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Richte" , Fangrui Song Subject: [PATCH] Fix ifunc support with DT_TEXTREL segments (BZ#20480) Date: Thu, 30 Aug 2018 17:07:24 -0300 Message-Id: <20180830200724.30045-1-adhemerval.zanella@linaro.org> Currently, DT_TEXTREL is incompatible with IFUNC. When DT_TEXTREL or DF_TEXTREL is seen, the dynamic linker calls __mprotect on the segments with PROT_READ|PROT_WRITE before applying dynamic relocations. It leads to segfault when performing IFUNC resolution (which requires PROT_EXEC as well for the IFUNC resolver). This patch makes it call __mprotect with extra PROT_WRITE bit, which will keep the PROT_EXEC bit if exists, and thus fixes the segfault. FreeBSD rtld libexec/rtld-elf/rtld.c (reloc_textrel_prot) does the same. Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu, sparc64-linux-gnu, sparcv9-linux-gnu, and armv8-linux-gnueabihf. Adam J. Richte Adhemerval Zanella Fangrui Song [BZ #20480] * config.h.in (CAN_TEXTREL_IFUNC): New define. * configure.ac: Add check if linker supports textrel relocation with ifunc. * elf/dl-reloc.c (_dl_relocate_object): Use all required flags on DT_TEXTREL segments, not only PROT_READ and PROT_WRITE. * elf/Makefile (ifunc-pie-tests): Add tst-ifunc-textrel. (CFLAGS-tst-ifunc-textrel.c): New rule. * elf/tst-ifunc-textrel.c: New file. --- ChangeLog | 14 +++++++++++ config.h.in | 3 +++ configure | 51 +++++++++++++++++++++++++++++++++++++++ configure.ac | 38 +++++++++++++++++++++++++++++ elf/Makefile | 4 +++- elf/dl-reloc.c | 20 +++++++--------- elf/tst-ifunc-textrel.c | 53 +++++++++++++++++++++++++++++++++++++++++ 7 files changed, 170 insertions(+), 13 deletions(-) create mode 100644 elf/tst-ifunc-textrel.c -- 2.17.1 diff --git a/config.h.in b/config.h.in index 141db213a9..d6fcbbac78 100644 --- a/config.h.in +++ b/config.h.in @@ -247,4 +247,7 @@ in i386 6 argument syscall issue). */ #define CAN_USE_REGISTER_ASM_EBP 0 +/* Linker supports ifunc with text relocation (used in tests). */ +#define CAN_TEXTREL_IFUNC 0 + #endif diff --git a/configure b/configure index 285a6537f0..ab4c12c5ba 100755 --- a/configure +++ b/configure @@ -664,6 +664,7 @@ INSTALL_PROGRAM sysnames submachine multi_arch +libc_cv_textrel_ifunc no_stack_protector stack_protector libc_cv_ssp @@ -4052,6 +4053,56 @@ fi { $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_indirect_function" >&5 $as_echo "$libc_cv_gcc_indirect_function" >&6; } +# Check if linker supports textrel relocation with ifunc (used on elf/tests). +# Note that it relies on libc_cv_ld_gnu_indirect_function test above. +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the linker supports textrels along with ifunc" >&5 +$as_echo_n "checking whether the linker supports textrels along with ifunc... " >&6; } +if ${libc_cv_textrel_ifunc+:} false; then : + $as_echo_n "(cached) " >&6 +else + cat > conftest.S <&5 + (eval $ac_try) 2>&5 + ac_status=$? + $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5 + test $ac_status = 0; }; }; then + libc_cv_textrel_ifunc=yes + fi +fi +rm -f conftest* +fi +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_textrel_ifunc" >&5 +$as_echo "$libc_cv_textrel_ifunc" >&6; } +if test $libc_cv_textrel_ifunc = yes; then + $as_echo "#define CAN_TEXTREL_IFUNC 1" >>confdefs.h + +fi + + # Check if gcc warns about alias for function with incompatible types. { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5 $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; } diff --git a/configure.ac b/configure.ac index 8045d44dd0..e3d5c0598b 100644 --- a/configure.ac +++ b/configure.ac @@ -671,6 +671,44 @@ if ${CC-cc} -c conftest.c -o conftest.o 1>&AS_MESSAGE_LOG_FD \ fi rm -f conftest*]) +# Check if linker supports textrel relocation with ifunc (used on elf/tests). +# Note that it relies on libc_cv_ld_gnu_indirect_function test above. +AC_CACHE_CHECK([whether the linker supports textrels along with ifunc], + libc_cv_textrel_ifunc, [dnl +cat > conftest.S <start = PTR_ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize)) + (caddr_t) l->l_addr; - if (__mprotect (newp->start, newp->len, PROT_READ|PROT_WRITE) < 0) - { - errstring = N_("cannot make segment writable for relocation"); - call_error: - _dl_signal_error (errno, l->l_name, NULL, errstring); - } - -#if (PF_R | PF_W | PF_X) == 7 && (PROT_READ | PROT_WRITE | PROT_EXEC) == 7 - newp->prot = (PF_TO_PROT - >> ((ph->p_flags & (PF_R | PF_W | PF_X)) * 4)) & 0xf; -#else newp->prot = 0; if (ph->p_flags & PF_R) newp->prot |= PROT_READ; @@ -218,7 +207,14 @@ _dl_relocate_object (struct link_map *l, struct r_scope_elem *scope[], newp->prot |= PROT_WRITE; if (ph->p_flags & PF_X) newp->prot |= PROT_EXEC; -#endif + + if (__mprotect (newp->start, newp->len, newp->prot|PROT_WRITE) < 0) + { + errstring = N_("cannot make segment writable for relocation"); + call_error: + _dl_signal_error (errno, l->l_name, NULL, errstring); + } + newp->next = textrels; textrels = newp; } diff --git a/elf/tst-ifunc-textrel.c b/elf/tst-ifunc-textrel.c new file mode 100644 index 0000000000..60e5ac3bf8 --- /dev/null +++ b/elf/tst-ifunc-textrel.c @@ -0,0 +1,53 @@ +/* Check DT_TEXTREL/DF_TEXTREL support with ifunc. + Copyright (C) 2018 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 + +/* Some linkers may fail to produce a shared object with ifunc and text + relocations. */ +#if CAN_TEXTREL_IFUNC +/* Force a text relocation in the object. */ +static const uintptr_t +address __attribute__((section(".text"))) = (uintptr_t) &address; + +static uintptr_t +foo_impl (void) +{ + return address; +} + +void * +__attribute__((noinline)) +foo (void) +{ + return (void*) foo_impl; +} +__asm__ (".type foo, %gnu_indirect_function"); +#endif + +static int +do_test (void) +{ +#if CAN_TEXTREL_IFUNC + return (uintptr_t) foo () != 0 ? 0 : 1; +#else + return 0; +#endif +} + +#include