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glibc/sysdeps/unix/sysv/linux/x86_64/sysdep.h
Adhemerval Zanella 461cab1de7 linux: Add support for getrandom vDSO 
Linux 6.11 has getrandom() in vDSO. It operates on a thread-local opaque
state allocated with mmap using flags specified by the vDSO.

Multiple states are allocated at once, as many as fit into a page, and
these are held in an array of available states to be doled out to each
thread upon first use, and recycled when a thread terminates. As these
states run low, more are allocated.

To make this procedure async-signal-safe, a simple guard is used in the
LSB of the opaque state address, falling back to the syscall if there's
reentrancy contention.

Also, _Fork() is handled by blocking signals on opaque state allocation
(so _Fork() always sees a consistent state even if it interrupts a
getrandom() call) and by iterating over the thread stack cache on
reclaim_stack. Each opaque state will be in the free states list
(grnd_alloc.states) or allocated to a running thread.

The cancellation is handled by always using GRND_NONBLOCK flags while
calling the vDSO, and falling back to the cancellable syscall if the
kernel returns EAGAIN (would block). Since getrandom is not defined by
POSIX and cancellation is supported as an extension, the cancellation is
handled as 'may occur' instead of 'shall occur' [1], meaning that if
vDSO does not block (the expected behavior) getrandom will not act as a
cancellation entrypoint. It avoids a pthread_testcancel call on the fast
path (different than 'shall occur' functions, like sem_wait()).

It is currently enabled for x86_64, which is available in Linux 6.11,
and aarch64, powerpc32, powerpc64, loongarch64, and s390x, which are
available in Linux 6.12.

Link: https://pubs.opengroup.org/onlinepubs/9799919799/nframe.html [1]
Co-developed-by: Jason A. Donenfeld <Jason@zx2c4.com>
Tested-by: Jason A. Donenfeld <Jason@zx2c4.com> # x86_64
Tested-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> # x86_64, aarch64
Tested-by: Xi Ruoyao <xry111@xry111.site> # x86_64, aarch64, loongarch64
Tested-by: Stefan Liebler <stli@linux.ibm.com> # s390x
2024-11-12 14:42:12 -03:00

