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* [PATCH bpf-next v2 0/2] bpf: Build with -Wcast-function-type
@ 2021-09-28 23:09 Kees Cook
  2021-09-28 23:09 ` [PATCH bpf-next v2 1/2] bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM Kees Cook
                   ` (2 more replies)
  0 siblings, 3 replies; 7+ messages in thread
From: Kees Cook @ 2021-09-28 23:09 UTC (permalink / raw)
  To: Alexei Starovoitov
  Cc: Kees Cook, Daniel Borkmann, Andrii Nakryiko, Martin KaFai Lau,
	Song Liu, Yonghong Song, John Fastabend, KP Singh, linux-kernel,
	netdev, bpf, linux-hardening

Hi,

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, replace BPF_CAST_CALL() as it triggers warnings
with this option and is now one of the last places in the kernel in need
of fixing.

Thanks,

-Kees

v2:
- rebase to bpf-next
- add acks
v1: https://lore.kernel.org/lkml/20210927182700.2980499-1-keescook@chromium.org

Kees Cook (2):
  bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM
  bpf: Replace callers of BPF_CAST_CALL with proper function typedef

 include/linux/bpf.h    |  4 +++-
 include/linux/filter.h |  7 +++----
 kernel/bpf/arraymap.c  |  7 +++----
 kernel/bpf/hashtab.c   | 13 ++++++-------
 kernel/bpf/helpers.c   |  5 ++---
 kernel/bpf/verifier.c  | 26 +++++++++-----------------
 lib/test_bpf.c         |  2 +-
 7 files changed, 27 insertions(+), 37 deletions(-)

-- 
2.30.2


^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH bpf-next v2 1/2] bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM
  2021-09-28 23:09 [PATCH bpf-next v2 0/2] bpf: Build with -Wcast-function-type Kees Cook
@ 2021-09-28 23:09 ` Kees Cook
  2021-09-28 23:25   ` Gustavo A. R. Silva
  2021-09-28 23:09 ` [PATCH bpf-next v2 2/2] bpf: Replace callers of BPF_CAST_CALL with proper function typedef Kees Cook
  2021-09-28 23:33 ` [PATCH bpf-next v2 0/2] bpf: Build with -Wcast-function-type Alexei Starovoitov
  2 siblings, 1 reply; 7+ messages in thread
From: Kees Cook @ 2021-09-28 23:09 UTC (permalink / raw)
  To: Alexei Starovoitov
  Cc: Kees Cook, Daniel Borkmann, Martin KaFai Lau, Song Liu,
	Yonghong Song, John Fastabend, KP Singh, netdev, bpf,
	Gustavo A . R . Silva, Andrii Nakryiko, linux-kernel,
	linux-hardening

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.

Most places using BPF_CAST_CALL actually just want a void * to perform
math on. It's not actually performing a call, so just use a different
helper to get the void *, by way of the new BPF_CALL_IMM() helper, which
can clean up a common copy/paste idiom as well.

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
---
 include/linux/filter.h |  6 +++++-
 kernel/bpf/hashtab.c   |  6 +++---
 kernel/bpf/verifier.c  | 26 +++++++++-----------------
 lib/test_bpf.c         |  2 +-
 4 files changed, 18 insertions(+), 22 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 4a93c12543ee..6c247663d4ce 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -365,13 +365,17 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
 #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)
+
 #define BPF_EMIT_CALL(FUNC)					\
 	((struct bpf_insn) {					\
 		.code  = BPF_JMP | BPF_CALL,			\
 		.dst_reg = 0,					\
 		.src_reg = 0,					\
 		.off   = 0,					\
-		.imm   = ((FUNC) - __bpf_call_base) })
+		.imm   = BPF_CALL_IMM(FUNC) })
 
 /* Raw code statement block */
 
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 32471ba02708..3d8f9d6997d5 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -668,7 +668,7 @@ static int htab_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
 
