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Message-ID: <CABCJKucTiHDitevf1U97eCV1KdxAyui+fWvD1i7c8piVMnmjoQ@mail.gmail.com>
Date: Fri, 24 Sep 2021 08:20:35 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Kalesh Singh <kaleshsingh@...gle.com>
Cc: 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
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>
Sami
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