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). A new _dl_process_pt_gnu_property
hook is introduced in dl-prop.h and to keep it maintainable the
rtld and dlopen code paths use the same function (if the main
map needs special treatment, that should be inferred by the hook
from the link map). Unlike the _dt_process_pt_note hook this one
is called after segments are mapped to avoid unbounded allocation
and additional read syscall. Otherwise the AArch64 logic follows
the x86 logic for handling GNU properties (but the code is not
shared because x86 needs to manage internal CET state and look
out for multiple property notes).
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 scheduled to be
merged in Linux 5.8 and now it is in the for-next/bti-user branch
of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git.
Co-authored-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
maplength, has_holes, loader);
if (__glibc_unlikely (errstring != NULL))
goto call_lose;
+
+ /* Process program headers again after load segments are mapped in
+ case processing requires accessing those segments. */
+ for (ph = phdr; ph < &phdr[l->l_phnum]; ++ph)
+ switch (ph->p_type)
+ {
+ case PT_GNU_PROPERTY:
+ if (_dl_process_pt_gnu_property (l, ph))
+ {
+ errstring = N_("cannot process GNU property segment");
+ goto call_lose;
+ }
+ break;
+ }
}
if (l->l_ld == 0)
main_map->l_relro_size = ph->p_memsz;
break;
+ case PT_GNU_PROPERTY:
+ if (_dl_process_pt_gnu_property (main_map, ph))
+ _dl_error_printf (
+"ERROR: '%s': cannot process GNU property segment.\n", _dl_argv[0]);
+ break;
+
case PT_NOTE:
if (_rtld_process_pt_note (main_map, ph))
_dl_error_printf ("\
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
--- /dev/null
+/* 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
+ <https://www.gnu.org/licenses/>. */
+
+#include <unistd.h>
+#include <errno.h>
+#include <libintl.h>
+#include <ldsodefs.h>
+
+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))
+ {
+ ElfW(Addr) start = phdr->p_vaddr + map->l_addr;
+ ElfW(Addr) len = phdr->p_memsz;
+ if (__mprotect ((void *) 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);
+}
--- /dev/null
+/* 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
+ <https://www.gnu.org/licenses/>. */
+
+#ifndef _DL_PROP_H
+#define _DL_PROP_H
+
+#include <not-cancel.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__ ((unused))
+_dl_process_aarch64_property (struct link_map *l,
+ const ElfW(Nhdr) *note,
+ const ElfW(Addr) size,
+ const ElfW(Addr) align)
+{
+ /* The NT_GNU_PROPERTY_TYPE_0 note must be aligned to 4 bytes in
+ 32-bit objects and to 8 bytes in 64-bit objects. Skip notes
+ with incorrect alignment. */
+ if (align != (__ELF_NATIVE_CLASS / 8))
+ return;
+
+ const ElfW(Addr) start = (ElfW(Addr)) note;
+
+ unsigned int feature_1 = 0;
+ unsigned int last_type = 0;
+
+ while ((ElfW(Addr)) (note + 1) - start < size)
+ {
+ /* Find the NT_GNU_PROPERTY_TYPE_0 note. */
+ if (note->n_namesz == 4
+ && note->n_type == NT_GNU_PROPERTY_TYPE_0
+ && memcmp (note + 1, "GNU", 4) == 0)
+ {
+ /* Check for invalid property. */
+ if (note->n_descsz < 8
+ || (note->n_descsz % sizeof (ElfW(Addr))) != 0)
+ return;
+
+ /* Start and end of property array. */
+ unsigned char *ptr = (unsigned char *) (note + 1) + 4;
+ unsigned char *ptr_end = ptr + note->n_descsz;
+
+ do
+ {
+ unsigned int type = *(unsigned int *) ptr;
+ unsigned int datasz = *(unsigned int *) (ptr + 4);
+
+ /* Property type must be in ascending order. */
+ if (type < last_type)
+ return;
+
+ ptr += 8;
+ if ((ptr + datasz) > ptr_end)
+ return;
+
+ last_type = type;
+
+ if (type == GNU_PROPERTY_AARCH64_FEATURE_1_AND)
+ {
+ /* The size of GNU_PROPERTY_AARCH64_FEATURE_1_AND is 4
+ bytes. When seeing GNU_PROPERTY_AARCH64_FEATURE_1_AND,
