Re: [kernel-hardening] 32/64 bitness restriction for pid namespace

[Solar Designer <solar@openwall.com>]

Vasiliy,

On Sat, Aug 13, 2011 at 07:12:20PM +0400, Vasiliy Kulikov wrote:
> Re: slowdown - my assumptions are:
> 
> 1) we don't want any slowdown for legitimate tasks - 64 bit tasks for 64
> bit containers and 32 bit tasks for 32 bit containers.
> 
> 2) slowdown of malicious (or broken) tasks is not important.

Right.

> /* work to do in syscall_trace_enter() */
> #define _TIF_WORK_SYSCALL_ENTRY	\
> 	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | _TIF_SYSCALL_AUDIT |	\
> 	 _TIF_SECCOMP | _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
> 
> 
> So, there is a mask, which is used to identify whether a syscall needs
> additional pre/post processing.  If divide syscall_trace_enter() into 3
> functions, we'll get what we want.  This will result in zero impact on
> the legitimate code (relavite to current behaviour).
> 
> One drawback - *tracesys clobbers EAX/RAX, so I still have to patch asm.

I haven't looked into the detail of this, but in general I like the
approach of reusing a check that is already in the code.  Please proceed
with this.

Thanks,

Alexander