Hi Akashi,
On Thu, Oct 02, 2014 at 10:46:11AM +0100, AKASHI Takahiro 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).
Reviewed-by: Kees Cook keescook@chromium.org Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.org
arch/arm64/include/uapi/asm/ptrace.h | 1 + arch/arm64/kernel/ptrace.c | 14 +++++++++++++- 2 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h index 6913643..49c6174 100644 --- a/arch/arm64/include/uapi/asm/ptrace.h +++ b/arch/arm64/include/uapi/asm/ptrace.h @@ -23,6 +23,7 @@ #include <asm/hwcap.h> +#define PTRACE_SET_SYSCALL 23 /*
- PSR bits
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index fe63ac5..2842f9f 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1082,7 +1082,19 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task) long arch_ptrace(struct task_struct *child, long request, unsigned long addr, unsigned long data) {
- return ptrace_request(child, request, addr, data);
- int ret;
- switch (request) {
case PTRACE_SET_SYSCALL:task_pt_regs(child)->syscallno = data;ret = 0;break;default:ret = ptrace_request(child, request, addr, data);break;- }
- return ret;
}
I still don't understand why this needs to be in arch-specific code. Can't we implement this in generic code and get architectures to implement something like syscall_set_nr if they want the generic interface?
Will