Re: seccomp: add "seccomp" syscall

On Mon, Aug 11, 2014 at 1:07 PM, Geert Uytterhoeven
[off-list ref] wrote:

Hi Kees,

v3.17 is gonna get a lot of new syscalls...

4 so far! :P

On Wed, Aug 6, 2014 at 6:27 PM, Linux Kernel Mailing List
[off-list ref] wrote:

quoted

Gitweb:     http://git.kernel.org/linus/;a=commit;h=48dc92b9fc3926844257316e75ba11eb5c742b2c
Commit:     48dc92b9fc3926844257316e75ba11eb5c742b2c
Parent:     3b23dd12846215eff4afb073366b80c0c4d7543e
Refname:    refs/heads/master
Author:     Kees Cook [off-list ref]
AuthorDate: Wed Jun 25 16:08:24 2014 -0700
Committer:  Kees Cook [off-list ref]
CommitDate: Fri Jul 18 12:13:37 2014 -0700

    seccomp: add "seccomp" syscall

    This adds the new "seccomp" syscall with both an "operation" and "flags"
    parameter for future expansion. The third argument is a pointer value,
    used with the SECCOMP_SET_MODE_FILTER operation. Currently, flags must
    be 0. This is functionally equivalent to prctl(PR_SET_SECCOMP, ...).

    In addition to the TSYNC flag later in this patch series, there is a
    non-zero chance that this syscall could be used for configuring a fixed
    argument area for seccomp-tracer-aware processes to pass syscall arguments
    in the future. Hence, the use of "seccomp" not simply "seccomp_add_filter"
    for this syscall. Additionally, this syscall uses operation, flags,
    and user pointer for arguments because strictly passing arguments via
    a user pointer would mean seccomp itself would be unable to trivially
    filter the seccomp syscall itself.

    Signed-off-by: Kees Cook [off-list ref]
    Reviewed-by: Oleg Nesterov [off-list ref]
    Reviewed-by: Andy Lutomirski [off-list ref]

Is this something that I should enable?

As it depends on CONFIG_SECCOMP, it only makes sense on architectures that
already support CONFIG_SECCOMP, right?
Does it make sense to reserve a syscall slot for it on architectures that
don't support it yet?

I don't see a good reason to reserve the syscall slot if seccomp
filter is not already implemented. I've CCed linux-api in case there
is something I'm not considering, though.

FWIW, if someone wants to add it for m68k, the steps to support
seccomp are listed in the arch/Kconfig for HAVE_ARCH_SECCOMP_FILTER.

-Kees

-- 
Kees Cook
Chrome OS Security