[PATCH 5.18 0477/1095] bpf: Tag argument to be released in bpf_func_proto

Greg Kroah-Hartman
2022-08-15T21:18:50Z

From: Kumar Kartikeya Dwivedi <memxor@gmail.com>

[ Upstream commit 8f14852e89113d738c99c375b4c8b8b7e1073df1 ]

Add a new type flag for bpf_arg_type that when set tells verifier that
for a release function, that argument's register will be the one for
which meta.ref_obj_id will be set, and which will then be released
using release_reference. To capture the regno, introduce a new field
release_regno in bpf_call_arg_meta.

This would be required in the next patch, where we may either pass NULL
or a refcounted pointer as an argument to the release function
bpf_kptr_xchg. Just releasing only when meta.ref_obj_id is set is not
enough, as there is a case where the type of argument needed matches,
but the ref_obj_id is set to 0. Hence, we must enforce that whenever
meta.ref_obj_id is zero, the register that is to be released can only
be NULL for a release function.

Since we now indicate whether an argument is to be released in
bpf_func_proto itself, is_release_function helper has lost its utitlity,
hence refactor code to work without it, and just rely on
meta.release_regno to know when to release state for a ref_obj_id.
Still, the restriction of one release argument and only one ref_obj_id
passed to BPF helper or kfunc remains. This may be lifted in the future.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220424214901.2743946-3-memxor@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/bpf.h | 5 +-
include/linux/bpf_verifier.h | 3 +-
kernel/bpf/btf.c | 11 ++-
kernel/bpf/ringbuf.c | 4 +-
kernel/bpf/verifier.c | 76 +++++++++++--------
net/core/filter.c | 2 +-
.../selftests/bpf/verifier/ref_tracking.c | 2 +-
tools/testing/selftests/bpf/verifier/sock.c | 6 +-
8 files changed, 60 insertions(+), 49 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 00d55c10d876..2feae4a24d99 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -366,7 +366,10 @@ enum bpf_type_flag {
*/
MEM_PERCPU = BIT(4 + BPF_BASE_TYPE_BITS),

- __BPF_TYPE_LAST_FLAG = MEM_PERCPU,
+ /* Indicates that the argument will be released. */
+ OBJ_RELEASE = BIT(5 + BPF_BASE_TYPE_BITS),
+
+ __BPF_TYPE_LAST_FLAG = OBJ_RELEASE,
};

/* Max number of base types. */
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 3a9d2d7cc6b7..1f1e7f2ea967 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -523,8 +523,7 @@ int check_ptr_off_reg(struct bpf_verifier_env *env,
const struct bpf_reg_state *reg, int regno);
int check_func_arg_reg_off(struct bpf_verifier_env *env,
const struct bpf_reg_state *reg, int regno,
- enum bpf_arg_type arg_type,
- bool is_release_func);
+ enum bpf_arg_type arg_type);
int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
u32 regno);
int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index cbb48eb8c009..752de8112206 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -5994,6 +5994,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
* verifier sees.
*/
for (i = 0; i < nargs; i++) {
+ enum bpf_arg_type arg_type = ARG_DONTCARE;
u32 regno = i + 1;
struct bpf_reg_state *reg = &regs[regno];

@@ -6014,7 +6015,9 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
ref_t = btf_type_skip_modifiers(btf, t->type, &ref_id);
ref_tname = btf_name_by_offset(btf, ref_t->name_off);

- ret = check_func_arg_reg_off(env, reg, regno, ARG_DONTCARE, rel);
+ if (rel && reg->ref_obj_id)
+ arg_type |= OBJ_RELEASE;
+ ret = check_func_arg_reg_off(env, reg, regno, arg_type);
if (ret < 0)
return ret;

@@ -6045,11 +6048,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
if (reg->type == PTR_TO_BTF_ID) {
reg_btf = reg->btf;
reg_ref_id = reg->btf_id;
- /* Ensure only one argument is referenced
- * PTR_TO_BTF_ID, check_func_arg_reg_off relies
- * on only one referenced register being allowed
- * for kfuncs.
- */
+ /* Ensure only one argument is referenced PTR_TO_BTF_ID */
if (reg->ref_obj_id) {
if (ref_obj_id) {
bpf_log(log, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n",
diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index 710ba9de12ce..5173fd37590f 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -404,7 +404,7 @@ BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
const struct bpf_func_proto bpf_ringbuf_submit_proto = {
.func = bpf_ringbuf_submit,
.ret_type = RET_VOID,
- .arg1_type = ARG_PTR_TO_ALLOC_MEM,
+ .arg1_type = ARG_PTR_TO_ALLOC_MEM | OBJ_RELEASE,
.arg2_type = ARG_ANYTHING,
};

