From patchwork Wed Jun 1 17:56:33 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fangrui Song X-Patchwork-Id: 54689 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id B26A5384B0C9 for ; Wed, 1 Jun 2022 17:57:02 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org B26A5384B0C9 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1654106222; bh=p3bUqc5x/rz39ODE76BeUroSqSoXgLU2eQEIuGbHmNA=; h=Date:In-Reply-To:References:Subject:To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To: From; b=svePlVXs7Y9klGucQBlRiYy0QN7gl8v+nmcZaN8gYmHEDICk2lp1nw1ddEUEeam+3 RbM3nx70/TaYWkmfn+C2VC0BkNUjfTX+wNCgmFPdNnKLsTsuOWOvO7OsWlMjZUvC7r Q+vMje2gZj1Kcgqn7wlm3B4n0f0pTsH/S1I4K4a4= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by sourceware.org (Postfix) with ESMTPS id 643AB3856DD4 for ; Wed, 1 Jun 2022 17:56:40 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 643AB3856DD4 Received: by mail-yb1-xb49.google.com with SMTP id n3-20020a257203000000b0064f867fcfc0so2021239ybc.15 for ; Wed, 01 Jun 2022 10:56:40 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=p3bUqc5x/rz39ODE76BeUroSqSoXgLU2eQEIuGbHmNA=; b=b8kdwVoiWZ03CsYx7OEWFFAhwp7a39cDsPTatZr2cuabxEOlVJrjrA2kssa3JGld4c AlACOjoALswqg3juhsQtSnLl5YTv1baW9jjE3rtDF/qilszyzZdrs4Cr27mIz1nzxr23 AU7gkR9+piQ1qOgwKgcS3ww+G9bFLHt6hUBBOWK9xn6y91NX8Qb4+BUWTLDQnx6WvnwS ZUAOj/wSCcshcWlnEb1vRQuA4k4s4z628R5vqBJS0vLK0O7EehlyAm+mtHT/vAyJ/B49 76oohXq8U8uB7TwaUoANeBAqaq3fVkkygNkt+2832MqbbjVHgVZH5Fv/7vTSCJnRpa95 TSQA== X-Gm-Message-State: AOAM532MyUTaM/ZD9fyfXY9q4Vx1oQZEQgk3vI5pd7WnURU0tpCpLkrP UvcpmrT4Zbyi2TVHEP62j7zW038xtSpTC8rjKPicipZwd5xIXsdhPMUK4UZIGyWxpgR4lvQW9Hd Yv8BjULSL18018F0fSuD0MsfHj7odNTAEv7KqE6wX8eYtyw0DaxF+ZACvvs/KzcKzVY8a X-Google-Smtp-Source: ABdhPJy9gNzT9jujWArhAqQoQY01p9z+PdNDanXHyMj1f0vaoIj79ZKMhog7uXIEnXIQHE9oC0E9+jrN04Mz X-Received: from maskray1.svl.corp.google.com ([2620:15c:2ce:200:d5a8:eb1:a3e6:329f]) (user=maskray job=sendgmr) by 2002:a25:6583:0:b0:660:3a01:84f7 with SMTP id z125-20020a256583000000b006603a0184f7mr986717ybb.130.1654106199669; Wed, 01 Jun 2022 10:56:39 -0700 (PDT) Date: Wed, 1 Jun 2022 10:56:33 -0700 In-Reply-To: Message-Id: <20220601175633.2407189-1-maskray@google.com> Mime-Version: 1.0 References: Subject: [PATCH v3] elf: Remove ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA To: libc-alpha@sourceware.org, Szabolcs Nagy X-Spam-Status: No, score=-19.9 required=5.0 tests=BAYES_00, DKIMWL_WL_MED, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE, USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Fangrui Song via Libc-alpha From: Fangrui Song Reply-To: Fangrui Song Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" If an executable has copy relocations for extern protected data, that can only work if the library containing the definition is built with assumptions (a) the compiler emits GOT-generating relocations (b) the linker produces R_*_GLOB_DAT instead of R_*_RELATIVE. Otherwise the library uses its own definition directly and the executable accesses a stale copy. Note: the GOT relocations defeat the purpose of protected visibility as an optimization, but allow rtld to make the executable and library use the same copy when copy relocations are present, but it turns out this never worked perfectly. ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA has strange semantics when both a.so and b.so define protected var and the executable copy relocates var: b.so accesses its own copy even with GLOB_DAT. The behavior change is from commit 62da1e3b00b51383ffa7efc89d8addda0502e107 (x86) and then copied to nios2 (ae5eae7cfc9c4a8297ff82ec6b794faca1976ecc) and arc (0e7d930c4c11de896fe807f67fa1eb756c9c1e05). Without ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA, b.so accesses the copy relocated data like a.so. ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA has another effect in the absence of copy relocations: when a protected data symbol is defined in multiple objects, the code tries to bind the relocation locally. Without ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA, STV_PROTECTED is handled in the same way as STV_DEFAULT: if ld produces GLOB_DAT (some ports of GNU ld), the relocation will bind to the first definition; otherwise (e.g. ld.lld) ld does the binding locally and ld.so doesn't help. It's extremely unlikely anyone relies on the ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA behavior, so let's remove it: this removes a check in the symbol lookup code. --- Changes from v1: * Reword commit message as suggested by Szabolcs Nagy Changes from v2: * Explain interposition behavior --- elf/dl-lookup.c | 90 ------------------------------------- sysdeps/arc/dl-sysdep.h | 21 --------- sysdeps/generic/ldsodefs.h | 12 +---- sysdeps/i386/dl-machine.h | 3 +- sysdeps/nios2/dl-sysdep.h | 21 --------- sysdeps/x86/dl-lookupcfg.h | 4 -- sysdeps/x86_64/dl-machine.h | 8 +--- 7 files changed, 4 insertions(+), 155 deletions(-) delete mode 100644 sysdeps/arc/dl-sysdep.h delete mode 100644 sysdeps/nios2/dl-sysdep.h diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c index a42f6d5390..41d108e0b8 100644 --- a/elf/dl-lookup.c +++ b/elf/dl-lookup.c @@ -456,59 +456,6 @@ do_lookup_x (const char *undef_name, unsigned int new_hash, if (sym != NULL) { found_it: - /* When UNDEF_MAP is NULL, which indicates we are called from - do_lookup_x on relocation against protected data, we skip - the data definion in the executable from copy reloc. */ - if (ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA - && undef_map == NULL - && map->l_type == lt_executable - && type_class == ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA) - { - const ElfW(Sym) *s; - unsigned int i; - -#if ! ELF_MACHINE_NO_RELA - if (map->l_info[DT_RELA] != NULL - && map->l_info[DT_RELASZ] != NULL - && map->l_info[DT_RELASZ]->d_un.d_val != 0) - { - const ElfW(Rela) *rela - = (const ElfW(Rela) *) D_PTR (map, l_info[DT_RELA]); - unsigned int rela_count - = map->l_info[DT_RELASZ]->d_un.d_val / sizeof (*rela); - - for (i = 0; i < rela_count; i++, rela++) - if (elf_machine_type_class (ELFW(R_TYPE) (rela->r_info)) - == ELF_RTYPE_CLASS_COPY) - { - s = &symtab[ELFW(R_SYM) (rela->r_info)]; - if (!strcmp (strtab + s->st_name, undef_name)) - goto skip; - } - } -#endif -#if ! ELF_MACHINE_NO_REL - if (map->l_info[DT_REL] != NULL - && map->l_info[DT_RELSZ] != NULL - && map->l_info[DT_RELSZ]->d_un.d_val != 0) - { - const ElfW(Rel) *rel - = (const ElfW(Rel) *) D_PTR (map, l_info[DT_REL]); - unsigned int rel_count - = map->l_info[DT_RELSZ]->d_un.d_val / sizeof (*rel); - - for (i = 0; i < rel_count; i++, rel++) - if (elf_machine_type_class (ELFW(R_TYPE) (rel->r_info)) - == ELF_RTYPE_CLASS_COPY) - { - s = &symtab[ELFW(R_SYM) (rel->r_info)]; - if (!strcmp (strtab + s->st_name, undef_name)) - goto skip; - } - } -#endif - } - /* Hidden and internal symbols are local, ignore