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75 lines
2.8 KiB
75 lines
2.8 KiB
/*
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* Copyright (c) 2019 Andrew G. Morgan <morgan@kernel.org>
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*
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* This header, and the -lpsx library, provide a number of things to
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* support POSIX semantics for syscalls associated with the pthread
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* library. Linking this code is tricky and is done as follows:
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*
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* ld ... -lpsx -lpthread --wrap=pthread_create
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* or, gcc ... -lpsx -lpthread -Wl,-wrap,pthread_create
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*
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* glibc provides a subset of this functionality natively through the
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* nptl:setxid mechanism and could implement psx_syscall() directly
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* using that style of functionality but, as of 2019-11-30, the setxid
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* mechanism is limited to 9 specific set*() syscalls that do not
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* support the syscall6 API (needed for prctl functions and the ambient
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* capabilities set for example).
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*/
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#ifndef _SYS_PSX_SYSCALL_H
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#define _SYS_PSX_SYSCALL_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include <pthread.h>
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/*
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* psx_syscall performs the specified syscall on all psx registered
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* threads. The mechanism by which this occurs is much less efficient
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* than a standard system call on Linux, so it should only be used
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* when POSIX semantics are required to change process relevant
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* security state.
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*
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* Glibc has native support for POSIX semantics on setgroups() and the
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* 8 set*[gu]id() functions. So, there is no need to use psx_syscall()
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* for these calls. This call exists for all the other system calls
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* that need to maintain parity on all pthreads of a program.
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*
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* Some macrology is used to allow the caller to provide only as many
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* arguments as needed, thus psx_syscall() cannot be used as a
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* function pointer. For those situations, we define psx_syscall3()
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* and psx_syscall6().
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*/
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#define psx_syscall(syscall_nr, ...) \
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__psx_syscall(syscall_nr, __VA_ARGS__, (long int) 6, (long int) 5, \
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(long int) 4, (long int) 3, (long int) 2, \
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(long int) 1, (long int) 0)
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long int __psx_syscall(long int syscall_nr, ...);
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long int psx_syscall3(long int syscall_nr,
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long int arg1, long int arg2, long int arg3);
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long int psx_syscall6(long int syscall_nr,
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long int arg1, long int arg2, long int arg3,
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long int arg4, long int arg5, long int arg6);
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/*
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* This function should be used by systems to obtain pointers to the
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* two syscall functions provided by the PSX library. A linkage trick
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* is to define this function as weak in a library that can optionally
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* use libpsx and then, should the caller link -lpsx, that library can
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* implicitly use these POSIX semantics syscalls. See libcap for an
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* example of this useage.
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*/
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void psx_load_syscalls(long int (**syscall_fn)(long int,
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long int, long int, long int),
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long int (**syscall6_fn)(long int,
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long int, long int, long int,
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long int, long int, long int));
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#ifdef __cplusplus
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}
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#endif
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#endif /* _SYS_PSX_SYSCALL_H */
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