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Re: [PATCH] x86: Remove vsyscall usage
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: GNU C Library <libc-alpha at sourceware dot org>
- Date: Fri, 05 Jun 2015 15:59:38 -0300
- Subject: Re: [PATCH] x86: Remove vsyscall usage
- Authentication-results: sourceware.org; auth=none
- References: <553963C1 dot 2080600 at linaro dot org> <5550FF32 dot 5040708 at linaro dot org>
Ping.
On 11-05-2015 16:12, Adhemerval Zanella wrote:
> Ping.
>
> On 23-04-2015 18:27, Adhemerval Zanella wrote:
>> This patch removes the vsyscall usage for x86_64 port. As indicated
>> by kernel code comments [1], vsyscalls are a legacy ABI and its concept
>> is problematic:
>>
>> - It interferes with ASLR.
>> - It's awkward to write code that lives in kernel addresses but is
>> callable by userspace at fixed addresses.
>> - The whole concept is impossible for 32-bit compat userspace.
>> - UML cannot easily virtualize a vsyscall.
>>
>> The VDSO is a better approach for such functionality. Tested on i686,
>> x86_64, and x32.
>>
>> [1] arch/x86/kernel/vsyscall_64.c
>>
>> --
>>
>> * sysdeps/unix/sysv/linux/i386/gettimeofday.c
>> (__gettimeofday_syscall): Remove.
>> * sysdeps/unix/sysv/linux/i386/time.c (__time_syscall): Remove.
>> * sysdeps/unix/sysv/linux/x86/gettimeofday.c (__gettimeofday_syscall):
>> Add function.
>> (gettimeofday_ifunc): Use __gettimeofday_syscall as fallback mechanism
>> if vDSO is not present.
>> * sysdeps/unix/sysv/linux/x86/time.c (__time_syscall): Add function.
>> (time_ifunc): Use __time_syscall as fallback mechanism if vDSO is not
>> present.
>> * sysdeps/unix/sysv/linux/x86_64/gettimeofday.c: Remove file.
>> * sysdeps/unix/sysv/linux/x86_64/time.c: Likewise.
>>
>> ---
>>
>> diff --git a/sysdeps/unix/sysv/linux/i386/gettimeofday.c b/sysdeps/unix/sysv/linux/i386/gettimeofday.c
>> index 3e00eb4..fdb0fab 100644
>> --- a/sysdeps/unix/sysv/linux/i386/gettimeofday.c
>> +++ b/sysdeps/unix/sysv/linux/i386/gettimeofday.c
>> @@ -20,16 +20,6 @@
>>
>> #ifdef SHARED
>>
>> -# include <dl-vdso.h>
>> -# include <errno.h>
>> -
>> -/* If the vDSO is not available we fall back on the syscall. */
>> -static int
>> -__gettimeofday_syscall (struct timeval *tv, struct timezone *tz)
>> -{
>> - return INLINE_SYSCALL (gettimeofday, 2, tv, tz);
>> -}
>> -# define GETTIMEOFAY_FALLBACK (void*) (&__gettimeofday_syscall)
>> # undef libc_ifunc_hidden_def
>> # define libc_ifunc_hidden_def(name) \
>> libc_ifunc_hidden_def1 (__GI_##name, __gettimeofday_syscall)
>> diff --git a/sysdeps/unix/sysv/linux/i386/time.c b/sysdeps/unix/sysv/linux/i386/time.c
>> index e8a4e59..66b9a6c 100644
>> --- a/sysdeps/unix/sysv/linux/i386/time.c
>> +++ b/sysdeps/unix/sysv/linux/i386/time.c
>> @@ -18,17 +18,6 @@
>>
>> #ifdef SHARED
>>
>> -# include <dl-vdso.h>
>> -# include <errno.h>
>> -
>> -/* If the vDSO is not available we fall back on the old vsyscall. */
>> -static time_t
>> -__time_syscall (time_t *t)
>> -{
>> - INTERNAL_SYSCALL_DECL (err);
>> - return INTERNAL_SYSCALL (time, err, 1, t);
>> -}
>> -# define TIME_FALLBACK (void*) &__time_syscall
>> # undef libc_ifunc_hidden_def
>> # define libc_ifunc_hidden_def(name) \
