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=-24.0 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, 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 2EFB3C43332 for ; Wed, 24 Feb 2021 13:38:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0797E64ED4 for ; Wed, 24 Feb 2021 13:38:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237241AbhBXNfC (ORCPT ); Wed, 24 Feb 2021 08:35:02 -0500 Received: from mail.kernel.org ([198.145.29.99]:55204 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235505AbhBXM6U (ORCPT ); Wed, 24 Feb 2021 07:58:20 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 647B364F03; Wed, 24 Feb 2021 12:52:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1614171147; bh=PzedoDyaDMMsI/dtCeYqc/Rj7GBfCTq/VNdQzQkdc5g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=P8HT+6XqInnvR41NVNA1dOz5BcGB03aFB0/zjoSOB+6+bxDvI2RGw9zcsQyjtVJf5 iFt/n/JSl3gHtvBm7ZTktiF5SO/fz/Y+kGejoWhoMspue+lmd00cVYOntZD1suox+n rmKnq8ENBBJQqlTrVm4K+nCsG40ng2PWDPPdVafPSJ7btlMTNhMAa76AXrSPdnrB69 OE+sxRrKNimsGKeseHCEKNzZz1IHce2VfK47LYwwvC+DmoLP4vPnlDHSuT9rrt+nUg 4of7z4XPlnexpCBawJKDhus3tLaU6cc5V8jPmiKf7qE17Rbq6Zrjm42Lr/EJ8ffRs5 FuxJuBKG1q1CA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Fangrui Song , Arnd Bergmann , Borislav Petkov , Nick Desaulniers , Nathan Chancellor , Sedat Dilek , Sasha Levin , clang-built-linux@googlegroups.com Subject: [PATCH AUTOSEL 5.10 11/56] x86/build: Treat R_386_PLT32 relocation as R_386_PC32 Date: Wed, 24 Feb 2021 07:51:27 -0500 Message-Id: <20210224125212.482485-11-sashal@kernel.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20210224125212.482485-1-sashal@kernel.org> References: <20210224125212.482485-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Fangrui Song [ Upstream commit bb73d07148c405c293e576b40af37737faf23a6a ] 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: Sasha Levin --- arch/x86/kernel/module.c | 1 + arch/x86/tools/relocs.c | 12 ++++++++---- 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c index 34b153cbd4acb..5e9a34b5bd741 100644 --- 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; diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c index ce7188cbdae58..1c3a1962cade6 100644 --- a/arch/x86/tools/relocs.c +++ b/arch/x86/tools/relocs.c @@ -867,9 +867,11 @@ static int do_reloc32(struct section *sec, Elf_Rel *rel, Elf_Sym *sym, 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 *sec, Elf_Rel *rel, Elf_Sym *sym, 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; -- 2.27.0