| Message ID | 20210928230946.4062144-3-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | bpf: Build with -Wcast-function-type | expand |
On Tue, Sep 28, 2021 at 04:09:46PM -0700, Kees Cook wrote: > In order to keep ahead of cases in the kernel where Control Flow > Integrity (CFI) may trip over function call casts, enabling > -Wcast-function-type is helpful. To that end, BPF_CAST_CALL causes > various warnings and is one of the last places in the kernel > triggering this warning. > > For actual function calls, replace BPF_CAST_CALL() with a typedef, which > captures the same details about the given function pointers. > > This change results in no object code difference. > > Cc: Alexei Starovoitov <ast@kernel.org> > Cc: Daniel Borkmann <daniel@iogearbox.net> > Cc: Martin KaFai Lau <kafai@fb.com> > Cc: Song Liu <songliubraving@fb.com> > Cc: Yonghong Song <yhs@fb.com> > Cc: John Fastabend <john.fastabend@gmail.com> > Cc: KP Singh <kpsingh@kernel.org> > Cc: netdev@vger.kernel.org > Cc: bpf@vger.kernel.org > Cc: Gustavo A. R. Silva <gustavoars@kernel.org> > Link: https://github.com/KSPP/linux/issues/20 > Signed-off-by: Kees Cook <keescook@chromium.org> > Acked-by: Andrii Nakryiko <andrii@kernel.org> > Link: https://lore.kernel.org/lkml/CAEf4Bzb46=-J5Fxc3mMZ8JQPtK1uoE0q6+g6WPz53Cvx=CBEhw@mail.gmail.com Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org> Thanks -- Gustavo > --- > include/linux/bpf.h | 4 +++- > include/linux/filter.h | 5 ----- > kernel/bpf/arraymap.c | 7 +++---- > kernel/bpf/hashtab.c | 7 +++---- > kernel/bpf/helpers.c | 5 ++--- > 5 files changed, 11 insertions(+), 17 deletions(-) > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index b6c45a6cbbba..19735d59230a 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -48,6 +48,7 @@ extern struct idr btf_idr; > extern spinlock_t btf_idr_lock; > extern struct kobject *btf_kobj; > > +typedef u64 (*bpf_callback_t)(u64, u64, u64, u64, u64); > typedef int (*bpf_iter_init_seq_priv_t)(void *private_data, > struct bpf_iter_aux_info *aux); > typedef void (*bpf_iter_fini_seq_priv_t)(void *private_data); > @@ -142,7 +143,8 @@ struct bpf_map_ops { > int (*map_set_for_each_callback_args)(struct bpf_verifier_env *env, > struct bpf_func_state *caller, > struct bpf_func_state *callee); > - int (*map_for_each_callback)(struct bpf_map *map, void *callback_fn, > + int (*map_for_each_callback)(struct bpf_map *map, > + bpf_callback_t callback_fn, > void *callback_ctx, u64 flags); > > /* BTF name and id of struct allocated by map_alloc */ > diff --git a/include/linux/filter.h b/include/linux/filter.h > index 6c247663d4ce..47f80adbe744 100644 > --- a/include/linux/filter.h > +++ b/include/linux/filter.h > @@ -360,11 +360,6 @@ static inline bool insn_is_zext(const struct bpf_insn *insn) > .off = 0, \ > .imm = TGT }) > > -/* Function call */ > - > -#define BPF_CAST_CALL(x) \ > - ((u64 (*)(u64, u64, u64, u64, u64))(x)) > - > /* Convert function address to BPF immediate */ > > #define BPF_CALL_IMM(x) ((void *)(x) - (void *)__bpf_call_base) > diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c > index cebd4fb06d19..5e1ccfae916b 100644 > --- a/kernel/bpf/arraymap.c > +++ b/kernel/bpf/arraymap.c > @@ -645,7 +645,7 @@ static const struct bpf_iter_seq_info iter_seq_info = { > .seq_priv_size = sizeof(struct bpf_iter_seq_array_map_info), > }; > > -static int bpf_for_each_array_elem(struct bpf_map *map, void *callback_fn, > +static int bpf_for_each_array_elem(struct bpf_map *map, bpf_callback_t callback_fn, > void *callback_ctx, u64 flags) > { > u32 i, key, num_elems = 0; > @@ -668,9 +668,8 @@ static int bpf_for_each_array_elem(struct bpf_map *map, void *callback_fn, > val = array->value + array->elem_size * i; > num_elems++; > key = i; > - ret = BPF_CAST_CALL(callback_fn)((u64)(long)map, > - (u64)(long)&key, (u64)(long)val, > - (u64)(long)callback_ctx, 0); > + ret = callback_fn((u64)(long)map, (u64)(long)&key, > + (u64)(long)val, (u64)(long)callback_ctx, 0); > /* return value: 0 - continue, 1 - stop and return */ > if (ret) > break; > diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c > index 3d8f9d6997d5..d29af9988f37 100644 > --- a/kernel/bpf/hashtab.c > +++ b/kernel/bpf/hashtab.c > @@ -2049,7 +2049,7 @@ static const struct bpf_iter_seq_info iter_seq_info = { > .seq_priv_size = sizeof(struct bpf_iter_seq_hash_map_info), > }; > > -static int bpf_for_each_hash_elem(struct bpf_map *map, void *callback_fn, > +static int bpf_for_each_hash_elem(struct bpf_map *map, bpf_callback_t callback_fn, > void *callback_ctx, u64 flags) > { > struct bpf_htab *htab = container_of(map, struct bpf_htab, map); > @@ -2089,9 +2089,8 @@ static int bpf_for_each_hash_elem(struct bpf_map *map, void *callback_fn, > val = elem->key + roundup_key_size; > } > num_elems++; > - ret = BPF_CAST_CALL(callback_fn)((u64)(long)map, > - (u64)(long)key, (u64)(long)val, > - (u64)(long)callback_ctx, 0); > + ret = callback_fn((u64)(long)map, (u64)(long)key, > + (u64)(long)val, (u64)(long)callback_ctx, 0); > /* return value: 0 - continue, 1 - stop and return */ > if (ret) { > rcu_read_unlock(); > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > index 2c604ff8c7fb..1ffd469c217f 100644 > --- a/kernel/bpf/helpers.c > +++ b/kernel/bpf/helpers.c > @@ -1056,7 +1056,7 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer) > struct bpf_hrtimer *t = container_of(hrtimer, struct bpf_hrtimer, timer); > struct bpf_map *map = t->map; > void *value = t->value; > - void *callback_fn; > + bpf_callback_t callback_fn; > void *key; > u32 idx; > > @@ -1081,8 +1081,7 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer) > key = value - round_up(map->key_size, 8); > } > > - BPF_CAST_CALL(callback_fn)((u64)(long)map, (u64)(long)key, > - (u64)(long)value, 0, 0); > + callback_fn((u64)(long)map, (u64)(long)key, (u64)(long)value, 0, 0); > /* The verifier checked that return value is zero. */ > > this_cpu_write(hrtimer_running, NULL); > -- > 2.30.2 >
From: Kees Cook > Sent: 29 September 2021 00:10 ... > In order to keep ahead of cases in the kernel where Control Flow > Integrity (CFI) may trip over function call casts, enabling > -Wcast-function-type is helpful. To that end, BPF_CAST_CALL causes > various warnings and is one of the last places in the kernel > triggering this warning. ... > -static int bpf_for_each_array_elem(struct bpf_map *map, void *callback_fn, > +static int bpf_for_each_array_elem(struct bpf_map *map, bpf_callback_t callback_fn, > void *callback_ctx, u64 flags) > { > u32 i, key, num_elems = 0; > @@ -668,9 +668,8 @@ static int bpf_for_each_array_elem(struct bpf_map *map, void *callback_fn, > val = array->value + array->elem_size * i; > num_elems++; > key = i; > - ret = BPF_CAST_CALL(callback_fn)((u64)(long)map, > - (u64)(long)&key, (u64)(long)val, > - (u64)(long)callback_ctx, 0); > + ret = callback_fn((u64)(long)map, (u64)(long)&key, > + (u64)(long)val, (u64)(long)callback_ctx, 0); > /* return value: 0 - continue, 1 - stop and return */ > if (ret) > break; This is still entirely horrid and potentially error prone. While a callback function seems a nice idea the code is almost always better and much easier to read if some kind of iterator function is used so that the calling code is just a simple loop. This is true even if you need a #define for the loop end. