Re: [PATCH bpf-next] bpf: Inherit system settings for CPU security mitigations

[Yafang Shao <laoar.shao@gmail.com>]

On Fri, Oct 20, 2023 at 8:42 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Thu, Oct 5, 2023 at 1:41 AM Yafang Shao <laoar.shao@gmail.com> wrote:
> >
> > Currently, there exists a system-wide setting related to CPU security
> > mitigations, denoted as 'mitigations='. When set to 'mitigations=off', it
> > deactivates all optional CPU mitigations. Therefore, if we implement a
> > system-wide 'mitigations=off' setting, it should inherently bypass Spectre
> > v1 and Spectre v4 in the BPF subsystem.
> >
> > Please note that there is also a 'nospectre_v1' setting on x86 and ppc
> > architectures, though it is not currently exported. For the time being,
> > let's disregard it.
> >
> > This idea emerged during our discussion about potential Spectre v1 attacks
> > with Luis[1].
> >
> > [1]. https://lore.kernel.org/bpf/b4fc15f7-b204-767e-ebb9-fdb4233961fb@iogearbox.net/
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > Cc: Luis Gerhorst <gerhorst@cs.fau.de>
> > ---
> >  include/linux/bpf.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index a82efd34b741..61bde4520f5c 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -2164,12 +2164,12 @@ static inline bool bpf_allow_uninit_stack(void)
> >
> >  static inline bool bpf_bypass_spec_v1(void)
> >  {
> > -       return perfmon_capable();
> > +       return perfmon_capable() || cpu_mitigations_off();
> >  }
> >
> >  static inline bool bpf_bypass_spec_v4(void)
> >  {
> > -       return perfmon_capable();
> > +       return perfmon_capable() || cpu_mitigations_off();
> >  }
>
> Yafang,
>
> this patch breaks several
> test_progs -t verifier

Sorry, I miss that.

>
> tests when system is booted with mitigations=off command line.
>
> Please follow up with a patch to fix this.

will do it.

>
> As you noticed cpu_mitigations_off() is not quite right here.
> The system might have booted without that command line, but
> spec_v1 and spec_v4 mitigations are turned off.
> Unfortunately there is no good way to check that atm.
> Have you seen this patch set ?
> https://lore.kernel.org/all/20231019181158.1982205-1-leitao@debian.org/
> Please take a look at it and comment if you think it will help.

Thanks for your information. will take a look.

>
> In the meantime please fix test_progs -t verifier

sure

-- 
Regards
Yafang