 	BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
 		     (void *(*)(struct bpf_map *map, void *key))NULL));
-	*insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
+	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
 	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 1);
 	*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
 				offsetof(struct htab_elem, key) +
@@ -709,7 +709,7 @@ static int htab_lru_map_gen_lookup(struct bpf_map *map,
 
 	BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
 		     (void *(*)(struct bpf_map *map, void *key))NULL));
-	*insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
+	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
 	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 4);
 	*insn++ = BPF_LDX_MEM(BPF_B, ref_reg, ret,
 			      offsetof(struct htab_elem, lru_node) +
@@ -2397,7 +2397,7 @@ static int htab_of_map_gen_lookup(struct bpf_map *map,
 
 	BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
 		     (void *(*)(struct bpf_map *map, void *key))NULL));
-	*insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
+	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
 	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 2);
 	*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
 				offsetof(struct htab_elem, key) +
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7a8351604f67..1433752db740 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1744,7 +1744,7 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id)
 
 	desc = &tab->descs[tab->nr_descs++];
 	desc->func_id = func_id;
-	desc->imm = BPF_CAST_CALL(addr) - __bpf_call_base;
+	desc->imm = BPF_CALL_IMM(addr);
 	err = btf_distill_func_proto(&env->log, btf_vmlinux,
 				     func_proto, func_name,
 				     &desc->func_model);
@@ -12514,8 +12514,7 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 			if (!bpf_pseudo_call(insn))
 				continue;
 			subprog = insn->off;
-			insn->imm = BPF_CAST_CALL(func[subprog]->bpf_func) -
-				    __bpf_call_base;
+			insn->imm = BPF_CALL_IMM(func[subprog]->bpf_func);
 		}
 
 		/* we use the aux data to keep a list of the start addresses
@@ -12995,32 +12994,25 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 patch_map_ops_generic:
 			switch (insn->imm) {
 			case BPF_FUNC_map_lookup_elem:
-				insn->imm = BPF_CAST_CALL(ops->map_lookup_elem) -
-					    __bpf_call_base;
+				insn->imm = BPF_CALL_IMM(ops->map_lookup_elem);
 				continue;
 			case BPF_FUNC_map_update_elem:
-				insn->imm = BPF_CAST_CALL(ops->map_update_elem) -
-					    __bpf_call_base;
+				insn->imm = BPF_CALL_IMM(ops->map_update_elem);
 				continue;
 			case BPF_FUNC_map_delete_elem:
-				insn->imm = BPF_CAST_CALL(ops->map_delete_elem) -
-					    __bpf_call_base;
+				insn->imm = BPF_CALL_IMM(ops->map_delete_elem);
 				continue;
 			case BPF_FUNC_map_push_elem:
-				insn->imm = BPF_CAST_CALL(ops->map_push_elem) -
-					    __bpf_call_base;
+				insn->imm = BPF_CALL_IMM(ops->map_push_elem);
 				continue;
 			case BPF_FUNC_map_pop_elem:
-				insn->imm = BPF_CAST_CALL(ops->map_pop_elem) -
-					    __bpf_call_base;
+				insn->imm = BPF_CALL_IMM(ops->map_pop_elem);
 				continue;
 			case BPF_FUNC_map_peek_elem:
-				insn->imm = BPF_CAST_CALL(ops->map_peek_elem) -
-					    __bpf_call_base;
+				insn->imm = BPF_CALL_IMM(ops->map_peek_elem);
 				continue;
 			case BPF_FUNC_redirect_map:
-				insn->imm = BPF_CAST_CALL(ops->map_redirect) -
-					    __bpf_call_base;
+				insn->imm = BPF_CALL_IMM(ops->map_redirect);
 				continue;
 			}
 
diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index 08f438e6fe9e..21ea1ab253a1 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -12439,7 +12439,7 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs)
 					err = -EFAULT;
 					goto out_err;
 				}
-				*insn = BPF_EMIT_CALL(BPF_CAST_CALL(addr));
+				*insn = BPF_EMIT_CALL(addr);
 				if ((long)__bpf_call_base + insn->imm != addr)
 					*insn = BPF_JMP_A(0); /* Skip: NOP */
 				break;
-- 
2.30.2


