On Tue, 26 Jun 2018, Andy Lutomirski wrote: > > On Jun 26, 2018, at 2:16 PM, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote: > > > > Make the behavior rseq on compat tasks more robust by ensuring that > > kernel/rseq.c:rseq_get_rseq_cs() clears the high bits of > > rseq_cs->abort_ip, rseq_cs->start_ip and rseq_cs->post_commit_offset > > when a 32-bit binary is run on a 64-bit kernel. > > > > The intent here is that if user-space has garbage rather than zeroes > > in its struct rseq_cs fields padding, the behavior will be the same > > whether the binary is run on 32-bit or 64-bit kernels. > > > > Use in_compat_syscall() when rseq_get_rseq_cs() is invoked from > > system call context, and use is_compat_frame() when invoked from > > signal delivery. > > > > And when it’s invoked due to preemption unrelated to a syscall or signal, > you malfunction? > > I think the only sane solution is to make these fields be u64, delete the > LINUX_FIELD_ macros, and possibly teach the x86 slowpath return to inject > a signal if it’s trying to return to a 32-bit context with garbage in the > high bits of regs->ip so that we determistically fail if the user screws > up. Right. That's the only sane solution. Trying to play games with 32/64bit for a dubious value is going to bite us within no time and just create ugly workarounds left and right. Forcing a clear handling upfront avoids all of that. Thanks, tglx
