Re: [PATCH v3 09/16] elf: Move vDSO setup to rtld (BZ#24967)

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 02/01/2020 09:55, Siddhesh Poyarekar wrote:
> On 18/12/19 3:17 am, Adhemerval Zanella wrote:
>> Changes from previous version:
>>
>>   - Do not GLRO access on ifunc resolver, ut rather call the vDSO
>>     resolve function instead (dl_vdso_vsym).
>>
>> --
>>
>> This patch moves the vDSO setup from libc to loader code, just after
>> the vDSO link_map setup.  For static case the initialization
>> is moved to _dl_non_dynamic_init instead.
>>
>> Instead of using the mangled pointer, the vDSO data is set as
>> attribute_relro (on _rtld_global_ro for shared or _dl_vdso_* for
>> static).  It is read-only even with partial relro.
>>
>> It fixes BZ#24967 now that the vDSO pointer is setup earlier than
>> malloc interposition is called.
>>
>> Also, vDSO calls should not be a problem for static dlopen as
>> indicated by BZ#20802.  The vDSO pointer would be zero-initialized
>> and the syscall will be issued instead.
>>
>> Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
>> arm-linux-gnueabihf, powerpc64le-linux-gnu, powerpc64-linux-gnu,
>> powerpc-linux-gnu, s390x-linux-gnu, sparc64-linux-gnu, and
>> sparcv9-linux-gnu.  I also run some tests on mips.
>> ---
>>  csu/init-first.c                              |  4 -
>>  elf/dl-support.c                              |  7 ++
>>  elf/rtld.c                                    |  7 +-
>>  malloc/tst-interpose-aux.c                    |  5 ++
>>  sysdeps/generic/dl-vdso-setup.c               |  1 +
>>  sysdeps/generic/dl-vdso-setup.h               | 28 ++++++
>>  sysdeps/generic/dl-vdso.h                     | 30 +++++++
>>  sysdeps/generic/ldsodefs.h                    |  6 ++
>>  sysdeps/powerpc/powerpc32/backtrace.c         | 16 ++--
>>  sysdeps/powerpc/powerpc64/backtrace.c         |  8 +-
>>  sysdeps/unix/sysv/linux/aarch64/Makefile      |  1 -
>>  sysdeps/unix/sysv/linux/arm/Makefile          |  1 -
>>  sysdeps/unix/sysv/linux/dl-vdso-setup.c       | 81 +++++++++++++++++
>>  sysdeps/unix/sysv/linux/dl-vdso-setup.h       | 55 ++++++++++++
>>  sysdeps/unix/sysv/linux/dl-vdso.c             | 48 ----------
>>  sysdeps/unix/sysv/linux/dl-vdso.h             | 30 ++++---
>>  sysdeps/unix/sysv/linux/gettimeofday.c        |  3 +-
>>  sysdeps/unix/sysv/linux/init-first.c          | 90 -------------------
>>  sysdeps/unix/sysv/linux/libc-vdso.h           | 30 +------
>>  sysdeps/unix/sysv/linux/mips/Makefile         |  2 -
>>  sysdeps/unix/sysv/linux/powerpc/Makefile      |  1 -
>>  .../sysv/linux/powerpc/get_timebase_freq.c    |  5 +-
>>  sysdeps/unix/sysv/linux/powerpc/init-first.c  | 50 -----------
>>  sysdeps/unix/sysv/linux/powerpc/libc-vdso.h   | 10 ---
>>  sysdeps/unix/sysv/linux/riscv/Makefile        |  4 -
>>  sysdeps/unix/sysv/linux/riscv/flush-icache.c  |  2 +-
>>  sysdeps/unix/sysv/linux/s390/Makefile         |  4 -
>>  sysdeps/unix/sysv/linux/sparc/Makefile        |  4 -
>>  sysdeps/unix/sysv/linux/sysdep-vdso.h         |  6 +-
>>  sysdeps/unix/sysv/linux/time.c                |  3 +-
>>  sysdeps/unix/sysv/linux/x86/Makefile          |  4 -
>>  31 files changed, 257 insertions(+), 289 deletions(-)
>>  create mode 100644 sysdeps/generic/dl-vdso-setup.c
>>  create mode 100644 sysdeps/generic/dl-vdso-setup.h
>>  create mode 100644 sysdeps/generic/dl-vdso.h
>>  create mode 100644 sysdeps/unix/sysv/linux/dl-vdso-setup.c
>>  create mode 100644 sysdeps/unix/sysv/linux/dl-vdso-setup.h
>>  delete mode 100644 sysdeps/unix/sysv/linux/dl-vdso.c
>>  delete mode 100644 sysdeps/unix/sysv/linux/init-first.c
>>  delete mode 100644 sysdeps/unix/sysv/linux/powerpc/init-first.c
>>
> 
> OK with some minor nits fixed, see below.
> 
> Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