^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH bpf-next v2 2/2] bpf: Replace callers of BPF_CAST_CALL with proper function typedef
  2021-09-28 23:09 [PATCH bpf-next v2 0/2] bpf: Build with -Wcast-function-type Kees Cook
  2021-09-28 23:09 ` [PATCH bpf-next v2 1/2] bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM Kees Cook
@ 2021-09-28 23:09 ` Kees Cook
  2021-09-28 23:26   ` Gustavo A. R. Silva
  2021-10-02 16:09   ` David Laight
  2021-09-28 23:33 ` [PATCH bpf-next v2 0/2] bpf: Build with -Wcast-function-type Alexei Starovoitov
  2 siblings, 2 replies; 7+ messages in thread
From: Kees Cook @ 2021-09-28 23:09 UTC (permalink / raw)
  To: Alexei Starovoitov
  Cc: Kees Cook, Daniel Borkmann, Martin KaFai Lau, Song Liu,
	Yonghong Song, John Fastabend, KP Singh, netdev, bpf,
	Gustavo A . R . Silva, Andrii Nakryiko, linux-kernel,
	linux-hardening

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
---
 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


^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH bpf-next v2 1/2] bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM
  2021-09-28 23:09 ` [PATCH bpf-next v2 1/2] bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM Kees Cook
@ 2021-09-28 23:25   ` Gustavo A. R. Silva
  0 siblings, 0 replies; 7+ messages in thread
From: Gustavo A. R. Silva @ 2021-09-28 23:25 UTC (permalink / raw)
  To: Kees Cook
  Cc: Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu,
	Yonghong Song, John Fastabend, KP Singh, netdev, bpf,
	Andrii Nakryiko, linux-kernel, linux-hardening

On Tue, Sep 28, 2021 at 04:09:45PM -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.
> 
> Most places using BPF_CAST_CALL actually just want a void * to perform
> math on. It's not actually performing a call, so just use a different
> helper to get the void *, by way of the new BPF_CALL_IMM() helper, which
> can clean up a common copy/paste idiom as well.
> 
> 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

