Messages in this thread | | | Subject | Re: [RFC PATCH for 4.18 2/2] rseq: compat: clear high bits of rseq_cs fields | From | Andy Lutomirski <> | Date | Tue, 26 Jun 2018 14:58:08 -0700 |
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> On Jun 26, 2018, at 2:16 PM, Mathieu Desnoyers <mathieu.desnoyers@efficios.com> 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.
Rseq is brand new. It should not need compat code at all.
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