>> libc_ifunc_hidden_def1 (__GI_##name, __time_syscall)
>> diff --git a/sysdeps/unix/sysv/linux/x86/gettimeofday.c b/sysdeps/unix/sysv/linux/x86/gettimeofday.c
>> index c820fd7..c9cb6ea 100644
>> --- a/sysdeps/unix/sysv/linux/x86/gettimeofday.c
>> +++ b/sysdeps/unix/sysv/linux/x86/gettimeofday.c
>> @@ -21,6 +21,14 @@
>> #ifdef SHARED
>>
>> # include <dl-vdso.h>
>> +# include <errno.h>
>> +
>> +/* If the vDSO is not available we fall back on the syscall. */
>> +static int
>> +__gettimeofday_syscall (struct timeval *tv, struct timezone *tz)
>> +{
>> + return INLINE_SYSCALL (gettimeofday, 2, tv, tz);
>> +}
>>
>> void *gettimeofday_ifunc (void) __asm__ ("__gettimeofday");
>>
>> @@ -31,7 +39,7 @@ gettimeofday_ifunc (void)
>>
>> /* If the vDSO is not available we fall back on the old vsyscall. */
>> return (_dl_vdso_vsym ("__vdso_gettimeofday", &linux26)
>> - ?: GETTIMEOFAY_FALLBACK);
>> + ?: (void*) (&__gettimeofday_syscall));
>> }
>> asm (".type __gettimeofday, %gnu_indirect_function");
>>
>> diff --git a/sysdeps/unix/sysv/linux/x86/time.c b/sysdeps/unix/sysv/linux/x86/time.c
>> index 1ab9248..3459e17 100644
>> --- a/sysdeps/unix/sysv/linux/x86/time.c
>> +++ b/sysdeps/unix/sysv/linux/x86/time.c
>> @@ -21,6 +21,15 @@
>> #ifdef SHARED
>>
>> #include <dl-vdso.h>
>> +#include <errno.h>
>> +
>> +/* If the vDSO is not available we fall back on the old vsyscall. */
>> +static time_t
>> +__time_syscall (time_t *t)
>> +{
>> + INTERNAL_SYSCALL_DECL (err);
>> + return INTERNAL_SYSCALL (time, err, 1, t);
>> +}
>>
>> void *time_ifunc (void) __asm__ ("time");
>>
>> @@ -29,7 +38,8 @@ time_ifunc (void)
>> {
>> PREPARE_VERSION_KNOWN (linux26, LINUX_2_6);
>>
>> - return _dl_vdso_vsym ("__vdso_time", &linux26) ?: TIME_FALLBACK;
>> + return _dl_vdso_vsym ("__vdso_time", &linux26)
>> + ?: (void*) &__time_syscall;
>> }
>> asm (".type time, %gnu_indirect_function");
>>
>> diff --git a/sysdeps/unix/sysv/linux/x86_64/gettimeofday.c b/sysdeps/unix/sysv/linux/x86_64/gettimeofday.c
>> deleted file mode 100644
>> index daa14de..0000000
>> --- a/sysdeps/unix/sysv/linux/x86_64/gettimeofday.c
>> +++ /dev/null
>> @@ -1,26 +0,0 @@
>> -/* Copyright (C) 2002-2015 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
>> - <http://www.gnu.org/licenses/>. */
>> -
>> -#include <sys/time.h>
>> -
>> -#ifdef SHARED
>> -/* If the vDSO is not available we fall back on the old vsyscall. */
>> -# define VSYSCALL_ADDR_vgettimeofday 0xffffffffff600000ul
>> -# define GETTIMEOFAY_FALLBACK (void*)VSYSCALL_ADDR_vgettimeofday
>> -#endif
>> -
>> -#include <sysdeps/unix/sysv/linux/x86/gettimeofday.c>
>> diff --git a/sysdeps/unix/sysv/linux/x86_64/time.c b/sysdeps/unix/sysv/linux/x86_64/time.c
>> deleted file mode 100644
>> index 6ceb819..0000000
>> --- a/sysdeps/unix/sysv/linux/x86_64/time.c
>> +++ /dev/null
>> @@ -1,24 +0,0 @@
>> -/* Copyright (C) 2001-2015 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
>> - <http://www.gnu.org/licenses/>. */
>> -
>> -#ifdef SHARED
>> -/* If the vDSO is not available we fall back on the old vsyscall. */
>> -#define VSYSCALL_ADDR_vtime 0xffffffffff600400
>> -#define TIME_FALLBACK (void*)VSYSCALL_ADDR_vtime
>> -#endif
>> -
>> -#include <sysdeps/unix/sysv/linux/x86/time.c>
>>