From 3d717fad5081b8e3bda76d86907fad95398cbde8 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Tue, 28 Sep 2021 16:09:45 -0700
Subject: [PATCH 1/2] bpf: Replace "want address" users of BPF_CAST_CALL with
BPF_CALL_IMM
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.
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://github.com/KSPP/linux/issues/20
Link: https://lore.kernel.org/lkml/CAEf4Bzb46=-J5Fxc3mMZ8JQPtK1uoE0q6+g6WPz53Cvx=CBEhw@mail.gmail.com
Link: https://lore.kernel.org/bpf/20210928230946.4062144-2-keescook@chromium.org
---
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 4a93c12543ee2..6c247663d4ce9 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 32471ba027086..3d8f9d6997d52 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 7a8351604f670..1433752db7403 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 08f438e6fe9e2..21ea1ab253a19 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;
From 102acbacfd9a96d101abd96d1a7a5bf92b7c3e8e Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Tue, 28 Sep 2021 16:09:46 -0700
Subject: [PATCH 2/2] bpf: Replace callers of BPF_CAST_CALL with proper
function typedef
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.
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://github.com/KSPP/linux/issues/20
Link: https://lore.kernel.org/lkml/CAEf4Bzb46=-J5Fxc3mMZ8JQPtK1uoE0q6+g6WPz53Cvx=CBEhw@mail.gmail.com
Link: https://lore.kernel.org/bpf/20210928230946.4062144-3-keescook@chromium.org
---
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 b6c45a6cbbbaf..19735d59230ad 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 6c247663d4ce9..47f80adbe7447 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 cebd4fb06d190..5e1ccfae916b9 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 3d8f9d6997d52..d29af9988f37a 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 2c604ff8c7fb9..1ffd469c217fa 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);