[PATCH 0/6] ptrace: introduce PTRACE_SET_SYSCALL_INFO API

[H. Peter Anvin]

This would seem like a very good idea. However, it is perhaps important 
to realize that it doesn't fully eliminate the problems with 64-bit 
arguments on 32-bit ABIs being handled differently (never mind 
inconsistencies in system call ABIs etc.) There isn't all that much that 
can be done about that directly, though.

	-hpa


On 1/7/25 15:01, Dmitry V. Levin wrote:
> 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.
> 
> Current implementation supports changing only those bits of system call
> information that are used by strace, 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 re-using struct ptrace_syscall_info.reserved to specify
> the additional details that should be set.  Currently, the reserved
> field of struct ptrace_syscall_info must be initialized with zeroes;
> arch, instruction_pointer, and stack_pointer fields are 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 [1].
> 
> 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)).
> 
> [1] https://lore.kernel.org/all/59505464-c84a-403d-972f-d4b2055eeaac@gmail.com/
> 
> Dmitry V. Levin (6):
>    Revert "arch: remove unused function syscall_set_arguments()"
>    syscall.h: add syscall_set_arguments() on remaining
>      HAVE_ARCH_TRACEHOOK arches
>    syscall.h: introduce syscall_set_nr()
>    ptrace_get_syscall_info: factor out ptrace_get_syscall_info_op
>    ptrace: introduce PTRACE_SET_SYSCALL_INFO request
>    selftests/ptrace: add a test case for PTRACE_SET_SYSCALL_INFO
> 
>   arch/arc/include/asm/syscall.h                |  20 +
>   arch/arm/include/asm/syscall.h                |  25 +
>   arch/arm64/include/asm/syscall.h              |  20 +
>   arch/csky/include/asm/syscall.h               |  13 +
>   arch/hexagon/include/asm/syscall.h            |  14 +
>   arch/loongarch/include/asm/syscall.h          |  15 +
>   arch/m68k/include/asm/syscall.h               |   7 +
>   arch/microblaze/include/asm/syscall.h         |   7 +
>   arch/mips/include/asm/syscall.h               |  53 +++
>   arch/nios2/include/asm/syscall.h              |  16 +
>   arch/openrisc/include/asm/syscall.h           |  13 +
>   arch/parisc/include/asm/syscall.h             |  19 +
>   arch/powerpc/include/asm/syscall.h            |  15 +
>   arch/riscv/include/asm/syscall.h              |  16 +
>   arch/s390/include/asm/syscall.h               |  19 +
>   arch/sh/include/asm/syscall_32.h              |  19 +
>   arch/sparc/include/asm/syscall.h              |  17 +
>   arch/um/include/asm/syscall-generic.h         |  19 +
>   arch/x86/include/asm/syscall.h                |  43 ++
>   arch/xtensa/include/asm/syscall.h             |  18 +
>   include/asm-generic/syscall.h                 |  30 ++
>   include/linux/ptrace.h                        |   3 +
>   include/uapi/linux/ptrace.h                   |   3 +-
>   kernel/ptrace.c                               | 154 ++++++-
>   tools/testing/selftests/ptrace/Makefile       |   2 +-
>   .../selftests/ptrace/set_syscall_info.c       | 436 ++++++++++++++++++
>   26 files changed, 994 insertions(+), 22 deletions(-)
>   create mode 100644 tools/testing/selftests/ptrace/set_syscall_info.c
>