On Fri, Jul 18, 2014 at 3:16 PM, Kees Cook [off-list ref] wrote:

On Fri, Jul 18, 2014 at 2:18 PM, Andy Lutomirski [off-list ref] wrote:

quoted

populate_seccomp_data is expensive: it works by inspecting
task_pt_regs and various other bits to piece together all the
information, and it's does so in multiple partially redundant steps.

Arch-specific code in the syscall entry path can do much better.

Admittedly this adds a bit of additional room for error, but the
speedup should be worth it.

I still think we should gain either a note in the
HAVE_ARCH_SECCOMP_FILTER help text in arch/Kconfig, or possibly a new
section in Documentation/prctl/seccomp.txt (or similar) on how do
implement filter support for an architecture, that mentions the
arch-supplied seccomp_data and how two-phase can be done.

I would have sworn I did that.  I distinctly remember typing that
text.  I must have failed to commit it.

I'll send a followup patch.

--Andy

-Kees

--
Kees Cook
Chrome OS Security

-- 
Andy Lutomirski
AMA Capital Management, LLC