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks
--
Gustavo

> ---
>  include/linux/filter.h |  6 +++++-
>  kernel/bpf/hashtab.c   |  6 +++---
>  kernel/bpf/verifier.c  | 26 +++++++++-----------------
>  lib/test_bpf.c         |  2 +-
>  4 files changed, 18 insertions(+), 22 deletions(-)
> 
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 4a93c12543ee..6c247663d4ce 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -365,13 +365,17 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
>  #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)
> +
>  #define BPF_EMIT_CALL(FUNC)					\
>  	((struct bpf_insn) {					\
>  		.code  = BPF_JMP | BPF_CALL,			\
>  		.dst_reg = 0,					\
>  		.src_reg = 0,					\
>  		.off   = 0,					\
> -		.imm   = ((FUNC) - __bpf_call_base) })
> +		.imm   = BPF_CALL_IMM(FUNC) })
>  
>  /* Raw code statement block */
>  
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index 32471ba02708..3d8f9d6997d5 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -668,7 +668,7 @@ static int htab_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
>  
>  	BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
>  		     (void *(*)(struct bpf_map *map, void *key))NULL));
> -	*insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
> +	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
>  	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 1);
>  	*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
>  				offsetof(struct htab_elem, key) +
> @@ -709,7 +709,7 @@ static int htab_lru_map_gen_lookup(struct bpf_map *map,
>  
>  	BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
>  		     (void *(*)(struct bpf_map *map, void *key))NULL));
> -	*insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
> +	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
>  	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 4);
>  	*insn++ = BPF_LDX_MEM(BPF_B, ref_reg, ret,
>  			      offsetof(struct htab_elem, lru_node) +
> @@ -2397,7 +2397,7 @@ static int htab_of_map_gen_lookup(struct bpf_map *map,
>  
>  	BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
>  		     (void *(*)(struct bpf_map *map, void *key))NULL));
> -	*insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
> +	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
>  	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 2);
>  	*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
>  				offsetof(struct htab_elem, key) +
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 7a8351604f67..1433752db740 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1744,7 +1744,7 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id)
>  
>  	desc = &tab->descs[tab->nr_descs++];
>  	desc->func_id = func_id;
> -	desc->imm = BPF_CAST_CALL(addr) - __bpf_call_base;
> +	desc->imm = BPF_CALL_IMM(addr);
>  	err = btf_distill_func_proto(&env->log, btf_vmlinux,
>  				     func_proto, func_name,
>  				     &desc->func_model);
> @@ -12514,8 +12514,7 @@ static int jit_subprogs(struct bpf_verifier_env *env)
>  			if (!bpf_pseudo_call(insn))
>  				continue;
>  			subprog = insn->off;
> -			insn->imm = BPF_CAST_CALL(func[subprog]->bpf_func) -
> -				    __bpf_call_base;
> +			insn->imm = BPF_CALL_IMM(func[subprog]->bpf_func);
>  		}
>  
>  		/* we use the aux data to keep a list of the start addresses
> @@ -12995,32 +12994,25 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
>  patch_map_ops_generic:
>  			switch (insn->imm) {
>  			case BPF_FUNC_map_lookup_elem:
> -				insn->imm = BPF_CAST_CALL(ops->map_lookup_elem) -
> -					    __bpf_call_base;
> +				insn->imm = BPF_CALL_IMM(ops->map_lookup_elem);
>  				continue;
>  			case BPF_FUNC_map_update_elem:
> -				insn->imm = BPF_CAST_CALL(ops->map_update_elem) -
> -					    __bpf_call_base;
> +				insn->imm = BPF_CALL_IMM(ops->map_update_elem);
>  				continue;
>  			case BPF_FUNC_map_delete_elem:
> -				insn->imm = BPF_CAST_CALL(ops->map_delete_elem) -
> -					    __bpf_call_base;
> +				insn->imm = BPF_CALL_IMM(ops->map_delete_elem);
>  				continue;
>  			case BPF_FUNC_map_push_elem:
> -				insn->imm = BPF_CAST_CALL(ops->map_push_elem) -
> -					    __bpf_call_base;
> +				insn->imm = BPF_CALL_IMM(ops->map_push_elem);
>  				continue;
>  			case BPF_FUNC_map_pop_elem:
> -				insn->imm = BPF_CAST_CALL(ops->map_pop_elem) -
> -					    __bpf_call_base;
> +				insn->imm = BPF_CALL_IMM(ops->map_pop_elem);
>  				continue;
>  			case BPF_FUNC_map_peek_elem:
> -				insn->imm = BPF_CAST_CALL(ops->map_peek_elem) -
> -					    __bpf_call_base;
> +				insn->imm = BPF_CALL_IMM(ops->map_peek_elem);
>  				continue;
>  			case BPF_FUNC_redirect_map:
> -				insn->imm = BPF_CAST_CALL(ops->map_redirect) -
> -					    __bpf_call_base;
> +				insn->imm = BPF_CALL_IMM(ops->map_redirect);
>  				continue;
>  			}
>  
> diff --git a/lib/test_bpf.c b/lib/test_bpf.c
> index 08f438e6fe9e..21ea1ab253a1 100644
> --- a/lib/test_bpf.c
> +++ b/lib/test_bpf.c
> @@ -12439,7 +12439,7 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs)
>  					err = -EFAULT;
>  					goto out_err;
>  				}
> -				*insn = BPF_EMIT_CALL(BPF_CAST_CALL(addr));
> +				*insn = BPF_EMIT_CALL(addr);
>  				if ((long)__bpf_call_base + insn->imm != addr)
>  					*insn = BPF_JMP_A(0); /* Skip: NOP */
>  				break;
> -- 
> 2.30.2
> 

