Re: Compat 32-bit syscall entry from 64-bit task!? [was: Re:[RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]

[Jamie Lokier]

Andi Kleen wrote:
> > Not everybody. There are programs which try hard to distinguish between
> > int80 and syscall. One such example is a sandbox for programming contests
> > I wrote several years ago. It analyses the instruction before EIP and as
> > it does not allow threads nor executing writeable memory, it should be
> > correct.
> 
> There are other ways to break it, like using the syscall itself to change
> input arguments or using ptrace from another process and other ways.
> 
> Generally there are so many races with ptrace that if you want to do
> things like that it's better to use a LSM. That's what they are for.

I could see the LSM approach working *if* there was an LSM module to
make it available to unpriviledged userspace.  I.e. a replacement for
ptrace() for this purpose.

It would be nice to be able to trace and check syscall strings properly.

-- Jamie
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