diff options
Diffstat (limited to '0002-nptl-fix-potential-merge-of-__rseq_-relro-symbols.patch')
| -rw-r--r-- | 0002-nptl-fix-potential-merge-of-__rseq_-relro-symbols.patch | 161 |
1 files changed, 161 insertions, 0 deletions
diff --git a/0002-nptl-fix-potential-merge-of-__rseq_-relro-symbols.patch b/0002-nptl-fix-potential-merge-of-__rseq_-relro-symbols.patch new file mode 100644 index 0000000..f393800 --- /dev/null +++ b/0002-nptl-fix-potential-merge-of-__rseq_-relro-symbols.patch @@ -0,0 +1,161 @@ +From 7bfc35959dae3287e9097a960ebfddb19441bb55 Mon Sep 17 00:00:00 2001 +From: Michael Jeanson <mjeanson@efficios.com> +Date: Wed, 3 Jul 2024 12:35:34 -0400 +Subject: [PATCH 02/12] nptl: fix potential merge of __rseq_* relro symbols + +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 <mjeanson@efficios.com> +Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> +Reviewed-by: Florian Weimer <fweimer@redhat.com> +(cherry picked from commit 2b92982e2369d292560793bee8e730f695f48ff3) +--- + elf/Makefile | 1 + + elf/dl-rseq-symbols.S | 64 +++++++++++++++++++++++++++++++++++ + sysdeps/nptl/dl-tls_init_tp.c | 14 ++++---- + 3 files changed, 71 insertions(+), 8 deletions(-) + create mode 100644 elf/dl-rseq-symbols.S + +diff --git a/elf/Makefile b/elf/Makefile +index c2af11b92c..04e1d7ded5 100644 +--- a/elf/Makefile ++++ b/elf/Makefile +@@ -74,6 +74,7 @@ dl-routines = \ + dl-printf \ + dl-profile \ + 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..b4bba06a99 +--- /dev/null ++++ b/elf/dl-rseq-symbols.S +@@ -0,0 +1,64 @@ ++/* 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 ++ <https://www.gnu.org/licenses/>. */ ++ ++#include <sysdep.h> ++ ++#if __WORDSIZE == 64 ++#define RSEQ_OFFSET_SIZE 8 ++#else ++#define RSEQ_OFFSET_SIZE 4 ++#endif ++ ++/* Some targets define a macro to denote the zero register. */ ++#undef zero ++ ++/* Define 2 symbols: '__rseq_size' is public const and '_rseq_size' (an ++ alias of '__rseq_size') is hidden and writable for internal use by the ++ dynamic linker which will initialize the value both symbols point to ++ before copy relocations take place. */ ++ ++ .globl __rseq_size ++ .type __rseq_size, %object ++ .size __rseq_size, 4 ++ .hidden _rseq_size ++ .globl _rseq_size ++ .type _rseq_size, %object ++ .size _rseq_size, 4 ++ .section .data.rel.ro ++ .balign 4 ++__rseq_size: ++_rseq_size: ++ .zero 4 ++ ++/* Define 2 symbols: '__rseq_offset' is public const and '_rseq_offset' (an ++ alias of '__rseq_offset') is hidden and writable for internal use by the ++ dynamic linker which will initialize the value both symbols point to ++ before copy relocations take place. */ ++ ++ .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_SIZE ++__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 2ed98c5a31..45ae260ceb 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 attribute_hidden; ++extern ptrdiff_t _rseq_offset attribute_hidden; + + 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 + } + +-- +2.33.0 + |