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From:   Kalesh Singh <kaleshsingh@google.com>
Date:   Wed, 13 Oct 2021 18:39:42 -0700
Message-ID: <CAC_TJverUnJVTGRw1pg1ughJ5YDA8Yo-fkpAm=_fWq9fdAgqTw@mail.gmail.com>
Subject: Re: [PATCH] tracing/cfi: Fix cmp_entries_* functions signature mismatch
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Suren Baghdasaryan <surenb@google.com>,
        Hridya Valsaraju <hridya@google.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        "Cc: Android Kernel" <kernel-team@android.com>,
        Ingo Molnar <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Oct 13, 2021 at 3:08 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Thu, 23 Sep 2021 17:09:07 +0000
> Kalesh Singh <kaleshsingh@google.com> wrote:
>
>
> This finally popped up into my queue (from all my traveling and running of
> conferences :-p )
>
>
> > If CONFIG_CFI_CLANG=y, attempting to read an event histogram will cause
> > the kernel to panic due to failed CFI check.
> >
> >     1. echo 'hist:keys=common_pid' >> events/sched/sched_switch/trigger
> >     2. cat >> events/sched/sched_switch/hist
>
> Do you mean:
>
>           2. cat events/sched/sched_switch/hist
>
> ?
>
> Small nits below.

Thanks Steve, v2 posted at
https://lore.kernel.org/r/20211014013704.2854890-1-kaleshsingh@google.com/

- Kalesh
>
> >     3. kernel panices on attempting to read hist
> >
> > This happens because the sort() function expects a generic
> > int (*)(const void *, const void *) pointer for the compare function.
> > To prevent this CFI failure, change tracing map cmp_entries_* function
> > signatures to match this.
> >
> > Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> > ---
> >  kernel/trace/tracing_map.c | 40 ++++++++++++++++++++++----------------
> >  1 file changed, 23 insertions(+), 17 deletions(-)
> >
> > diff --git a/kernel/trace/tracing_map.c b/kernel/trace/tracing_map.c
> > index d6bddb157ef2..a8c80ebbf9da 100644
> > --- a/kernel/trace/tracing_map.c
> > +++ b/kernel/trace/tracing_map.c
> > @@ -834,19 +834,21 @@ int tracing_map_init(struct tracing_map *map)
> >       return err;
> >  }
> >
> > -static int cmp_entries_dup(const struct tracing_map_sort_entry **a,
> > -                        const struct tracing_map_sort_entry **b)
> > +static int cmp_entries_dup(const void *__a, const void *__b)
>
> Instead of __a and __b, have it as:
>
>         const void *A, const void *B
>
>
> >  {
> >       int ret = 0;
> > +     const struct tracing_map_sort_entry *a
> > +             = *(const struct tracing_map_sort_entry **)__a;
> > +     const struct tracing_map_sort_entry *b
> > +             = *(const struct tracing_map_sort_entry **)__b;
>
> Please put these before the ret, we like to have a "upside down xmas tree"
> type of declaration, where longer lines come before shorter ones. Also,
> this can be "prettified" as:
>
>         const struct tracing_map_sort_entry **pa = A;
>         const struct tracing_map_sort_entry **pb = B;
>         const struct tracing_map_sort_entry *a = *pa;
>         const struct tracing_map_sort_entry *b = *pb;
>         int ret = 0;
>
> >
> > -     if (memcmp((*a)->key, (*b)->key, (*a)->elt->map->key_size))
> > +     if (memcmp(a->key, b->key, a->elt->map->key_size))
> >               ret = 1;
> >
> >       return ret;
> >  }
> >
> > -static int cmp_entries_sum(const struct tracing_map_sort_entry **a,
> > -                        const struct tracing_map_sort_entry **b)
> > +static int cmp_entries_sum(const void *__a, const void *__b)
> >  {
> >       const struct tracing_map_elt *elt_a, *elt_b;
> >       struct tracing_map_sort_key *sort_key;
> > @@ -854,9 +856,13 @@ static int cmp_entries_sum(const struct tracing_map_sort_entry **a,
> >       tracing_map_cmp_fn_t cmp_fn;
> >       void *val_a, *val_b;
> >       int ret = 0;
> > +     const struct tracing_map_sort_entry *a
> > +             = *(const struct tracing_map_sort_entry **)__a;
> > +     const struct tracing_map_sort_entry *b
> > +             = *(const struct tracing_map_sort_entry **)__b;
>
> Same here.
>
> >
> > -     elt_a = (*a)->elt;
> > -     elt_b = (*b)->elt;
> > +     elt_a = a->elt;
> > +     elt_b = b->elt;
> >
> >       sort_key = &elt_a->map->sort_key;
> >
> > @@ -873,8 +879,7 @@ static int cmp_entries_sum(const struct tracing_map_sort_entry **a,
> >       return ret;
> >  }
> >
> > -static int cmp_entries_key(const struct tracing_map_sort_entry **a,
> > -                        const struct tracing_map_sort_entry **b)
> > +static int cmp_entries_key(const void *__a, const void *__b)
> >  {
> >       const struct tracing_map_elt *elt_a, *elt_b;
> >       struct tracing_map_sort_key *sort_key;
> > @@ -882,9 +887,13 @@ static int cmp_entries_key(const struct tracing_map_sort_entry **a,
> >       tracing_map_cmp_fn_t cmp_fn;
> >       void *val_a, *val_b;
> >       int ret = 0;
> > +     const struct tracing_map_sort_entry *a
> > +             = *(const struct tracing_map_sort_entry **)__a;
> > +     const struct tracing_map_sort_entry *b
> > +             = *(const struct tracing_map_sort_entry **)__b;
>
> And here.
>
> Thanks, and sorry for the long delay.
>
> -- Steve
>
> >
> > -     elt_a = (*a)->elt;
> > -     elt_b = (*b)->elt;
> > +     elt_a = a->elt;
> > +     elt_b = b->elt;
> >
> >       sort_key = &elt_a->map->sort_key;
> >
> > @@ -989,10 +998,8 @@ static void sort_secondary(struct tracing_map *map,
> >                          struct tracing_map_sort_key *primary_key,
> >                          struct tracing_map_sort_key *secondary_key)
> >  {
> > -     int (*primary_fn)(const struct tracing_map_sort_entry **,
> > -                       const struct tracing_map_sort_entry **);
> > -     int (*secondary_fn)(const struct tracing_map_sort_entry **,
> > -                         const struct tracing_map_sort_entry **);
> > +     int (*primary_fn)(const void *, const void *);
> > +     int (*secondary_fn)(const void *, const void *);
> >       unsigned i, start = 0, n_sub = 1;
> >
> >       if (is_key(map, primary_key->field_idx))
> > @@ -1061,8 +1068,7 @@ int tracing_map_sort_entries(struct tracing_map *map,
> >                            unsigned int n_sort_keys,
> >                            struct tracing_map_sort_entry ***sort_entries)
> >  {
> > -     int (*cmp_entries_fn)(const struct tracing_map_sort_entry **,
> > -                           const struct tracing_map_sort_entry **);
> > +     int (*cmp_entries_fn)(const void *, const void *);
> >       struct tracing_map_sort_entry *sort_entry, **entries;
> >       int i, n_entries, ret;
> >
> >
> > base-commit: 58e2cf5d794616b84f591d4d1276c8953278ce24
>