ptrace: introduce PTRACE_SET_SYSCALL_INFO request

PTRACE_SET_SYSCALL_INFO is a generic ptrace API that complements
PTRACE_GET_SYSCALL_INFO by letting the ptracer modify details of system
calls the tracee is blocked in.

This API allows ptracers to obtain and modify system call details in a
straightforward and architecture-agnostic way, providing a consistent way
of manipulating the system call number and arguments across architectures.

As in case of PTRACE_GET_SYSCALL_INFO, PTRACE_SET_SYSCALL_INFO also does
not aim to address numerous architecture-specific system call ABI
peculiarities, like differences in the number of system call arguments for
such system calls as pread64 and preadv.

The current implementation supports changing only those bits of system
call information that are used by strace system call tampering, namely,
syscall number, syscall arguments, and syscall return value.

Support of changing additional details returned by
PTRACE_GET_SYSCALL_INFO, such as instruction pointer and stack pointer,
could be added later if needed, by using struct ptrace_syscall_info.flags
to specify the additional details that should be set.  Currently, "flags"
and "reserved" fields of struct ptrace_syscall_info must be initialized
with zeroes; "arch", "instruction_pointer", and "stack_pointer" fields are
currently ignored.

PTRACE_SET_SYSCALL_INFO currently supports only PTRACE_SYSCALL_INFO_ENTRY,
PTRACE_SYSCALL_INFO_EXIT, and PTRACE_SYSCALL_INFO_SECCOMP operations. 
Other operations could be added later if needed.

Ideally, PTRACE_SET_SYSCALL_INFO should have been introduced along with
PTRACE_GET_SYSCALL_INFO, but it didn't happen.  The last straw that
convinced me to implement PTRACE_SET_SYSCALL_INFO was apparent failure to
provide an API of changing the first system call argument on riscv
architecture.

ptrace(2) man page:

long ptrace(enum __ptrace_request request, pid_t pid, void *addr, void *data);
...
PTRACE_SET_SYSCALL_INFO
       Modify information about the system call that caused the stop.
       The "data" argument is a pointer to struct ptrace_syscall_info
       that specifies the system call information to be set.
       The "addr" argument should be set to sizeof(struct ptrace_syscall_info)).

Link: https://lore.kernel.org/all/[email protected]/
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Dmitry V. Levin <[email protected]>
Reviewed-by: Alexey Gladkov <[email protected]>
Reviewed-by: Charlie Jenkins <[email protected]>
Tested-by: Charlie Jenkins <[email protected]>
Reviewed-by: Eugene Syromiatnikov <[email protected]>
Reviewed-by: Oleg Nesterov <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: Andreas Larsson <[email protected]>
Cc: anton ivanov <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Borislav Betkov <[email protected]>
Cc: Brian Cain <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Christian Zankel <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Davide Berardi <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Eugene Syromyatnikov <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Guo Ren <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Huacai Chen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Johannes Berg <[email protected]>
Cc: John Paul Adrian Glaubitz <[email protected]>
Cc: Jonas Bonn <[email protected]>
Cc: Maciej W. Rozycki <[email protected]>
Cc: Madhavan Srinivasan <[email protected]>
Cc: Max Filippov <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Michal Simek <[email protected]>
Cc: Mike Frysinger <[email protected]>
Cc: Naveen N Rao <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Renzo Davoi <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: Russel King <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Stafford Horne <[email protected]>
Cc: Stefan Kristiansson <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: Thomas Gleinxer <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Cc: Vineet Gupta <[email protected]>
Cc: WANG Xuerui <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yoshinori Sato <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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