From 5474d94f03aedba2f832006dc7d680cc15792a7b Mon Sep 17 00:00:00 2001 From: Alan Modra Date: Mon, 26 Dec 2016 00:30:45 +1030 Subject: dynrelro section for read-only dynamic symbols copied into executable Variables defined in shared libraries are copied into an executable's .bss section when code in the executable is non-PIC and thus would require dynamic text relocations to access the variable directly in the shared library. Recent x86 toolchains also copy variables into the executable to gain a small speed improvement. The problem is that if the variable was originally read-only, the copy in .bss is writable, potentially opening a security hole. This patch cures that problem by putting the copy in a section that becomes read-only after ld.so relocation, provided -z relro is in force. The patch also fixes a microblaze linker segfault on attempting to use dynamic bss variables. bfd/ PR ld/20995 * elf-bfd.h (struct elf_link_hash_table): Add sdynrelro and sreldynrelro. (struct elf_backend_data): Add want_dynrelro. * elfxx-target.h (elf_backend_want_dynrelro): Define. (elfNN_bed): Update initializer. * elflink.c (_bfd_elf_create_dynamic_sections): Create sdynrelro and sreldynrelro sections. * elf32-arm.c (elf32_arm_adjust_dynamic_symbol): Place variables copied into the executable from read-only sections into sdynrelro. (elf32_arm_size_dynamic_sections): Handle sdynrelro. (elf32_arm_finish_dynamic_symbol): Select sreldynrelro for dynamic relocs in sdynrelro. (elf_backend_want_dynrelro): Define. * elf32-hppa.c (elf32_hppa_adjust_dynamic_symbol) (elf32_hppa_size_dynamic_sections, elf32_hppa_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elf32-i386.c (elf_i386_adjust_dynamic_symbol) (elf_i386_size_dynamic_sections, elf_i386_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elf32-metag.c (elf_metag_adjust_dynamic_symbol) (elf_metag_size_dynamic_sections, elf_metag_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elf32-microblaze.c (microblaze_elf_adjust_dynamic_symbol) (microblaze_elf_size_dynamic_sections) (microblaze_elf_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elf32-nios2.c (nios2_elf32_finish_dynamic_symbol) (nios2_elf32_adjust_dynamic_symbol) (nios2_elf32_size_dynamic_sections) (elf_backend_want_dynrelro): As above. * elf32-or1k.c (or1k_elf_finish_dynamic_symbol) (or1k_elf_adjust_dynamic_symbol, or1k_elf_size_dynamic_sections) (elf_backend_want_dynrelro): As above. * elf32-ppc.c (ppc_elf_adjust_dynamic_symbol) (ppc_elf_size_dynamic_sections, ppc_elf_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elf32-s390.c (elf_s390_adjust_dynamic_symbol) (elf_s390_size_dynamic_sections, elf_s390_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elf32-tic6x.c (elf32_tic6x_adjust_dynamic_symbol) (elf32_tic6x_size_dynamic_sections) (elf32_tic6x_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elf32-tilepro.c (tilepro_elf_adjust_dynamic_symbol) (tilepro_elf_size_dynamic_sections) (tilepro_elf_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elf64-ppc.c (ppc64_elf_adjust_dynamic_symbol) (ppc64_elf_size_dynamic_sections, ppc64_elf_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elf64-s390.c (elf_s390_adjust_dynamic_symbol) (elf_s390_size_dynamic_sections, elf_s390_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elf64-x86-64.c (elf_x86_64_adjust_dynamic_symbol) (elf_x86_64_size_dynamic_sections) (elf_x86_64_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elfnn-aarch64.c (elfNN_aarch64_adjust_dynamic_symbol) (elfNN_aarch64_size_dynamic_sections) (elfNN_aarch64_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elfnn-riscv.c (riscv_elf_adjust_dynamic_symbol) (riscv_elf_size_dynamic_sections, riscv_elf_finish_dynamic_symbol) (elf_backend_want_dynrelro): As above. * elfxx-mips.c (_bfd_mips_elf_adjust_dynamic_symbol) (_bfd_mips_elf_size_dynamic_sections) (_bfd_mips_vxworks_finish_dynamic_symbol): As above. * elfxx-sparc.c (_bfd_sparc_elf_adjust_dynamic_symbol) (_bfd_sparc_elf_size_dynamic_sections) (_bfd_sparc_elf_finish_dynamic_symbol): As above. * elfxx-tilegx.c (tilegx_elf_adjust_dynamic_symbol) (tilegx_elf_size_dynamic_sections) (tilegx_elf_finish_dynamic_symbol): As above. * elf32-mips.c (elf_backend_want_dynrelro): Define. * elf64-mips.c (elf_backend_want_dynrelro): Define. * elf32-sparc.c (elf_backend_want_dynrelro): Define. * elf64-sparc.c (elf_backend_want_dynrelro): Define. * elf32-tilegx.c (elf_backend_want_dynrelro): Define. * elf64-tilegx.c (elf_backend_want_dynrelro): Define. * elf32-microblaze.c (microblaze_elf_adjust_dynamic_symbol): Tidy. (microblaze_elf_size_dynamic_sections): Handle sdynbss. * elf32-nios2.c (nios2_elf32_size_dynamic_sections): Make use of linker shortcuts to dynamic sections rather than comparing names. Correctly set "got" flag. ld/ PR ld/20995 * testsuite/ld-arm/farcall-mixed-app-v5.d: Update to suit changed stub hash table traversal caused by section id increment. Accept the previous output too. * testsuite/ld-arm/farcall-mixed-app.d: Likewise. * testsuite/ld-arm/farcall-mixed-lib-v4t.d: Likewise. * testsuite/ld-arm/farcall-mixed-lib.d: Likewise. * testsuite/ld-elf/pr20995a.s, * testsuite/ld-elf/pr20995b.s, * testsuite/ld-elf/pr20995.r: New test. * testsuite/ld-elf/elf.exp: Run it. --- bfd/elf-bfd.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'bfd/elf-bfd.h') diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h index 4093434e64..1c634d8dd1 100644 --- a/bfd/elf-bfd.h +++ b/bfd/elf-bfd.h @@ -597,6 +597,8 @@ struct elf_link_hash_table asection *srelplt; asection *sdynbss; asection *srelbss; + asection *sdynrelro; + asection *sreldynrelro; asection *igotplt; asection *iplt; asection *irelplt; @@ -1451,6 +1453,7 @@ struct elf_backend_data unsigned can_refcount : 1; unsigned want_got_sym : 1; unsigned want_dynbss : 1; + unsigned want_dynrelro : 1; /* Targets which do not support physical addressing often require that the p_paddr field in the section header to be set to zero. -- cgit v1.2.3