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.
Will