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/* Copyright (C) 2001-2024 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 _LINUX_X86_64_SYSDEP_H
#define _LINUX_X86_64_SYSDEP_H 1
/* There is some commonality. */
#include <sysdeps/unix/sysv/linux/sysdep.h>
#include <sysdeps/unix/x86_64/sysdep.h>
#include <tls.h>
/* Defines RTLD_PRIVATE_ERRNO. */
#include <dl-sysdep.h>
/* For Linux we can use the system call table in the header file
/usr/include/asm/unistd.h
of the kernel. But these symbols do not follow the SYS_* syntax
so we have to redefine the `SYS_ify' macro here. */
#undef SYS_ify
#define SYS_ify(syscall_name) __NR_##syscall_name
#ifdef __ASSEMBLER__
/* Linux uses a negative return value to indicate syscall errors,
unlike most Unices, which use the condition codes' carry flag.
Since version 2.1 the return value of a system call might be
negative even if the call succeeded. E.g., the `lseek' system call
might return a large offset. Therefore we must not anymore test
for < 0, but test for a real error by making sure the value in %eax
is a real error number. Linus said he will make sure the no syscall
returns a value in -1 .. -4095 as a valid result so we can safely
test with -4095. */
/* We don't want the label for the error handle to be global when we define
it here. */
# undef SYSCALL_ERROR_LABEL
# ifdef PIC
# undef SYSCALL_ERROR_LABEL
# define SYSCALL_ERROR_LABEL 0f
# else
# undef SYSCALL_ERROR_LABEL
# define SYSCALL_ERROR_LABEL syscall_error
# endif
/* PSEUDO and T_PSEUDO macros have 2 extra arguments for unsigned long
int arguments. */
# define PSEUDOS_HAVE_ULONG_INDICES 1
# ifndef SYSCALL_ULONG_ARG_1
# define SYSCALL_ULONG_ARG_1 0
# define SYSCALL_ULONG_ARG_2 0
# endif
# undef PSEUDO
# if SYSCALL_ULONG_ARG_1
# define PSEUDO(name, syscall_name, args, ulong_arg_1, ulong_arg_2) \
.text; \
ENTRY (name) \
DO_CALL (syscall_name, args, ulong_arg_1, ulong_arg_2); \
cmpq $-4095, %rax; \
jae SYSCALL_ERROR_LABEL
# else
# define PSEUDO(name, syscall_name, args) \
.text; \
ENTRY (name) \
DO_CALL (syscall_name, args, 0, 0); \
cmpq $-4095, %rax; \
jae SYSCALL_ERROR_LABEL
# endif
# undef PSEUDO_END
# define PSEUDO_END(name) \
SYSCALL_ERROR_HANDLER \
END (name)
# undef PSEUDO_NOERRNO
# if SYSCALL_ULONG_ARG_1
# define PSEUDO_NOERRNO(name, syscall_name, args, ulong_arg_1, ulong_arg_2) \
.text; \
ENTRY (name) \
DO_CALL (syscall_name, args, ulong_arg_1, ulong_arg_2)
# else
# define PSEUDO_NOERRNO(name, syscall_name, args) \
.text; \
ENTRY (name) \
DO_CALL (syscall_name, args, 0, 0)
# endif
# undef PSEUDO_END_NOERRNO
# define PSEUDO_END_NOERRNO(name) \
END (name)
# define ret_NOERRNO ret
# undef PSEUDO_ERRVAL
# if SYSCALL_ULONG_ARG_1
# define PSEUDO_ERRVAL(name, syscall_name, args, ulong_arg_1, ulong_arg_2) \
.text; \
ENTRY (name) \
DO_CALL (syscall_name, args, ulong_arg_1, ulong_arg_2); \
negq %rax
# else
# define PSEUDO_ERRVAL(name, syscall_name, args) \
.text; \
ENTRY (name) \
DO_CALL (syscall_name, args, 0, 0); \
negq %rax
# endif
# undef PSEUDO_END_ERRVAL
# define PSEUDO_END_ERRVAL(name) \
END (name)
# define ret_ERRVAL ret
# if defined PIC && RTLD_PRIVATE_ERRNO
# define SYSCALL_SET_ERRNO \
lea rtld_errno(%rip), %RCX_LP; \
neg %eax; \
movl %eax, (%rcx)
# else
# if IS_IN (libc)
# define SYSCALL_ERROR_ERRNO __libc_errno
# else
# define SYSCALL_ERROR_ERRNO errno
# endif
# define SYSCALL_SET_ERRNO \
movq SYSCALL_ERROR_ERRNO@GOTTPOFF(%rip), %rcx;\
neg %eax; \
movl %eax, %fs:(%rcx);
# endif
# ifndef PIC
# define SYSCALL_ERROR_HANDLER /* Nothing here; code in sysdep.S is used. */
# else
# define SYSCALL_ERROR_HANDLER \
0: \
SYSCALL_SET_ERRNO; \
or $-1, %RAX_LP; \