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index b6c45a6cbbba..19735d59230a 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -48,6 +48,7 @@ extern struct idr btf_idr; extern spinlock_t btf_idr_lock; extern struct kobject *btf_kobj; +typedef u64 (*bpf_callback_t)(u64, u64, u64, u64, u64); typedef int (*bpf_iter_init_seq_priv_t)(void *private_data, struct bpf_iter_aux_info *aux); typedef void (*bpf_iter_fini_seq_priv_t)(void *private_data); @@ -142,7 +143,8 @@ struct bpf_map_ops { int (*map_set_for_each_callback_args)(struct bpf_verifier_env *env, struct bpf_func_state *caller, struct bpf_func_state *callee); - int (*map_for_each_callback)(struct bpf_map *map, void *callback_fn, + int (*map_for_each_callback)(struct bpf_map *map, + bpf_callback_t callback_fn, void *callback_ctx, u64 flags); /* BTF name and id of struct allocated by map_alloc */ diff --git a/include/linux/filter.h b/include/linux/filter.h index 6c247663d4ce..47f80adbe744 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -360,11 +360,6 @@ static inline bool insn_is_zext(const struct bpf_insn *insn) .off = 0, \ .imm = TGT }) -/* Function call */ - -#define BPF_CAST_CALL(x) \ - ((u64 (*)(u64, u64, u64, u64, u64))(x)) - /* Convert function address to BPF immediate */ #define BPF_CALL_IMM(x) ((void *)(x) - (void *)__bpf_call_base) diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c index cebd4fb06d19..5e1ccfae916b 100644 --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -645,7 +645,7 @@ static const struct bpf_iter_seq_info iter_seq_info = { .seq_priv_size = sizeof(struct bpf_iter_seq_array_map_info), }; -static int bpf_for_each_array_elem(struct bpf_map *map, void *callback_fn, +static int bpf_for_each_array_elem(struct bpf_map *map, bpf_callback_t callback_fn, void *callback_ctx, u64 flags) { u32 i, key, num_elems = 0; @@ -668,9 +668,8 @@ static int bpf_for_each_array_elem(struct bpf_map *map, void *callback_fn, val = array->value + array->elem_size * i; num_elems++; key = i; - ret = BPF_CAST_CALL(callback_fn)((u64)(long)map, - (u64)(long)&key, (u64)(long)val, - (u64)(long)callback_ctx, 0); + ret = callback_fn((u64)(long)map, (u64)(long)&key, + (u64)(long)val, (u64)(long)callback_ctx, 0); /* return value: 0 - continue, 1 - stop and return */ if (ret) break; diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index 3d8f9d6997d5..d29af9988f37 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -2049,7 +2049,7 @@ static const struct bpf_iter_seq_info iter_seq_info = { .seq_priv_size = sizeof(struct bpf_iter_seq_hash_map_info), }; -static int bpf_for_each_hash_elem(struct bpf_map *map, void *callback_fn, +static int bpf_for_each_hash_elem(struct bpf_map *map, bpf_callback_t callback_fn, void *callback_ctx, u64 flags) { struct bpf_htab *htab = container_of(map, struct bpf_htab, map); @@ -2089,9 +2089,8 @@ static int bpf_for_each_hash_elem(struct bpf_map *map, void *callback_fn, val = elem->key + roundup_key_size; } num_elems++; - ret = BPF_CAST_CALL(callback_fn)((u64)(long)map, - (u64)(long)key, (u64)(long)val, - (u64)(long)callback_ctx, 0); + ret = callback_fn((u64)(long)map, (u64)(long)key, + (u64)(long)val, (u64)(long)callback_ctx, 0); /* return value: 0 - continue, 1 - stop and return */ if (ret) { rcu_read_unlock(); diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 2c604ff8c7fb..1ffd469c217f 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1056,7 +1056,7 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer) struct bpf_hrtimer *t = container_of(hrtimer, struct bpf_hrtimer, timer); struct bpf_map *map = t->map; void *value = t->value; - void *callback_fn; + bpf_callback_t callback_fn; void *key; u32 idx; @@ -1081,8 +1081,7 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer) key = value - round_up(map->key_size, 8); } - BPF_CAST_CALL(callback_fn)((u64)(long)map, (u64)(long)key, - (u64)(long)value, 0, 0); + callback_fn((u64)(long)map, (u64)(long)key, (u64)(long)value, 0, 0); /* The verifier checked that return value is zero. */ this_cpu_write(hrtimer_running, NULL);