> On Aug 23, 2019, at 1:55 PM, Sean Christopherson > <sean.j.christopher...@intel.com> wrote: > > Don't advance RIP or inject a single-step #DB if emulation signals a > fault. This logic applies to all state updates that are conditional on > clean retirement of the emulation instruction, e.g. updating RFLAGS was > previously handled by commit 38827dbd3fb85 ("KVM: x86: Do not update > EFLAGS on faulting emulation"). > > Not advancing RIP is likely a nop, i.e. ctxt->eip isn't updated with > ctxt->_eip until emulation "retires" anyways. Skipping #DB injection > fixes a bug reported by Andy Lutomirski where a #UD on SYSCALL due to > invalid state with RFLAGS.RF=1 would loop indefinitely due to emulation > overwriting the #UD with #DB and thus restarting the bad SYSCALL over > and over. > > Cc: Nadav Amit <nadav.a...@gmail.com> > Cc: sta...@vger.kernel.org > Reported-by: Andy Lutomirski <l...@kernel.org> > Fixes: 663f4c61b803 ("KVM: x86: handle singlestep during emulation") > Signed-off-by: Sean Christopherson <sean.j.christopher...@intel.com>
Seems fine. I guess I should’ve found it before… Consider running the relevant self-tests (e.g., single_test_syscall) to avoid regressions.