@@ -417,7 +417,7 @@ BPF_CALL_2(bpf_ringbuf_discard, void *, sample, u64, flags)
const struct bpf_func_proto bpf_ringbuf_discard_proto = {
.func = bpf_ringbuf_discard,
.ret_type = RET_VOID,
- .arg1_type = ARG_PTR_TO_ALLOC_MEM,
+ .arg1_type = ARG_PTR_TO_ALLOC_MEM | OBJ_RELEASE,
.arg2_type = ARG_ANYTHING,
};

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b8d1060153c8..4f19a86c2682 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -245,6 +245,7 @@ struct bpf_call_arg_meta {
struct bpf_map *map_ptr;
bool raw_mode;
bool pkt_access;
+ u8 release_regno;
int regno;
int access_size;
int mem_size;
@@ -471,17 +472,6 @@ static bool type_may_be_null(u32 type)
return type & PTR_MAYBE_NULL;
}

-/* Determine whether the function releases some resources allocated by another
- * function call. The first reference type argument will be assumed to be
- * released by release_reference().
- */
-static bool is_release_function(enum bpf_func_id func_id)
-{
- return func_id == BPF_FUNC_sk_release ||
- func_id == BPF_FUNC_ringbuf_submit ||
- func_id == BPF_FUNC_ringbuf_discard;
-}
-
static bool may_be_acquire_function(enum bpf_func_id func_id)
{
return func_id == BPF_FUNC_sk_lookup_tcp ||
@@ -5325,6 +5315,11 @@ static bool arg_type_is_int_ptr(enum bpf_arg_type type)
type == ARG_PTR_TO_LONG;
}

+static bool arg_type_is_release(enum bpf_arg_type type)
+{
+ return type & OBJ_RELEASE;
+}
+
static int int_ptr_type_to_size(enum bpf_arg_type type)
{
if (type == ARG_PTR_TO_INT)
@@ -5535,11 +5530,10 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,

int check_func_arg_reg_off(struct bpf_verifier_env *env,
const struct bpf_reg_state *reg, int regno,
- enum bpf_arg_type arg_type,
- bool is_release_func)
+ enum bpf_arg_type arg_type)
{
- bool fixed_off_ok = false, release_reg;
enum bpf_reg_type type = reg->type;
+ bool fixed_off_ok = false;

switch ((u32)type) {
case SCALAR_VALUE:
@@ -5557,7 +5551,7 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env,
/* Some of the argument types nevertheless require a
* zero register offset.
*/
- if (arg_type != ARG_PTR_TO_ALLOC_MEM)
+ if (base_type(arg_type) != ARG_PTR_TO_ALLOC_MEM)
return 0;
break;
/* All the rest must be rejected, except PTR_TO_BTF_ID which allows
@@ -5565,19 +5559,17 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env,
*/
case PTR_TO_BTF_ID:
/* When referenced PTR_TO_BTF_ID is passed to release function,
- * it's fixed offset must be 0. We rely on the property that
- * only one referenced register can be passed to BPF helpers and
- * kfuncs. In the other cases, fixed offset can be non-zero.
+ * it's fixed offset must be 0. In the other cases, fixed offset
+ * can be non-zero.
*/
- release_reg = is_release_func && reg->ref_obj_id;
- if (release_reg && reg->off) {
+ if (arg_type_is_release(arg_type) && reg->off) {
verbose(env, "R%d must have zero offset when passed to release func\n",
regno);
return -EINVAL;
}
- /* For release_reg == true, fixed_off_ok must be false, but we
- * already checked and rejected reg->off != 0 above, so set to
- * true to allow fixed offset for all other cases.
+ /* For arg is release pointer, fixed_off_ok must be false, but
+ * we already checked and rejected reg->off != 0 above, so set
+ * to true to allow fixed offset for all other cases.
*/
fixed_off_ok = true;
break;
@@ -5636,14 +5628,24 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
if (err)
return err;

- err = check_func_arg_reg_off(env, reg, regno, arg_type, is_release_function(meta->func_id));
+ err = check_func_arg_reg_off(env, reg, regno, arg_type);
if (err)
return err;

skip_type_check:
- /* check_func_arg_reg_off relies on only one referenced register being
- * allowed for BPF helpers.
- */
+ if (arg_type_is_release(arg_type)) {
+ if (!reg->ref_obj_id && !register_is_null(reg)) {
+ verbose(env, "R%d must be referenced when passed to release function\n",
+ regno);
+ return -EINVAL;
+ }
+ if (meta->release_regno) {
+ verbose(env, "verifier internal error: more than one release argument\n");
+ return -EFAULT;
+ }
+ meta->release_regno = regno;
+ }
+
if (reg->ref_obj_id) {
if (meta->ref_obj_id) {
verbose(env, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n",
@@ -6151,7 +6153,8 @@ static bool check_btf_id_ok(const struct bpf_func_proto *fn)
return true;
}

