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Message-ID: <CAC_TJve2aS_tHfmMCsayPFrAPaMid5DU3NK82KXC3dB9vhPdpw@mail.gmail.com>
Date: Mon, 27 Sep 2021 11:15:01 -0700
From: Kalesh Singh <kaleshsingh@...gle.com>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
Hridya Valsaraju <hridya@...gle.com>, namhyung@...nel.org,
Nick Desaulniers <ndesaulniers@...gle.com>,
Android Kernel Team <kernel-team@...roid.com>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/cfi: Fix cmp_entries_* functions signature mismatch
On Fri, Sep 24, 2021 at 8:20 AM Sami Tolvanen <samitolvanen@...gle.com> wrote:
>
> Hi Kalesh,
>
> On Thu, Sep 23, 2021 at 10:09 AM Kalesh Singh <kaleshsingh@...gle.com> wrote:
> >
> > 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
> > 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@...gle.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)
> > {
> > 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;
> >
> > - 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;
> >
> > - 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;
> >
> > - 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;
> >
> >
>
> Thanks for the patch! This looks correct to me and fixes the function
> type mismatch that trips CFI.
>
> Reviewed-by: Sami Tolvanen <samitolvanen@...gle.com>
Thanks for the review Sami.
Steve, will this get picked up for your tree?
>
> Sami
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