Re: [patch] seccomp.2: Note that memory area is read-only

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Sat, Apr 18, 2015 at 04:37:35PM -0700, Kees Cook wrote:
> On Mon, Apr 6, 2015 at 8:29 AM, Michael Kerrisk (man-pages)
> <mtk.manpages@gmail.com> wrote:
> > Hi Kees,
> >
> > I recently was asked about the point below, and had to go check the code
> > to be sure, since the man page said nothing. It would be good to have
> > a confirmation: the seccomp_data buffer supplied to a seccomp BPF program
> > is read-only, right? (That is, one can't write to the buffer in order to
> > change the arguments that a system call actually receives.)
> 
> That's correct. If BPF even allows changing the data, it's not copied
> back to the syscall when it runs. Anything wanting to do things like
> that would need to use ptrace to catch the call an directly modify the
> registers before continuing with the call.

Today BPF programs can only read from seccomp_data buffer.
I think it would be an interesting feature to allow overwrite of
syscall arguments by the program on the fly... sometime in the future.