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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <7b32d3a81141aad6c52187d959ecf82d125a513c.1589552055.git.szabolcs.nagy@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Adhemerval Zanella via Libc-alpha Reply-To: Adhemerval Zanella Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" On 15/05/2020 11:40, Szabolcs Nagy wrote: > From: Sudakshina Das > > 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 LGTM with a just a nit below. Reviewed-by: Adhemerval Zanella > --- > elf/dl-load.c | 13 ++ > elf/rtld.c | 6 + > sysdeps/aarch64/Makefile | 4 + > sysdeps/aarch64/dl-bti.c | 54 +++++++ > sysdeps/aarch64/dl-prop.h | 145 ++++++++++++++++++ > sysdeps/aarch64/linkmap.h | 3 + > sysdeps/generic/dl-prop.h | 16 +- > sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h | 1 + > sysdeps/unix/sysv/linux/aarch64/bits/mman.h | 31 ++++ > .../unix/sysv/linux/aarch64/cpu-features.c | 3 + > .../unix/sysv/linux/aarch64/cpu-features.h | 2 + > sysdeps/x86/dl-prop.h | 6 + > 12 files changed, 279 insertions(+), 5 deletions(-) > create mode 100644 sysdeps/aarch64/dl-bti.c > create mode 100644 sysdeps/aarch64/dl-prop.h > create mode 100644 sysdeps/unix/sysv/linux/aarch64/bits/mman.h > > diff --git a/elf/dl-load.c b/elf/dl-load.c > index 06f2ba7264..9c37ec1098 100644 > --- a/elf/dl-load.c > +++ b/elf/dl-load.c > @@ -1188,6 +1188,19 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd, > maplength, has_holes, loader); > if (__glibc_unlikely (errstring != NULL)) > goto call_lose; > + > + /* Process program headers again after load segments are mapped. */ Maybe add a brief explanation of why it is done after load segment mapping? > + 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) Ok. > diff --git a/elf/rtld.c b/elf/rtld.c > index 5ccc3c2dbb..97a0bbf4dc 100644 > --- a/elf/rtld.c > +++ b/elf/rtld.c > @@ -1506,6 +1506,12 @@ of this helper program; chances are you did not intend to run this program.\n\ > 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 ("\ Ok. > 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 Ok. > diff --git a/sysdeps/aarch64/dl-bti.c b/sysdeps/aarch64/dl-bti.c > new file mode 100644 > index 0000000000..6003686601 > --- /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)) > + { > + 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 (EINVAL, map->l_name, "dlopen", > + N_("mprotect failed to turn on BTI")); Is EINVAL the only possible error here (EACCES or ENOMEM might be still possible)? > + } > + } > + 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); > +} Ok. > diff --git a/sysdeps/aarch64/dl-prop.h b/sysdeps/aarch64/dl-prop.h > new file mode 100644 > index 0000000000..b6f8a88667 > --- /dev/null > +++ b/sysdeps/aarch64/dl-prop.h > @@ -0,0 +1,145 @@ > +/* 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 > + > +#include > + > +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 */ Ok. > 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. */ > }; Ok. > diff --git a/sysdeps/generic/dl-prop.h b/sysdeps/generic/dl-prop.h > index 6b0f2aa95a..4192049739 100644 > --- a/sysdeps/generic/dl-prop.h > +++ b/sysdeps/generic/dl-prop.h > @@ -20,11 +20,11 @@ > #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) > @@ -51,4 +51,10 @@ _rtld_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph) > 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 */ Ok. > diff --git a/sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h b/sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h > index 4ee14b4208..af90d8a626 100644 > --- a/sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h > +++ b/sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h > @@ -72,3 +72,4 @@ > #define HWCAP2_BF16 (1 << 14) > #define HWCAP2_DGH (1 << 15) > #define HWCAP2_RNG (1 << 16) > +#define HWCAP2_BTI (1 << 17) Ok. > diff --git a/sysdeps/unix/sysv/linux/aarch64/bits/mman.h b/sysdeps/unix/sysv/linux/aarch64/bits/mman.h > new file mode 100644 > index 0000000000..ecae046344 > --- /dev/null > +++ b/sysdeps/unix/sysv/linux/aarch64/bits/mman.h > @@ -0,0 +1,31 @@ > +/* 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 > + . */ > + > +#ifndef _SYS_MMAN_H > +# error "Never use directly; include instead." > +#endif > + > +/* AArch64 specific definitions, should be in sync with > + arch/arm64/include/uapi/asm/mman.h. */ > + > +#define PROT_BTI 0x10 > + > +#include > + > +/* Include generic Linux declarations. */ > +#include Ok (although I am still not sure if this should be inside a __USE_MISC). > diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c > index 896c588fee..b9ab827aca 100644 > --- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c > +++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c > @@ -83,4 +83,7 @@ init_cpu_features (struct cpu_features *cpu_features) > > 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; > } Ok. > diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.h b/sysdeps/unix/sysv/linux/aarch64/cpu-features.h > index 1389cea1b3..a81f186ec2 100644 > --- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.h > +++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.h > @@ -20,6 +20,7 @@ > #define _CPU_FEATURES_AARCH64_H > > #include > +#include > > #define MIDR_PARTNUM_SHIFT 4 > #define MIDR_PARTNUM_MASK (0xfff << MIDR_PARTNUM_SHIFT) > @@ -64,6 +65,7 @@ struct cpu_features > { > uint64_t midr_el1; > unsigned zva_size; > + bool bti; > }; > > #endif /* _CPU_FEATURES_AARCH64_H */ Ok. > diff --git a/sysdeps/x86/dl-prop.h b/sysdeps/x86/dl-prop.h > index 516f88ea80..8649314f9d 100644 > --- a/sysdeps/x86/dl-prop.h > +++ b/sysdeps/x86/dl-prop.h > @@ -191,4 +191,10 @@ _rtld_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph) > 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 */ > Ok.