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH bpf-next v2 2/2] bpf: Replace callers of BPF_CAST_CALL with proper function typedef
  2021-09-28 23:09 ` [PATCH bpf-next v2 2/2] bpf: Replace callers of BPF_CAST_CALL with proper function typedef Kees Cook
@ 2021-09-28 23:26   ` Gustavo A. R. Silva
  2021-10-02 16:09   ` David Laight
  1 sibling, 0 replies; 7+ messages in thread
From: Gustavo A. R. Silva @ 2021-09-28 23:26 UTC (permalink / raw)
  To: Kees Cook
  Cc: Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu,
	Yonghong Song, John Fastabend, KP Singh, netdev, bpf,
	Andrii Nakryiko, linux-kernel, linux-hardening

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
> 

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH bpf-next v2 0/2] bpf: Build with -Wcast-function-type
  2021-09-28 23:09 [PATCH bpf-next v2 0/2] bpf: Build with -Wcast-function-type Kees Cook
  2021-09-28 23:09 ` [PATCH bpf-next v2 1/2] bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM Kees Cook
  2021-09-28 23:09 ` [PATCH bpf-next v2 2/2] bpf: Replace callers of BPF_CAST_CALL with proper function typedef Kees Cook
@ 2021-09-28 23:33 ` Alexei Starovoitov
  2 siblings, 0 replies; 7+ messages in thread
From: Alexei Starovoitov @ 2021-09-28 23:33 UTC (permalink / raw)
  To: Kees Cook
  Cc: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
	Martin KaFai Lau, Song Liu, Yonghong Song, John Fastabend,
	KP Singh, LKML, Network Development, bpf, linux-hardening

On Tue, Sep 28, 2021 at 4:09 PM Kees Cook <keescook@chromium.org> wrote:
>
> Hi,
>
> 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, replace BPF_CAST_CALL() as it triggers warnings
> with this option and is now one of the last places in the kernel in need
> of fixing.
>
> Thanks,
>
> -Kees
>
> v2:
> - rebase to bpf-next
> - add acks
> v1: https://lore.kernel.org/lkml/20210927182700.2980499-1-keescook@chromium.org

Applied. Thanks

^ permalink raw reply	[flat|nested] 7+ messages in thread

* RE: [PATCH bpf-next v2 2/2] bpf: Replace callers of BPF_CAST_CALL with proper function typedef
  2021-09-28 23:09 ` [PATCH bpf-next v2 2/2] bpf: Replace callers of BPF_CAST_CALL with proper function typedef Kees Cook
  2021-09-28 23:26   ` Gustavo A. R. Silva
@ 2021-10-02 16:09   ` David Laight
  1 sibling, 0 replies; 7+ messages in thread
From: David Laight @ 2021-10-02 16:09 UTC (permalink / raw)
  To: 'Kees Cook', Alexei Starovoitov
  Cc: Daniel Borkmann, Martin KaFai Lau, Song Liu, Yonghong Song,
	John Fastabend, KP Singh, netdev, bpf, Gustavo A . R . Silva,
	Andrii Nakryiko, linux-kernel, linux-hardening

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)


^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2021-10-02 16:09 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-28 23:09 [PATCH bpf-next v2 0/2] bpf: Build with -Wcast-function-type Kees Cook
2021-09-28 23:09 ` [PATCH bpf-next v2 1/2] bpf: Replace "want address" users of BPF_CAST_CALL with BPF_CALL_IMM Kees Cook
2021-09-28 23:25   ` Gustavo A. R. Silva
2021-09-28 23:09 ` [PATCH bpf-next v2 2/2] bpf: Replace callers of BPF_CAST_CALL with proper function typedef Kees Cook
2021-09-28 23:26   ` Gustavo A. R. Silva
2021-10-02 16:09   ` David Laight
2021-09-28 23:33 ` [PATCH bpf-next v2 0/2] bpf: Build with -Wcast-function-type Alexei Starovoitov

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