On 10/02/2021 09:57, Jan Beulich wrote: > When invoked by compat mode, mode_64bit() will be false at the start of > emulation. The logic after complete_insn, however, needs to consider the > mode switched into, in particular to avoid truncating RIP. > > Inspired by / paralleling and extending Linux commit 943dea8af21b ("KVM: > x86: Update emulator context mode if SYSENTER xfers to 64-bit mode"). > > While there, tighten a related assertion in x86_emulate_wrapper() - we > want to be sure to not switch into an impossible mode when the code gets > built for 32-bit only (as is possible for the test harness). > > Signed-off-by: Jan Beulich <jbeul...@suse.com> > --- > In principle we could drop SYSENTER's ctxt->lma dependency when setting > _regs.r(ip). I wasn't certain whether leaving it as is serves as kind of > documentation ... > > --- a/xen/arch/x86/x86_emulate/x86_emulate.c > +++ b/xen/arch/x86/x86_emulate/x86_emulate.c > @@ -6127,6 +6127,10 @@ x86_emulate( > (rc = ops->write_segment(x86_seg_ss, &sreg, ctxt)) ) > goto done; > > + if ( ctxt->lma ) > + /* In particular mode_64bit() needs to return true from here on. > */ > + ctxt->addr_size = ctxt->sp_size = 64;
I think this is fine as presented, but don't we want the logical opposite for SYSRET/SYSEXIT ? We truncate rip suitably already, but don't know what other checks may appear in the future. ~Andrew