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Re: seccomp via utrace



On Tue, Mar 24, 2009 at 11:48:49AM +0100, Ingo Molnar wrote:
> 
> * Roland McGrath <roland redhat com> wrote:
> 
> > Here is a trivial module to implement the seccomp guts via utrace.  
> > I haven't tested it at all.  (AFAIK it was only ever used by 
> > cpushare, and that project might be defunct now.)
> > 
> > I'm not sure what Ingo had in mind for integrating this.  If it's 
> > just to reimplement the existing prctl interface, then this is 
> > about all you need--just s/_xxx// and fiddle the config et al to 
> > build this and not the old stuff.
> >
> > If the approach would be incremental, to leave the old stuff in 
> > place, then it might make more sense just to do a fresh new thing 
> > not providing that prctl interface at all.  A new thing could be a 
> > module, and define some /sys files or whatnot for its "constrain 
> > me now" hook. I think a sensible thing would not require 
> > asm/seccomp.h at all, and instead just let the userland setup feed 
> > in a set of syscall numbers. It could be that flexible while still 
> > being quite simple so that one could audit that setup code and be 
> > confident it has no holes.  Then future versions of cpushare (or 
> > whatever) would not need any special kernel support for new arch's 
> > nor to change the syscall set it wants to allow.
> 
> nice! The simplification factor is already significant:
> 
>   18 files changed, 116 insertions(+), 175 deletions(-)
> 
> That is what we want - to remove special TIF flag uses and replace 
> them with utrace driven machinery.
> 
> Another future target could be to replace TIF_SYSCALL_FTRACE [in the 
> latest tracing tree] with a similar utrace driven solution.
> 
> Regarding ptrace-via-utrace. What is the plan there? Am i looking 
> the right branch:
> 
> | earth4:~/linux.trees.git> git diff --stat 
> | linus/master..utrace/utrace-ptrace kernel/ptrace.c arch/x86/kernel/ptrace.c
> |  kernel/ptrace.c |  803 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> |  1 files changed, 794 insertions(+), 9 deletions(-)
> 
>  dc43527: Merge branch 'utrace' into utrace-ptrace
> 
> I'd have (perhaps foolishly) expected ptrace.c to get reduced in 
> size and arch/x86/kernel/ptrace.c eliminated - but that does not 
> seem to be direction of movement. What am i missing?

Thats because the version of ptrace.c you are looking at has both the
legacy implementation and the ptrace over utrace implementation with
#ifdefs to separate them out. I guess Roland wanted to keep the legacy
stuff around till the ptrace/utrace becomes stable enough.

Ananth


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