ret;
# endif /* PIC */
/* The Linux/x86-64 kernel expects the system call parameters in
registers according to the following table:
syscall number rax
arg 1 rdi
arg 2 rsi
arg 3 rdx
arg 4 r10
arg 5 r8
arg 6 r9
The Linux kernel uses and destroys internally these registers:
return address from
syscall rcx
eflags from syscall r11
Normal function call, including calls to the system call stub
functions in the libc, get the first six parameters passed in
registers and the seventh parameter and later on the stack. The
register use is as follows:
system call number in the DO_CALL macro
arg 1 rdi
arg 2 rsi
arg 3 rdx
arg 4 rcx
arg 5 r8
arg 6 r9
We have to take care that the stack is aligned to 16 bytes. When
called the stack is not aligned since the return address has just
been pushed.
Syscalls of more than 6 arguments are not supported. */
# undef DO_CALL
# define DO_CALL(syscall_name, args, ulong_arg_1, ulong_arg_2) \
DOARGS_##args \
ZERO_EXTEND_##ulong_arg_1 \
ZERO_EXTEND_##ulong_arg_2 \
movl $SYS_ify (syscall_name), %eax; \
syscall;
# define DOARGS_0 /* nothing */
# define DOARGS_1 /* nothing */
# define DOARGS_2 /* nothing */
# define DOARGS_3 /* nothing */
# define DOARGS_4 movq %rcx, %r10;
# define DOARGS_5 DOARGS_4
# define DOARGS_6 DOARGS_5
# define ZERO_EXTEND_0 /* nothing */
# define ZERO_EXTEND_1 /* nothing */
# define ZERO_EXTEND_2 /* nothing */
# define ZERO_EXTEND_3 /* nothing */
# define ZERO_EXTEND_4 /* nothing */
# define ZERO_EXTEND_5 /* nothing */
# define ZERO_EXTEND_6 /* nothing */
#else /* !__ASSEMBLER__ */
/* Registers clobbered by syscall. */
# define REGISTERS_CLOBBERED_BY_SYSCALL "cc", "r11", "cx"
/* NB: This also works when X is an array. For an array X, type of
(X) - (X) is ptrdiff_t, which is signed, since size of ptrdiff_t
== size of pointer, cast is a NOP. */
#define TYPEFY1(X) __typeof__ ((X) - (X))
/* Explicit cast the argument. */
#define ARGIFY(X) ((TYPEFY1 (X)) (X))
/* Create a variable 'name' based on type of variable 'X' to avoid
explicit types. */
#define TYPEFY(X, name) __typeof__ (ARGIFY (X)) name
#undef INTERNAL_SYSCALL
#define INTERNAL_SYSCALL(name, nr, args...) \
internal_syscall##nr (SYS_ify (name), args)
#undef INTERNAL_SYSCALL_NCS
#define INTERNAL_SYSCALL_NCS(number, nr, args...) \
internal_syscall##nr (number, args)
#undef internal_syscall0
#define internal_syscall0(number, dummy...) \
({ \
unsigned long int resultvar; \
asm volatile ( \
"syscall\n\t" \
: "=a" (resultvar) \
: "0" (number) \
: "memory", REGISTERS_CLOBBERED_BY_SYSCALL); \
(long int) resultvar; \
})
#undef internal_syscall1
#define internal_syscall1(number, arg1) \
({ \
unsigned long int resultvar; \
TYPEFY (arg1, __arg1) = ARGIFY (arg1); \
register TYPEFY (arg1, _a1) asm ("rdi") = __arg1; \
asm volatile ( \
"syscall\n\t" \
: "=a" (resultvar) \
: "0" (number), "r" (_a1) \
: "memory", REGISTERS_CLOBBERED_BY_SYSCALL); \
(long int) resultvar; \
})
#undef internal_syscall2
#define internal_syscall2(number, arg1, arg2) \
({ \
unsigned long int resultvar; \
TYPEFY (arg2, __arg2) = ARGIFY (arg2); \
TYPEFY (arg1, __arg1) = ARGIFY (arg1); \
register TYPEFY (arg2, _a2) asm ("rsi") = __arg2; \
register TYPEFY (arg1, _a1) asm ("rdi") = __arg1; \
asm volatile ( \
"syscall\n\t" \
: "=a" (resultvar) \
: "0" (number), "r" (_a1), "r" (_a2) \
: "memory", REGISTERS_CLOBBERED_BY_SYSCALL); \
(long int) resultvar; \
})
#undef internal_syscall3
#define internal_syscall3(number, arg1, arg2, arg3) \
({ \
unsigned long int resultvar; \
TYPEFY (arg3, __arg3) = ARGIFY (arg3); \
TYPEFY (arg2, __arg2) = ARGIFY (arg2); \
TYPEFY (arg1, __arg1) = ARGIFY (arg1); \
