Re: [PATCH] perf: check branch sampling priv level in generic code

[Stephane Eranian]

On Tue, May 21, 2013 at 1:08 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Tue, May 21, 2013 at 12:53:37PM +0200, Stephane Eranian wrote:
> >
> > This patch reverts commit 7cc23cd:
> >  perf/x86/intel/lbr: Demand proper privileges for PERF_SAMPLE_BRANCH_KERNEL
> >
> > The check is now implemented in generic code
> > instead of x86 specific code. That way we
> > do not have to repeat the test in each arch
> > supporting branch sampling.
>
> Good point indeed.
>
> > Signed-off-by: Stephane Eranian <eranian@xxxxxxxxxx>
> > ---
> >  arch/x86/kernel/cpu/perf_event_intel_lbr.c |   13 +++----------
> >  kernel/events/core.c                       |    9 ++++-----
> >  2 files changed, 7 insertions(+), 15 deletions(-)
> >
>
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 9dc297f..cf79c81 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -6327,11 +6327,6 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
> >               if (!(mask & ~PERF_SAMPLE_BRANCH_PLM_ALL))
> >                       return -EINVAL;
> >
> > -             /* kernel level capture: check permissions */
> > -             if ((mask & PERF_SAMPLE_BRANCH_PERM_PLM)
> > -                 && perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
> > -                     return -EACCES;
> > -
>
> Oh hey, there was a check..
>
There was a check. But I realized it was broken. It was checking user+kernel.
But it did not cover the case where the priv level which propagated from the
event and was not specific to the branch_sample_type.


>
> >               /* propagate priv level, when not set for branch */
> >               if (!(mask & PERF_SAMPLE_BRANCH_PLM_ALL)) {
> >
> > @@ -6349,6 +6344,10 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
> >                        */
> >                       attr->branch_sample_type = mask;
> >               }
> > +             /* kernel level capture: check permissions */
> > +             if ((mask & PERF_SAMPLE_BRANCH_KERNEL)
> > +                 && perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
> > +                     return -EACCES;
> >       }
> >
> >       if (attr->sample_type & PERF_SAMPLE_REGS_USER) {
> > --
> > 1.7.9.5
> >
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