-static int check_func_proto(const struct bpf_func_proto *fn, int func_id)
+static int check_func_proto(const struct bpf_func_proto *fn, int func_id,
+ struct bpf_call_arg_meta *meta)
{
return check_raw_mode_ok(fn) &&
check_arg_pair_ok(fn) &&
@@ -6833,7 +6836,7 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
memset(&meta, 0, sizeof(meta));
meta.pkt_access = fn->pkt_access;

- err = check_func_proto(fn, func_id);
+ err = check_func_proto(fn, func_id, &meta);
if (err) {
verbose(env, "kernel subsystem misconfigured func %s#%d\n",
func_id_name(func_id), func_id);
@@ -6866,8 +6869,17 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
return err;
}

- if (is_release_function(func_id)) {
- err = release_reference(env, meta.ref_obj_id);
+ regs = cur_regs(env);
+
+ if (meta.release_regno) {
+ err = -EINVAL;
+ if (meta.ref_obj_id)
+ err = release_reference(env, meta.ref_obj_id);
+ /* meta.ref_obj_id can only be 0 if register that is meant to be
+ * released is NULL, which must be > R0.
+ */
+ else if (register_is_null(&regs[meta.release_regno]))
+ err = 0;
if (err) {
verbose(env, "func %s#%d reference has not been acquired before\n",
func_id_name(func_id), func_id);
@@ -6875,8 +6887,6 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
}
}

- regs = cur_regs(env);
-
switch (func_id) {
case BPF_FUNC_tail_call:
err = check_reference_leak(env);
diff --git a/net/core/filter.c b/net/core/filter.c
index d0b0c163d3f3..5db4fae23925 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6642,7 +6642,7 @@ static const struct bpf_func_proto bpf_sk_release_proto = {
.func = bpf_sk_release,
.gpl_only = false,
.ret_type = RET_INTEGER,
- .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
+ .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON | OBJ_RELEASE,
};

BPF_CALL_5(bpf_xdp_sk_lookup_udp, struct xdp_buff *, ctx,
diff --git a/tools/testing/selftests/bpf/verifier/ref_tracking.c b/tools/testing/selftests/bpf/verifier/ref_tracking.c
index fbd682520e47..57a83d763ec1 100644
--- a/tools/testing/selftests/bpf/verifier/ref_tracking.c
+++ b/tools/testing/selftests/bpf/verifier/ref_tracking.c
@@ -796,7 +796,7 @@
},
.prog_type = BPF_PROG_TYPE_SCHED_CLS,
.result = REJECT,
- .errstr = "reference has not been acquired before",
+ .errstr = "R1 must be referenced when passed to release function",
},
{
/* !bpf_sk_fullsock(sk) is checked but !bpf_tcp_sock(sk) is not checked */
diff --git a/tools/testing/selftests/bpf/verifier/sock.c b/tools/testing/selftests/bpf/verifier/sock.c
index 86b24cad27a7..d11d0b28be41 100644
--- a/tools/testing/selftests/bpf/verifier/sock.c
+++ b/tools/testing/selftests/bpf/verifier/sock.c
@@ -417,7 +417,7 @@
},
.prog_type = BPF_PROG_TYPE_SCHED_CLS,
.result = REJECT,
- .errstr = "reference has not been acquired before",
+ .errstr = "R1 must be referenced when passed to release function",
},
{
"bpf_sk_release(bpf_sk_fullsock(skb->sk))",
@@ -436,7 +436,7 @@
},
.prog_type = BPF_PROG_TYPE_SCHED_CLS,
.result = REJECT,
- .errstr = "reference has not been acquired before",
+ .errstr = "R1 must be referenced when passed to release function",
},
{
"bpf_sk_release(bpf_tcp_sock(skb->sk))",
@@ -455,7 +455,7 @@
},
.prog_type = BPF_PROG_TYPE_SCHED_CLS,
.result = REJECT,
- .errstr = "reference has not been acquired before",
+ .errstr = "R1 must be referenced when passed to release function",
},
{
"sk_storage_get(map, skb->sk, NULL, 0): value == NULL",
--
2.35.1