From 605338745ba15930e9acac46c32ce6cada12a52b Mon Sep 17 00:00:00 2001 From: Sudakshina Das Date: Mon, 22 Jun 2020 10:57:20 +0100 Subject: aarch64: enable BTI at runtime Binaries can opt-in to using BTI via an ELF object file marking. The dynamic linker has to then mprotect the executable segments with PROT_BTI. In case of static linked executables or in case of the dynamic linker itself, PROT_BTI protection is done by the operating system. On AArch64 glibc uses PT_GNU_PROPERTY instead of PT_NOTE to check the properties of a binary because PT_NOTE can be unreliable with old linkers (old linkers just append the notes of input objects together and add them to the output without checking them for consistency which means multiple incompatible GNU property notes can be present in PT_NOTE). BTI property is handled in the loader even if glibc is not built with BTI support, so in theory user code can be BTI protected independently of glibc. In practice though user binaries are not marked with the BTI property if glibc has no support because the static linked libc objects (crt files, libc_nonshared.a) are unmarked. This patch relies on Linux userspace API that is not yet in a linux release but in v5.8-rc1 so scheduled to be in Linux 5.8. Co-authored-by: Szabolcs Nagy Reviewed-by: Adhemerval Zanella --- sysdeps/aarch64/Makefile | 4 +++ sysdeps/aarch64/dl-bti.c | 54 ++++++++++++++++++++++++++++++++++++++++ sysdeps/aarch64/dl-prop.h | 63 +++++++++++++++++++++++++++++++++++++++++++++++ sysdeps/aarch64/linkmap.h | 3 +++ 4 files changed, 124 insertions(+) create mode 100644 sysdeps/aarch64/dl-bti.c create mode 100644 sysdeps/aarch64/dl-prop.h (limited to 'sysdeps/aarch64') diff --git a/sysdeps/aarch64/Makefile b/sysdeps/aarch64/Makefile index 9cb141004d..5ae8b082b0 100644 --- a/sysdeps/aarch64/Makefile +++ b/sysdeps/aarch64/Makefile @@ -1,5 +1,9 @@ long-double-fcts = yes +ifeq ($(subdir),elf) +sysdep-dl-routines += dl-bti +endif + ifeq ($(subdir),elf) sysdep-dl-routines += tlsdesc dl-tlsdesc gen-as-const-headers += dl-link.sym diff --git a/sysdeps/aarch64/dl-bti.c b/sysdeps/aarch64/dl-bti.c new file mode 100644 index 0000000000..965ddcc732 --- /dev/null +++ b/sysdeps/aarch64/dl-bti.c @@ -0,0 +1,54 @@ +/* AArch64 BTI functions. + Copyright (C) 2020 Free Software Foundation, Inc. + + 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 +#include +#include + +static int +enable_bti (struct link_map *map, const char *program) +{ + const ElfW(Phdr) *phdr; + unsigned prot = PROT_READ | PROT_EXEC | PROT_BTI; + + for (phdr = map->l_phdr; phdr < &map->l_phdr[map->l_phnum]; ++phdr) + if (phdr->p_type == PT_LOAD && (phdr->p_flags & PF_X)) + { + void *start = (void *) (phdr->p_vaddr + map->l_addr); + size_t len = phdr->p_memsz; + if (__mprotect (start, len, prot) < 0) + { + if (program) + _dl_fatal_printf ("%s: mprotect failed to turn on BTI\n", + map->l_name); + else + _dl_signal_error (errno, map->l_name, "dlopen", + N_("mprotect failed to turn on BTI")); + } + } + return 0; +} + +/* Enable BTI for L if required. */ + +void +_dl_bti_check (struct link_map *l, const char *program) +{ + if (GLRO(dl_aarch64_cpu_features).bti && l->l_mach.bti) + enable_bti (l, program); +} diff --git a/sysdeps/aarch64/dl-prop.h b/sysdeps/aarch64/dl-prop.h new file mode 100644 index 0000000000..b0785bda83 --- /dev/null +++ b/sysdeps/aarch64/dl-prop.h @@ -0,0 +1,63 @@ +/* Support for GNU properties. AArch64 version. + Copyright (C) 2018-2020 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 + . */ + +#ifndef _DL_PROP_H +#define _DL_PROP_H + +extern void _dl_bti_check (struct link_map *, const char *) + attribute_hidden; + +static inline void __attribute__ ((always_inline)) +_rtld_main_check (struct link_map *m, const char *program) +{ + _dl_bti_check (m, program); +} + +static inline void __attribute__ ((always_inline)) +_dl_open_check (struct link_map *m) +{ + _dl_bti_check (m, NULL); +} + +static inline void __attribute__ ((always_inline)) +_dl_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph) +{ +} + +static inline int +_dl_process_gnu_property (struct link_map *l, uint32_t type, uint32_t datasz, + void *data) +{ + if (type == GNU_PROPERTY_AARCH64_FEATURE_1_AND) + { + /* Stop if the property note is ill-formed. */ + if (datasz != 4) + return 0; + + unsigned int feature_1 = *(unsigned int *) data; + if (feature_1 & GNU_PROPERTY_AARCH64_FEATURE_1_BTI) + l->l_mach.bti = true; + + /* Stop if we processed the property note. */ + return 0; + } + /* Continue. */ + return 1; +} + +#endif /* _DL_PROP_H */ diff --git a/sysdeps/aarch64/linkmap.h b/sysdeps/aarch64/linkmap.h index 943a9ee9e4..847a03ace2 100644 --- a/sysdeps/aarch64/linkmap.h +++ b/sysdeps/aarch64/linkmap.h @@ -16,8 +16,11 @@ License along with the GNU C Library; if not, see . */ +#include + struct link_map_machine { ElfW(Addr) plt; /* Address of .plt */ void *tlsdesc_table; /* Address of TLS descriptor hash table. */ + bool bti; /* Branch Target Identification is enabled. */ }; -- cgit 1.4.1