On Sun, Mar 6, 2016 at 12:52 AM, Andy Lutomirski <l...@kernel.org> wrote: > Due to a blatant design error, SYSENTER doesn't clear TF. As a result, > if a user does SYSENTER with TF set, we will single-step through the > kernel until something clears TF. There is absolutely nothing we can > do to prevent this short of turning off SYSENTER [1]. > > Simplify the handling considerably with two changes: > > 1. We already sanitize EFLAGS in SYSENTER to clear NT and AC. We can > add TF to that list of flags to sanitize with no overhead whatsoever. > > 2. Teach do_debug to ignore single-step traps in the SYSENTER prologue.
What is wrong with the current method of clearing TF and setting TIF_SINGLESTEP on the first debug trap? This patch actually increases complexity because it has to check for a range of addresses rather than just the first instruction, plus it has to singlestep all the way through the SYSENTER prologue. Unless there is an actual issue with TIF_SINGLESTEP, I don't think this patch is an improvement. -- Brian Gerst
