On Tue, May 19, 2020 at 01:03:25AM +0200, Thomas Gleixner wrote: > Jarkko Sakkinen <jarkko.sakki...@linux.intel.com> writes: > > On Mon, 2020-05-18 at 08:34 -0700, Andi Kleen wrote: > >> > Yes, for SGX this is functional feature because enclave entry points, > >> > thread control structures (aka TCS's), reset FSBASE and GSBASE registers > >> > to fixed (albeit user defined) values. And syscall's can be done only > >> > outside of enclave. > >> > > >> > This is a required feature for fancier runtimes (such as Graphene). > >> > >> Can you please explain a bit more? What do they need GS for? > > > > Apparently, uses only wrfsbase: > > > > https://raw.githubusercontent.com/oscarlab/graphene/master/Pal/src/host/Linux-SGX/db_misc.c > > > > I'm not too familiar with the codebase yet but by reading some research > > papers in the past the idea is to multiplex one TCS for multiple virtual > > threads inside the enclave. > > > > E.g. TCS could represent a vcpu for a libos type of container and on > > entry would pick on a thread and set fsbase accordingly for a thread > > control block. > > That justifies to write books which recommend to load a kernel module > which creates a full unpriviledged root hole. I bet none of these papers > ever mentioned that.
Fully agree that oot lkm for this is a worst idea ever. That's why I want to help with this. /Jarkko
