On Thu, Jan 21, 2021, Borislav Petkov wrote:
> On Mon, Dec 28, 2020 at 11:15:11AM -0800, Sean Christopherson wrote:
> > Alternatively, could the kernel case use insn_decode_regs()? If
> > vc_fetch_insn_kernel() were also modified to mirror insn_fetch_from_user(),
> > the
> > two code paths could be unified except for the the fetch and the PFEC. E.g.
>
> Personal Firearms Eligibility Check?
Ha, Page Fault Error Code.
> In any case, I prefer simple, easy to follow code at a quick glance.
> Stuff like...
>
> >
> > static int vc_fetch_insn_kernel(struct es_em_ctxt *ctxt,
> > unsigned char *buffer)
> > {
> > if (copy_from_kernel_nofault(buffer, (unsigned char *)ctxt->regs->ip,
> > MAX_INSN_SIZE))
> > return 0;
> >
> > return MAX_INSN_SIZE;
> > }
> >
> > static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
> > {
> > char buffer[MAX_INSN_SIZE];
> > int nbytes;
> >
> > if (user_mode(ctxt->regs))
> > nbytes = insn_fetch_from_user(ctxt->regs, buffer);
> > else
> > nbytes = vc_fetch_insn_kernel(ctxt, buffer);
> >
> > if (!nbytes) {
> > ctxt->fi.vector = X86_TRAP_PF;
> > ctxt->fi.error_code = X86_PF_INSTR;
> > if (user_mode(ctxt->regs))
>
> ... this second repeated check here is not what I would call that.
But then you're stuck maintaining two separate flows that do the same thing.
> But this is my personal preference only so it's up for a vote now.
Rock Paper Scissors?
