Re: [PATCH v7 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL

[AKASHI Takahiro]

On 10/09/2014 12:30 AM, Kees Cook wrote:
> On Wed, Oct 8, 2014 at 9:13 AM, Will Deacon <will.deacon@xxxxxxx> wrote:
> > 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@xxxxxxxxxxxx>
> > > Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
> > > ---
> > >   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?
>
> Personally, I'd rather see this land as-is in the arm64 tree, and then
> later optimize PTRACE_SET_SYSCALL out of arm/ and arm64/, especially
> since only these architectures implement this at the moment.

+1 :)

-Takahiro AKASHI

> This is my plan for the asm-generic seccomp.h too -- I'd rather avoid
> touching other architectures in this series, as it's easier to review
> this way. Then we can optimize the code in a separate series, which
> will have those changes isolated, etc.
>
> -Kees
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/