them. */ if (__glibc_unlikely (dl_symbol_visibility_binds_local_p (sym))) goto skip; @@ -854,43 +801,6 @@ _dl_lookup_symbol_x (const char *undef_name, struct link_map *undef_map, return 0; } - int protected = (*ref - && ELFW(ST_VISIBILITY) ((*ref)->st_other) == STV_PROTECTED); - if (__glibc_unlikely (protected != 0)) - { - /* It is very tricky. We need to figure out what value to - return for the protected symbol. */ - if (type_class == ELF_RTYPE_CLASS_PLT) - { - if (current_value.s != NULL && current_value.m != undef_map) - { - current_value.s = *ref; - current_value.m = undef_map; - } - } - else - { - struct sym_val protected_value = { NULL, NULL }; - - for (scope = symbol_scope; *scope != NULL; i = 0, ++scope) - if (do_lookup_x (undef_name, new_hash, &old_hash, *ref, - &protected_value, *scope, i, version, flags, - skip_map, - (ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA - && ELFW(ST_TYPE) ((*ref)->st_info) == STT_OBJECT - && type_class == ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA) - ? ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA - : ELF_RTYPE_CLASS_PLT, NULL) != 0) - break; - - if (protected_value.s != NULL && protected_value.m != undef_map) - { - current_value.s = *ref; - current_value.m = undef_map; - } - } - } - /* We have to check whether this would bind UNDEF_MAP to an object in the global scope which was dynamically loaded. In this case we have to prevent the latter from being unloaded unless the diff --git a/sysdeps/arc/dl-sysdep.h b/sysdeps/arc/dl-sysdep.h deleted file mode 100644 index cf4d160a73..0000000000 --- a/sysdeps/arc/dl-sysdep.h +++ /dev/null @@ -1,21 +0,0 @@ -/* System-specific settings for dynamic linker code. ARC version. - Copyright (C) 2020-2022 Free Software Foundation, Inc. - This file is part of the GNU C Library. - - The GNU C Library is free software; you can redistribute it and/or - modify it under the terms of the GNU Lesser General Public - License as published by the Free Software Foundation; either - version 2.1 of the License, or (at your option) any later version. - - The GNU C Library is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - Lesser General Public License for more details. - - You should have received a copy of the GNU Lesser General Public - License along with the GNU C Library. If not, see - . */ - -#include_next - -#define DL_EXTERN_PROTECTED_DATA diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h index 6716e1f382..d3cbfd4f95 100644 --- a/sysdeps/generic/ldsodefs.h +++ b/sysdeps/generic/ldsodefs.h @@ -149,23 +149,13 @@ dl_symbol_visibility_binds_local_p (const ElfW(Sym) *sym) satisfied by any symbol in the executable. Some architectures do not support copy relocations. In this case we define the macro to zero so that the code for handling them gets automatically optimized - out. ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA means address of protected - data defined in the shared library may be external, i.e., due to copy - relocation. */ + out. */ #define ELF_RTYPE_CLASS_PLT 1 #ifndef DL_NO_COPY_RELOCS # define ELF_RTYPE_CLASS_COPY 2 #else # define ELF_RTYPE_CLASS_COPY 0 #endif -/* If DL_EXTERN_PROTECTED_DATA is defined, address of protected data - defined in the shared library may be external, i.e., due to copy - relocation. */ -#ifdef DL_EXTERN_PROTECTED_DATA -# define ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA 4 -#else -# define ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA 0 -#endif /* ELF uses the PF_x macros to specify the segment permissions, mmap uses PROT_xxx. In most cases the three macros have the values 1, 2, diff --git a/sysdeps/i386/dl-machine.h b/sysdeps/i386/dl-machine.h index 1f8d734215..3311631a3e 100644 --- a/sysdeps/i386/dl-machine.h +++ b/sysdeps/i386/dl-machine.h @@ -203,8 +203,7 @@ _dl_start_user:\n\ || (type) == R_386_TLS_DTPOFF32 || (type) == R_386_TLS_TPOFF32 \ || (type) == R_386_TLS_TPOFF || (type) == R_386_TLS_DESC) \ * ELF_RTYPE_CLASS_PLT) \ - | (((type) == R_386_COPY) * ELF_RTYPE_CLASS_COPY) \ - | (((type) == R_386_GLOB_DAT) * ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA)) + | (((type) == R_386_COPY) * ELF_RTYPE_CLASS_COPY)) /* A reloc type used for ld.so cmdline arg lookups to reject PLT entries. */ #define ELF_MACHINE_JMP_SLOT R_386_JMP_SLOT diff --git a/sysdeps/nios2/dl-sysdep.h b/sysdeps/nios2/dl-sysdep.h deleted file mode 100644 index 257b37c258..0000000000 --- a/sysdeps/nios2/dl-sysdep.h +++ /dev/null @@ -1,21 +0,0 @@ -/* System-specific settings for dynamic linker code. Nios II version. - Copyright (C) 2009-2022 Free Software Foundation, Inc. - This file is part of the GNU C Library. - - The GNU C Library is free software; you can redistribute it and/or - modify it under the terms of the GNU Lesser General Public - License as published by the Free Software Foundation; either - version 2.1 of the License, or (at your option) any later version. - - The GNU C Library is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - Lesser General Public License for more details. - - You should have received a copy of the GNU Lesser General Public - License along with the GNU C Library. If not, see - . */ - -#include_next - -#define DL_EXTERN_PROTECTED_DATA diff --git a/sysdeps/x86/dl-lookupcfg.h b/sysdeps/x86/dl-lookupcfg.h index 18b3b49f6e..e136cc63af 100644 --- a/sysdeps/x86/dl-lookupcfg.h +++ b/sysdeps/x86/dl-lookupcfg.h @@ -20,10 +20,6 @@ #include_next -/* Address of protected data defined in the shared library may be - external due to copy relocation. */ -#define DL_EXTERN_PROTECTED_DATA - struct link_map; extern void _dl_unmap (struct link_map *map) attribute_hidden; diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h index 7f607f6dff..78aecfc9fd 100644 --- a/sysdeps/x86_64/dl-machine.h +++ b/sysdeps/x86_64/dl-machine.h @@ -181,10 +181,7 @@ _dl_start_user:\n\ TLS variable, so undefined references should not be allowed to define the value. ELF_RTYPE_CLASS_COPY iff TYPE should not be allowed to resolve to one - of the main executable's symbols, as for a COPY reloc. - ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA iff TYPE describes relocation may - against protected data whose address be external due to copy relocation. - */ + of the main executable's symbols, as for a COPY reloc. */ #define elf_machine_type_class(type) \ ((((type) == R_X86_64_JUMP_SLOT \ || (type) == R_X86_64_DTPMOD64 \ @@ -192,8 +189,7 @@ _dl_start_user:\n\ || (type) == R_X86_64_TPOFF64 \ || (type) == R_X86_64_TLSDESC) \ * ELF_RTYPE_CLASS_PLT) \ - | (((type) == R_X86_64_COPY) * ELF_RTYPE_CLASS_COPY) \ - | (((type) == R_X86_64_GLOB_DAT) * ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA)) + | (((type) == R_X86_64_COPY) * ELF_RTYPE_CLASS_COPY)) /* A reloc type used for ld.so cmdline arg lookups to reject PLT entries. */ #define ELF_MACHINE_JMP_SLOT R_X86_64_JUMP_SLOT