register TYPEFY (arg3, _a3) asm ("rdx") = __arg3; \
register TYPEFY (arg2, _a2) asm ("rsi") = __arg2; \
register TYPEFY (arg1, _a1) asm ("rdi") = __arg1; \
asm volatile ( \
"syscall\n\t" \
: "=a" (resultvar) \
: "0" (number), "r" (_a1), "r" (_a2), "r" (_a3) \
: "memory", REGISTERS_CLOBBERED_BY_SYSCALL); \
(long int) resultvar; \
})
#undef internal_syscall4
#define internal_syscall4(number, arg1, arg2, arg3, arg4) \
({ \
unsigned long int resultvar; \
TYPEFY (arg4, __arg4) = ARGIFY (arg4); \
TYPEFY (arg3, __arg3) = ARGIFY (arg3); \
TYPEFY (arg2, __arg2) = ARGIFY (arg2); \
TYPEFY (arg1, __arg1) = ARGIFY (arg1); \
register TYPEFY (arg4, _a4) asm ("r10") = __arg4; \
register TYPEFY (arg3, _a3) asm ("rdx") = __arg3; \
register TYPEFY (arg2, _a2) asm ("rsi") = __arg2; \
register TYPEFY (arg1, _a1) asm ("rdi") = __arg1; \
asm volatile ( \
"syscall\n\t" \
: "=a" (resultvar) \
: "0" (number), "r" (_a1), "r" (_a2), "r" (_a3), "r" (_a4) \
: "memory", REGISTERS_CLOBBERED_BY_SYSCALL); \
(long int) resultvar; \
})
#undef internal_syscall5
#define internal_syscall5(number, arg1, arg2, arg3, arg4, arg5) \
({ \
unsigned long int resultvar; \
TYPEFY (arg5, __arg5) = ARGIFY (arg5); \
TYPEFY (arg4, __arg4) = ARGIFY (arg4); \
TYPEFY (arg3, __arg3) = ARGIFY (arg3); \
TYPEFY (arg2, __arg2) = ARGIFY (arg2); \
TYPEFY (arg1, __arg1) = ARGIFY (arg1); \
register TYPEFY (arg5, _a5) asm ("r8") = __arg5; \
register TYPEFY (arg4, _a4) asm ("r10") = __arg4; \
register TYPEFY (arg3, _a3) asm ("rdx") = __arg3; \
register TYPEFY (arg2, _a2) asm ("rsi") = __arg2; \
register TYPEFY (arg1, _a1) asm ("rdi") = __arg1; \
asm volatile ( \
"syscall\n\t" \
: "=a" (resultvar) \
: "0" (number), "r" (_a1), "r" (_a2), "r" (_a3), "r" (_a4), \
"r" (_a5) \
: "memory", REGISTERS_CLOBBERED_BY_SYSCALL); \
(long int) resultvar; \
})
#undef internal_syscall6
#define internal_syscall6(number, arg1, arg2, arg3, arg4, arg5, arg6) \
({ \
unsigned long int resultvar; \
TYPEFY (arg6, __arg6) = ARGIFY (arg6); \
TYPEFY (arg5, __arg5) = ARGIFY (arg5); \
TYPEFY (arg4, __arg4) = ARGIFY (arg4); \
TYPEFY (arg3, __arg3) = ARGIFY (arg3); \
TYPEFY (arg2, __arg2) = ARGIFY (arg2); \
TYPEFY (arg1, __arg1) = ARGIFY (arg1); \
register TYPEFY (arg6, _a6) asm ("r9") = __arg6; \
register TYPEFY (arg5, _a5) asm ("r8") = __arg5; \
register TYPEFY (arg4, _a4) asm ("r10") = __arg4; \
register TYPEFY (arg3, _a3) asm ("rdx") = __arg3; \
register TYPEFY (arg2, _a2) asm ("rsi") = __arg2; \
register TYPEFY (arg1, _a1) asm ("rdi") = __arg1; \
asm volatile ( \
"syscall\n\t" \
: "=a" (resultvar) \
: "0" (number), "r" (_a1), "r" (_a2), "r" (_a3), "r" (_a4), \
"r" (_a5), "r" (_a6) \
: "memory", REGISTERS_CLOBBERED_BY_SYSCALL); \
(long int) resultvar; \
})
# define VDSO_NAME "LINUX_2.6"
# define VDSO_HASH 61765110
/* List of system calls which are supported as vsyscalls. */
# define HAVE_CLOCK_GETTIME64_VSYSCALL "__vdso_clock_gettime"
# define HAVE_GETTIMEOFDAY_VSYSCALL "__vdso_gettimeofday"
# define HAVE_TIME_VSYSCALL "__vdso_time"
# define HAVE_GETCPU_VSYSCALL "__vdso_getcpu"
# define HAVE_CLOCK_GETRES64_VSYSCALL "__vdso_clock_getres"
# define HAVE_GETRANDOM_VSYSCALL "__vdso_getrandom"
# define HAVE_CLONE3_WRAPPER 1
#endif /* __ASSEMBLER__ */
/* How to pass the off{64}_t argument on p{readv,writev}{64}. */
#undef LO_HI_LONG
#define LO_HI_LONG(val) (val), 0
/* Each shadow stack slot takes 8 bytes. Assuming that each stack
frame takes 256 bytes, this is used to compute shadow stack size
from stack size. */
#define STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT 5
#endif /* linux/x86_64/sysdep.h */
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