From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on starla X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 Received: from server2.sourceware.org (server2.sourceware.org [IPv6:2620:52:3:1:0:246e:9693:128c]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id C04C81F461 for ; Mon, 25 Mar 2024 18:30:18 +0000 (UTC) Authentication-Results: dcvr.yhbt.net; dkim=pass (2048-bit key; unprotected) header.d=efficios.com header.i=@efficios.com header.a=rsa-sha256 header.s=smtpout1 header.b=NHKf0xip; dkim-atps=neutral Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id DAB093858D39 for ; Mon, 25 Mar 2024 18:30:17 +0000 (GMT) Received: from smtpout.efficios.com (smtpout.efficios.com [IPv6:2607:5300:203:b2ee::31e5]) by sourceware.org (Postfix) with ESMTPS id 1862B385840C for ; Mon, 25 Mar 2024 18:29:44 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 1862B385840C Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=efficios.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=efficios.com ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 1862B385840C Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=2607:5300:203:b2ee::31e5 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1711391386; cv=none; b=lzn9kGK+YEHEgqCTUTtlhSiEGPsSI2QnujweY1xBFP8z1oZx6froYCIQZ5xqpYhWxV6QihMli0Y7QXDcTPok3e/ORC8XPkhm1rQ1Vu+rCPMVriSV5ZcIk3/rJtPGVdRgEz7JpaR/XKTzZf9EPyBzc8yoWeF6hiTU4Ri9a89BIYc= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1711391386; c=relaxed/simple; bh=CSnSFnJAggDsM8bO7Bjz632Otg/5hScGGKua/PN2YkU=; h=DKIM-Signature:From:To:Subject:Date:Message-Id:MIME-Version; b=X91O7CTGMkBb0wYgY5/IvZqRi+8xzlbpzNU7VvULcrjuBLyNlIykwDpiVATfBfp211KHYGr3w8mGyLl2YhHLAB/46UcF9x24he9NBFTRUGlcoSDFIxJoAkmOl/nExQme+6p7UNZwwSU6sX9v6cNYc9WdpoR1Ogm9Ds/co+/csnY= ARC-Authentication-Results: i=1; server2.sourceware.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1711391383; bh=CSnSFnJAggDsM8bO7Bjz632Otg/5hScGGKua/PN2YkU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=NHKf0xipYiJsiJymer8CDeFaa2exdK1zESAOanwz6oar3XAxP27GziLwyxLns9TG6 jbykQFKIafDG1W6gXfA0DOVsb9fZyEPEsew9WneY+za99NIekDodhrivaaUzR9V+zY ZR7wsuDL4JqRz+4Ur1oB3IhhfhPB20YsKL4gcYrjRXDKpZTUvHqBlcU0R6K4kiADVi yhETzXBoy9MT+oAzAkUxqNw1tZtQS89nEaZXece6ysLkcwrwhCL6/5e2B40YlRUJzP kM0s/SEQZ2JCuB2ApPFcgVl+HqtkAfqHkZsi4uWfQB1e3u2CBGtYUPS816BJs/xMT7 BU4rd856CI02Q== Received: from laptop-mjeanson.internal.efficios.com (192-222-143-198.qc.cable.ebox.net [192.222.143.198]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4V3M0l4gxHzmvR; Mon, 25 Mar 2024 14:29:43 -0400 (EDT) From: Michael Jeanson To: libc-alpha@sourceware.org Cc: Michael Jeanson , Florian Weimer , Carlos O'Donell , DJ Delorie , Mathieu Desnoyers Subject: [PATCH v10 1/4] nptl: fix potential merge of __rseq_* relro symbols Date: Mon, 25 Mar 2024 14:29:24 -0400 Message-Id: <20240325182927.914830-2-mjeanson@efficios.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240325182927.914830-1-mjeanson@efficios.com> References: <20240325182927.914830-1-mjeanson@efficios.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces+e=80x24.org@sourceware.org While working on a patch to add support for the extensible rseq ABI, we came across an issue where a new 'const' variable would be merged with the existing '__rseq_size' variable. We tracked this to the use of '-fmerge-all-constants' which allows the compiler to merge identical constant variables. This means that all 'const' variables in a compile unit that are of the same size and are initialized to the same value can be merged. In this specific case, on 32 bit systems 'unsigned int' and 'ptrdiff_t' are both 4 bytes and initialized to 0 which should trigger the merge. However for reasons we haven't delved into when the attribute 'section (".data.rel.ro")' is added to the mix, only variables of the same exact types are merged. As far as we know this behavior is not specified anywhere and could change with a new compiler version, hence this patch. Move the definitions of these variables into an assembler file and add hidden writable aliases for internal use. This has the added bonus of removing the asm workaround to set the values