+ we stop the search regardless if its size is correct
+ or not. There is no point to continue if this note
+ is ill-formed. */
+ if (datasz != 4)
+ return;
+
+ feature_1 = *(unsigned int *) ptr;
+ if ((feature_1 & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))
+ l->l_mach.bti = true;
+
+ /* Stop if we found the property note. */
+ return;
+ }
+ else if (type > GNU_PROPERTY_AARCH64_FEATURE_1_AND)
+ {
+ /* Stop since property type is in ascending order. */
+ return;
+ }
+
+ /* Check the next property item. */
+ ptr += ALIGN_UP (datasz, sizeof (ElfW(Addr)));
+ }
+ while ((ptr_end - ptr) >= 8);
+ }
+
+ note = ((const void *) note
+ + ELF_NOTE_NEXT_OFFSET (note->n_namesz, note->n_descsz,
+ align));
+ }
+}
+
+#ifdef FILEBUF_SIZE
+static inline int __attribute__ ((always_inline))
+_dl_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph,
+ int fd, struct filebuf *fbp)
+{
+ return 0;
+}
+#endif
+
+static inline int __attribute__ ((always_inline))
+_rtld_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph)
+{
+ return 0;
+}
+
+static inline int
+_dl_process_pt_gnu_property (struct link_map *l, const ElfW(Phdr) *ph)
+{
+ const ElfW(Nhdr) *note = (const void *) (ph->p_vaddr + l->l_addr);
+ _dl_process_aarch64_property (l, note, ph->p_memsz, ph->p_align);
+ return 0;
+}
+
+#endif /* _DL_PROP_H */
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
+#include <stdbool.h>
+
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. */
};
#define _DL_PROP_H
/* The following functions are used by the dynamic loader and the
- dlopen machinery to process PT_NOTE entries in the binary or
- shared object. The notes can be used to change the behaviour of
- the loader, and as such offer a flexible mechanism for hooking in
- various checks related to ABI tags or implementing "flag day" ABI
- transitions. */
+ dlopen machinery to process PT_NOTE and PT_GNU_PROPERTY entries in
+ the binary or shared object. The notes can be used to change the
+ behaviour of the loader, and as such offer a flexible mechanism
+ for hooking in various checks related to ABI tags or implementing
+ "flag day" ABI transitions. */
static inline void __attribute__ ((always_inline))
_rtld_main_check (struct link_map *m, const char *program)
return 0;
}
+static inline int __attribute__ ((always_inline))
+_dl_process_pt_gnu_property (struct link_map *l, const ElfW(Phdr) *ph)
+{
+ return 0;
+}
+
#endif /* _DL_PROP_H */
#define HWCAP2_BF16 (1 << 14)
#define HWCAP2_DGH (1 << 15)
#define HWCAP2_RNG (1 << 16)
+#define HWCAP2_BTI (1 << 17)
--- /dev/null
+/* Definitions for POSIX memory map interface. Linux/AArch64 version.
+ Copyright (C) 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
+ <https://www.gnu.org/licenses/>. */
+
+#ifndef _SYS_MMAN_H
+# error "Never use <bits/mman.h> directly; include <sys/mman.h> instead."
+#endif
+
+/* AArch64 specific definitions, should be in sync with
+ arch/arm64/include/uapi/asm/mman.h. */
+
+#define PROT_BTI 0x10
+
+#include <bits/mman-map-flags-generic.h>
+
+/* Include generic Linux declarations. */
+#include <bits/mman-linux.h>
if ((dczid & DCZID_DZP_MASK) == 0)
cpu_features->zva_size = 4 << (dczid & DCZID_BS_MASK);
+
+ /* Check if BTI is supported. */
+ cpu_features->bti = GLRO (dl_hwcap2) & HWCAP2_BTI;
}
#define _CPU_FEATURES_AARCH64_H
#include <stdint.h>
+#include <stdbool.h>
#define MIDR_PARTNUM_SHIFT 4
#define MIDR_PARTNUM_MASK (0xfff << MIDR_PARTNUM_SHIFT)
{
uint64_t midr_el1;
unsigned zva_size;
+ bool bti;
};
#endif /* _CPU_FEATURES_AARCH64_H */
return 0;
}
+static inline int __attribute__ ((always_inline))
+_dl_process_pt_gnu_property (struct link_map *l, const ElfW(Phdr) *ph)
+{
+ return 0;
+}
+
#endif /* _DL_PROP_H */
projects / thirdparty / glibc.git / commitdiff
