From 19a6a3acd10e04fc3aba8941b44918acc7003aa2 Mon Sep 17 00:00:00 2001 From: Alan Modra Date: Thu, 26 Mar 2015 12:30:45 +1030 Subject: [PATCH] Harden powerpc64 elf_machine_fixup_plt IFUNC is difficult to correctly implement on any target needing a GOT to support position independent code, due to the dependency on order of dynamic relocations. ld.so should be changed to apply IFUNC relocations last, globally, because without that it is actually impossible to write an IFUNC resolver in C that works in all situations. Case in point, vfork in libpthread.so is an IFUNC with the resolver returning &__libc_vfork. (system and fork are similar.) If another shared library, libA say, uses vfork then it is quite possible that libpthread.so hasn't been dynamically relocated before the unfortunate libA is dynamically relocated. In that case the GOT entry for &__libc_vfork is still zero, so the IFUNC resolver returns NULL. LD_BIND_NOW=1 results in libA PLT dynamic relocations being applied using this NULL value and ld.so segfaults. This patch hardens ld.so to not segfault on a NULL from an IFUNC resolver. It also fixes a problem with undefined weak. If you leave the plt entry as-is for undefined weak then if the entry is ever called it will loop in ld.so rather than segfaulting. * sysdeps/powerpc/powerpc64/dl-machine.h (elf_machine_fixup_plt): Don't segfault if ifunc resolver returns a NULL. Do set plt to zero for undefined weak. (elf_machine_plt_conflict): Similarly. --- ChangeLog | 7 ++++++ sysdeps/powerpc/powerpc64/dl-machine.h | 30 +++++++++++++++++++++----- 2 files changed, 32 insertions(+), 5 deletions(-) diff --git a/ChangeLog b/ChangeLog index 8e159ac507..38ac2ac26c 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,10 @@ +2015-03-26 Alan Modra + + * sysdeps/powerpc/powerpc64/dl-machine.h (elf_machine_fixup_plt): + Don't segfault if ifunc resolver returns a NULL. Do set plt to + zero for undefined weak. + (elf_machine_plt_conflict): Similarly. + 2015-03-25 Joseph Myers * math/auto-libm-test-in: Add more tests of acosh, asinh and diff --git a/sysdeps/powerpc/powerpc64/dl-machine.h b/sysdeps/powerpc/powerpc64/dl-machine.h index 55ac73624b..0576781909 100644 --- a/sysdeps/powerpc/powerpc64/dl-machine.h +++ b/sysdeps/powerpc/powerpc64/dl-machine.h @@ -472,19 +472,32 @@ elf_machine_fixup_plt (struct link_map *map, lookup_t sym_map, Elf64_FuncDesc *plt = (Elf64_FuncDesc *) reloc_addr; Elf64_FuncDesc *rel = (Elf64_FuncDesc *) finaladdr; Elf64_Addr offset = 0; + Elf64_FuncDesc zero_fd = {0, 0, 0}; PPC_DCBT (&plt->fd_aux); PPC_DCBT (&plt->fd_func); - PPC_DCBT (&rel->fd_aux); - PPC_DCBT (&rel->fd_func); - /* If sym_map is NULL, it's a weak undefined sym; Leave the plt zero. */ + /* If sym_map is NULL, it's a weak undefined sym; Set the plt to + zero. finaladdr should be zero already in this case, but guard + against invalid plt relocations with non-zero addends. */ if (sym_map == NULL) - return 0; + finaladdr = 0; + + /* Don't die here if finaladdr is zero, die if this plt entry is + actually called. Makes a difference when LD_BIND_NOW=1. + finaladdr may be zero for a weak undefined symbol, or when an + ifunc resolver returns zero. */ + if (finaladdr == 0) + rel = &zero_fd; + else + { + PPC_DCBT (&rel->fd_aux); + PPC_DCBT (&rel->fd_func); + } /* If the opd entry is not yet relocated (because it's from a shared object that hasn't been processed yet), then manually reloc it. */ - if (map != sym_map && !sym_map->l_relocated + if (finaladdr != 0 && map != sym_map && !sym_map->l_relocated #if !defined RTLD_BOOTSTRAP && defined SHARED /* Bootstrap map doesn't have l_relocated set for it. */ && sym_map != &GL(dl_rtld_map) @@ -522,6 +535,13 @@ elf_machine_plt_conflict (struct link_map *map, lookup_t sym_map, #if _CALL_ELF != 2 Elf64_FuncDesc *plt = (Elf64_FuncDesc *) reloc_addr; Elf64_FuncDesc *rel = (Elf64_FuncDesc *) finaladdr; + Elf64_FuncDesc zero_fd = {0, 0, 0}; + + if (sym_map == NULL) + finaladdr = 0; + + if (finaladdr == 0) + rel = &zero_fd; plt->fd_func = rel->fd_func; plt->fd_aux = rel->fd_aux;