Re: [PATCH 1/2] x86/hw_breakpoint: Prevent data breakpoints on __per_cpu_offset

[Andy Lutomirski]

On Thu, Feb 4, 2021 at 6:26 AM Lai Jiangshan <jiangshanlai@xxxxxxxxx> wrote:
>
> From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
>
> When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU
> GSBASE value via __per_cpu_offset or pcpu_unit_offsets.
>
> When data breakpoint is set on __per_cpu_offset[cpu] (read-write
> operation), the specific cpu will be stuck in the infinite #DB loop.
> RCU will try to send NMI to the specific cpu, but it is not working
> either since NMI also relies on paranoid_entry().

Should we consider having a .percpu..noinstr section and having
objtool enforce this?