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    SubjectRe: [PATCH v6 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL
    Kees,

    On 08/27/2014 02:46 AM, Will Deacon wrote:
    > On Fri, Aug 22, 2014 at 01:19:13AM +0100, AKASHI Takahiro wrote:
    >> On 08/22/2014 01:47 AM, Kees Cook wrote:
    >>> On Thu, Aug 21, 2014 at 3:56 AM, AKASHI Takahiro
    >>> <takahiro.akashi@linaro.org> wrote:
    >>>> To allow tracer to be able to change/skip a system call by re-writing
    >>>> a syscall number, there are several approaches:
    >>>>
    >>>> (1) modify x8 register with ptrace(PTRACE_SETREGSET), and handle this case
    >>>> later on in syscall_trace_enter(), or
    >>>> (2) support ptrace(PTRACE_SET_SYSCALL) as on arm
    >>>>
    >>>> Thinking of the fact that user_pt_regs doesn't expose 'syscallno' to
    >>>> tracer as well as that secure_computing() expects a changed syscall number
    >>>> to be visible, especially case of -1, before this function returns in
    >>>> syscall_trace_enter(), we'd better take (2).
    >>>>
    >>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
    >>>
    >>> Thanks, I like having this on both arm and arm64.
    >>
    >> Yeah, having this simplified the code of syscall_trace_enter() a bit, but
    >> also imposes some restriction on arm64, too.
    >>
    >> > I wonder if other archs should add this option too.
    >>
    >> Do you think so? I assumed that SET_SYSCALL is to be avoided if possible.
    >>
    >> I also think that SET_SYSCALL should take an extra argument for a return value
    >> just in case of -1 (or we have SKIP_SYSCALL?).
    >
    > I think we should propose this as a new request in the generic ptrace code.
    > We can have an architecture-hook for actually setting the syscall, and allow
    > architectures to define their own implementation of the request so they can
    > be moved over one by one.

    What do you think about this request?

    -Takahiro AKASHI

    > Will
    >


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