on rseq registration. Tested on Debian 12 with GCC 12.2. Signed-off-by: Michael Jeanson Reviewed-by: Mathieu Desnoyers --- Changes sinve v8: - Remove superfluous attributes on externs --- csu/Makefile | 2 +- csu/rseq-sizes.sym | 8 +++++ elf/Makefile | 1 + elf/dl-rseq-symbols.S | 55 +++++++++++++++++++++++++++++++++++ sysdeps/nptl/dl-tls_init_tp.c | 14 ++++----- 5 files changed, 71 insertions(+), 9 deletions(-) create mode 100644 csu/rseq-sizes.sym create mode 100644 elf/dl-rseq-symbols.S diff --git a/csu/Makefile b/csu/Makefile index 946fd91031..948b1aa79e 100644 --- a/csu/Makefile +++ b/csu/Makefile @@ -136,7 +136,7 @@ before-compile += $(objpfx)abi-tag.h generated += abi-tag.h # Put it here to generate it earlier. -gen-as-const-headers += rtld-sizes.sym +gen-as-const-headers += rtld-sizes.sym rseq-sizes.sym # These are the special initializer/finalizer files. They are always the # first and last file in the link. crti.o ... crtn.o define the global diff --git a/csu/rseq-sizes.sym b/csu/rseq-sizes.sym new file mode 100644 index 0000000000..c959758ff0 --- /dev/null +++ b/csu/rseq-sizes.sym @@ -0,0 +1,8 @@ +#include + +-- +RSEQ_SIZE_SIZE sizeof (unsigned int) +RSEQ_SIZE_ALIGN __alignof (unsigned int) + +RSEQ_OFFSET_SIZE sizeof (ptrdiff_t) +RSEQ_OFFSET_ALIGN __alignof (ptrdiff_t) diff --git a/elf/Makefile b/elf/Makefile index 4f1903391a..1019e3e2dd 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -73,6 +73,7 @@ dl-routines = \ dl-origin \ dl-printf \ dl-reloc \ + dl-rseq-symbols \ dl-runtime \ dl-scope \ dl-setup_hash \ diff --git a/elf/dl-rseq-symbols.S b/elf/dl-rseq-symbols.S new file mode 100644 index 0000000000..2d8e88367f --- /dev/null +++ b/elf/dl-rseq-symbols.S @@ -0,0 +1,55 @@ +/* Define symbols used by rseq. + Copyright (C) 2024 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 +#include + +/* Some targets define a macro to denote the zero register. */ +#undef zero + +/* Define 2 symbols, __rseq_size is public const and _rseq_size, which is an + alias of __rseq_size, but hidden and writable for internal use. */ + + .globl __rseq_size + .type __rseq_size, %object + .size __rseq_size, RSEQ_SIZE_SIZE + .hidden _rseq_size + .globl _rseq_size + .type _rseq_size, %object + .size _rseq_size, RSEQ_SIZE_SIZE + .section .data.rel.ro + .balign RSEQ_SIZE_ALIGN +__rseq_size: +_rseq_size: + .zero RSEQ_SIZE_SIZE + +/* Define 2 symbols, __rseq_offset is public const and _rseq_offset, which is an + alias of __rseq_offset, but hidden and writable for internal use. */ + + .globl __rseq_offset + .type __rseq_offset, %object + .size __rseq_offset, RSEQ_OFFSET_SIZE + .hidden _rseq_offset + .globl _rseq_offset + .type _rseq_offset, %object + .size _rseq_offset, RSEQ_OFFSET_SIZE + .section .data.rel.ro + .balign RSEQ_OFFSET_ALIGN +__rseq_offset: +_rseq_offset: + .zero RSEQ_OFFSET_SIZE diff --git a/sysdeps/nptl/dl-tls_init_tp.c b/sysdeps/nptl/dl-tls_init_tp.c index 092c274f36..2f9750c50b 100644 --- a/sysdeps/nptl/dl-tls_init_tp.c +++ b/sysdeps/nptl/dl-tls_init_tp.c @@ -45,8 +45,10 @@ rtld_mutex_dummy (pthread_mutex_t *lock) #endif const unsigned int __rseq_flags; -const unsigned int __rseq_size attribute_relro; -const ptrdiff_t __rseq_offset attribute_relro; + +/* The variables are in .data.relro but are not yet write-protected. */ +extern unsigned int _rseq_size; +extern ptrdiff_t _rseq_offset; void __tls_pre_init_tp (void) @@ -105,10 +107,7 @@ __tls_init_tp (void) do_rseq = TUNABLE_GET (rseq, int, NULL); if (rseq_register_current_thread (pd, do_rseq)) { - /* We need a writable view of the variables. They are in - .data.relro and are not yet write-protected. */ - extern unsigned int size __asm__ ("__rseq_size"); - size = sizeof (pd->rseq_area); + _rseq_size = sizeof (pd->rseq_area); } #ifdef RSEQ_SIG @@ -117,8 +116,7 @@ __tls_init_tp (void) all targets support __thread_pointer, so set __rseq_offset only if the rseq registration may have happened because RSEQ_SIG is defined. */ - extern ptrdiff_t offset __asm__ ("__rseq_offset"); - offset = (char *) &pd->rseq_area - (char *) __thread_pointer (); + _rseq_offset = (char *) &pd->rseq_area - (char *) __thread_pointer (); #endif } -- 2.34.1