>> diff --git a/sysdeps/generic/dl-vdso-setup.h b/sysdeps/generic/dl-vdso-setup.h
>> new file mode 100644
>> index 0000000000..3d79bae317
>> --- /dev/null
>> +++ b/sysdeps/generic/dl-vdso-setup.h
>> @@ -0,0 +1,28 @@
>> +/* ELF symbol initialization functions for VDSO objects.
>> +   Copyright (C) 2019 Free Software Foundation, Inc.
> 
> Update copyright year.

Ack.

> 
>> +   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_VDSO_INIT_H
>> +#define _DL_VDSO_INIT_H
>> +
>> +/* Initialize the VDSO functions pointers.  */
>> +static inline void __attribute__ ((always_inline))
>> +setup_vdso_pointers (void)
>> +{
>> +}
>> +
>> +#endif
>> diff --git a/sysdeps/generic/dl-vdso.h b/sysdeps/generic/dl-vdso.h
>> new file mode 100644
>> index 0000000000..5651f49a1a
>> --- /dev/null
>> +++ b/sysdeps/generic/dl-vdso.h
>> @@ -0,0 +1,30 @@
>> +/* ELF symbol resolve functions for VDSO objects.
>> +   Copyright (C) 2019 Free Software Foundation, Inc.
> 
> Update copyright year.

Ack.

>> diff --git a/sysdeps/unix/sysv/linux/dl-vdso-setup.c b/sysdeps/unix/sysv/linux/dl-vdso-setup.c
>> new file mode 100644
>> index 0000000000..1069879f1a
>> --- /dev/null
>> +++ b/sysdeps/unix/sysv/linux/dl-vdso-setup.c
>> @@ -0,0 +1,81 @@
>> +/* Data for vDSO support.  Linux version.
>> +   Copyright (C) 2019 Free Software Foundation, Inc.
> 
> Update copyright year.

Ack.

> 
>> +   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/>.  */
>> +
>> +/* This file is included in three different modes for both static (libc.a)
>> +   and shared (rtld) modes:
>> +
>> +   1. PROCINFO_DECL is defined, meaning we are only interested in
>> +      declarations.  For static it requires use the extern keywork along with
>> +      the attribute_relro while for shared it will be embedded in the
>> +      rtld_global_ro.
>> +
>> +   2. PROCINFO_DECL and SHARED are not defined.  Nothing to do, the default
>> +      zero initializion is suffice.
>> +
>> +   3. PROCINFO_DECL is not defined while SHARED is.  Similar to 2., the zero
>> +      initialization of rtld_global_ro is suffice.  */
>> +
>> +#ifndef PROCINFO_CLASS
>> +# define PROCINFO_CLASS
>> +#endif
>> +
>> +#ifndef SHARED
>> +# define RELRO attribute_relro
>> +#else
>> +# define RELRO
>> +#endif
>> +
>> +#if defined PROCINFO_DECL || !defined SHARED
>> +# ifdef HAVE_CLOCK_GETTIME_VSYSCALL
>> +PROCINFO_CLASS int (*_dl_vdso_clock_gettime) (clockid_t,
>> +					      struct timespec *) RELRO;
>> +#endif
> 
> Fix indentation.

Ack.

> 
>> +# ifdef HAVE_GETTIMEOFDAY_VSYSCALL
>> +PROCINFO_CLASS int (*_dl_vdso_gettimeofday) (struct timeval *, void *) RELRO;
>> +#endif
> 
> Fix indentation.

Ack.