); Fri, 5 Mar 2021 07:28:10 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 6BC0365029; Fri, 5 Mar 2021 12:28:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1614947290; bh=H80drgz2QjWFLzCaXPaW80pTjIGTtPm5BOLLnJQx5gs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OKKSiRI2ngB04VRQSih3nihzwKsxu6NDEd5zoH2r4k1yKBhDlJ3N5PUcS+KxREyz0 E3kPLFui6NFgjzuEiFc++xGaGFJDwHiGY7mN4xqPu8ScMWN+Ba8yKuOYVcK84QnLpr VrSAKyGTNJElMeMt1NF28+Fi/P0K9hcSqHkku0Cg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Arnd Bergmann , Fangrui Song , Borislav Petkov , Nick Desaulniers , Nathan Chancellor , Sedat Dilek Subject: [PATCH 5.10 005/102] x86/build: Treat R_386_PLT32 relocation as R_386_PC32 Date: Fri, 5 Mar 2021 13:20:24 +0100 Message-Id: <20210305120903.544895650@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210305120903.276489876@linuxfoundation.org> References: <20210305120903.276489876@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Fangrui Song commit bb73d07148c405c293e576b40af37737faf23a6a upstream. This is similar to commit b21ebf2fb4cd ("x86: Treat R_X86_64_PLT32 as R_X86_64_PC32") but for i386. As far as the kernel is concerned, R_386_PLT32 can be treated the same as R_386_PC32. R_386_PLT32/R_X86_64_PLT32 are PC-relative relocation types which can only be used by branches. If the referenced symbol is defined externally, a PLT will be used. R_386_PC32/R_X86_64_PC32 are PC-relative relocation types which can be used by address taking operations and branches. If the referenced symbol is defined externally, a copy relocation/canonical PLT entry will be created in the executable. On x86-64, there is no PIC vs non-PIC PLT distinction and an R_X86_64_PLT32 relocation is produced for both `call/jmp foo` and `call/jmp foo@PLT` with newer (2018) GNU as/LLVM integrated assembler. This avoids canonical PLT entries (st_shndx=0, st_value!=0). On i386, there are 2 types of PLTs, PIC and non-PIC. Currently, the GCC/GNU as convention is to use R_386_PC32 for non-PIC PLT and R_386_PLT32 for PIC PLT. Copy relocations/canonical PLT entries are possible ABI issues but GCC/GNU as will likely keep the status quo because (1) the ABI is legacy (2) the change will drop a GNU ld diagnostic for non-default visibility ifunc in shared objects. clang-12 -fno-pic (since [1]) can emit R_386_PLT32 for compiler generated function declarations, because preventing canonical PLT entries is weighed over the rare ifunc diagnostic. Further info for the more interested: https://github.com/ClangBuiltLinux/linux/issues/1210 https://sourceware.org/bugzilla/show_bug.cgi?id=27169 https://github.com/llvm/llvm-project/commit/a084c0388e2a59b9556f2de0083333232da3f1d6 [1] [ bp: Massage commit message. ] Reported-by: Arnd Bergmann Signed-off-by: Fangrui Song Signed-off-by: Borislav Petkov Reviewed-by: Nick Desaulniers Reviewed-by: Nathan Chancellor Tested-by: Nick Desaulniers Tested-by: Nathan Chancellor Tested-by: Sedat Dilek Link: https://lkml.kernel.org/r/20210127205600.1227437-1-maskray@google.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/module.c | 1 + arch/x86/tools/relocs.c | 12 ++++++++---- 2 files changed, 9 insertions(+), 4 deletions(-) --- a/arch/x86/kernel/module.c +++ b/arch/x86/kernel/module.c @@ -114,6 +114,7 @@ int apply_relocate(Elf32_Shdr *sechdrs, *location += sym->st_value; break; case R_386_PC32: + case R_386_PLT32: /* Add the value, subtract its position */ *location += sym->st_value - (uint32_t)location; break; --- a/arch/x86/tools/relocs.c +++ b/arch/x86/tools/relocs.c @@ -867,9 +867,11 @@ static int do_reloc32(struct section *se case R_386_PC32: case R_386_PC16: case R_386_PC8: + case R_386_PLT32: /* - * NONE can be ignored and PC relative relocations don't - * need to be adjusted. + * NONE can be ignored and PC relative relocations don't need + * to be adjusted. Because sym must be defined, R_386_PLT32 can + * be treated the same way as R_386_PC32. */ break; @@ -910,9 +912,11 @@ static int do_reloc_real(struct section case R_386_PC32: case R_386_PC16: case R_386_PC8: + case R_386_PLT32: /* - * NONE can be ignored and PC relative relocations don't - * need to be adjusted. + * NONE can be ignored and PC relative relocations don't need + * to be adjusted. Because sym must be defined, R_386_PLT32 can + * be treated the same way as R_386_PC32. */ break;