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 <[email protected]> > Signed-off-by: AKASHI Takahiro <[email protected]> > --- > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
