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-rw-r--r--include/linux/bpf.h8
-rw-r--r--include/uapi/linux/bpf.h12
-rw-r--r--kernel/bpf/btf.c10
-rw-r--r--kernel/bpf/helpers.c24
-rw-r--r--kernel/bpf/verifier.c98
-rw-r--r--tools/include/uapi/linux/bpf.h12
6 files changed, 151 insertions, 13 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 492edd2c5713..24310837bafc 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -160,8 +160,14 @@ enum {
BPF_MAP_VALUE_OFF_MAX = 8,
};
+enum bpf_kptr_type {
+ BPF_KPTR_UNREF,
+ BPF_KPTR_REF,
+};
+
struct bpf_map_value_off_desc {
u32 offset;
+ enum bpf_kptr_type type;
struct {
struct btf *btf;
u32 btf_id;
@@ -418,6 +424,7 @@ enum bpf_arg_type {
ARG_PTR_TO_STACK, /* pointer to stack */
ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */
ARG_PTR_TO_TIMER, /* pointer to bpf_timer */
+ ARG_PTR_TO_KPTR, /* pointer to referenced kptr */
__BPF_ARG_TYPE_MAX,
/* Extended arg_types. */
@@ -427,6 +434,7 @@ enum bpf_arg_type {
ARG_PTR_TO_SOCKET_OR_NULL = PTR_MAYBE_NULL | ARG_PTR_TO_SOCKET,
ARG_PTR_TO_ALLOC_MEM_OR_NULL = PTR_MAYBE_NULL | ARG_PTR_TO_ALLOC_MEM,
ARG_PTR_TO_STACK_OR_NULL = PTR_MAYBE_NULL | ARG_PTR_TO_STACK,
+ ARG_PTR_TO_BTF_ID_OR_NULL = PTR_MAYBE_NULL | ARG_PTR_TO_BTF_ID,
/* This must be the last entry. Its purpose is to ensure the enum is
* wide enough to hold the higher bits reserved for bpf_type_flag.
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index d14b10b85e51..444fe6f1cf35 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5143,6 +5143,17 @@ union bpf_attr {
* The **hash_algo** is returned on success,
* **-EOPNOTSUP** if the hash calculation failed or **-EINVAL** if
* invalid arguments are passed.
+ *
+ * void *bpf_kptr_xchg(void *map_value, void *ptr)
+ * Description
+ * Exchange kptr at pointer *map_value* with *ptr*, and return the
+ * old value. *ptr* can be NULL, otherwise it must be a referenced
+ * pointer which will be released when this helper is called.
+ * Return
+ * The old value of kptr (which can be NULL). The returned pointer
+ * if not NULL, is a reference which must be released using its
+ * corresponding release function, or moved into a BPF map before
+ * program exit.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5339,6 +5350,7 @@ union bpf_attr {
FN(copy_from_user_task), \
FN(skb_set_tstamp), \
FN(ima_file_hash), \
+ FN(kptr_xchg), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index f0287342204f..4138c51728dd 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3177,6 +3177,7 @@ enum {
struct btf_field_info {
u32 type_id;
u32 off;
+ enum bpf_kptr_type type;
};
static int btf_find_struct(const struct btf *btf, const struct btf_type *t,
@@ -3193,6 +3194,7 @@ static int btf_find_struct(const struct btf *btf, const struct btf_type *t,
static int btf_find_kptr(const struct btf *btf, const struct btf_type *t,
u32 off, int sz, struct btf_field_info *info)
{
+ enum bpf_kptr_type type;
u32 res_id;
/* For PTR, sz is always == 8 */
@@ -3205,7 +3207,11 @@ static int btf_find_kptr(const struct btf *btf, const struct btf_type *t,
/* Reject extra tags */
if (btf_type_is_type_tag(btf_type_by_id(btf, t->type)))
return -EINVAL;
- if (strcmp("kptr", __btf_name_by_offset(btf, t->name_off)))
+ if (!strcmp("kptr", __btf_name_by_offset(btf, t->name_off)))
+ type = BPF_KPTR_UNREF;
+ else if (!strcmp("kptr_ref", __btf_name_by_offset(btf, t->name_off)))
+ type = BPF_KPTR_REF;
+ else
return -EINVAL;
/* Get the base type */
@@ -3216,6 +3222,7 @@ static int btf_find_kptr(const struct btf *btf, const struct btf_type *t,
info->type_id = res_id;
info->off = off;
+ info->type = type;
return BTF_FIELD_FOUND;
}
@@ -3420,6 +3427,7 @@ struct bpf_map_value_off *btf_parse_kptrs(const struct btf *btf,
}
tab->off[i].offset = info_arr[i].off;
+ tab->off[i].type = info_arr[i].type;
tab->off[i].kptr.btf_id = id;
tab->off[i].kptr.btf = kernel_btf;
}
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 315053ef6a75..3e709fed5306 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1374,6 +1374,28 @@ out:
kfree(t);
}
+BPF_CALL_2(bpf_kptr_xchg, void *, map_value, void *, ptr)
+{
+ unsigned long *kptr = map_value;
+
+ return xchg(kptr, (unsigned long)ptr);
+}
+
+/* Unlike other PTR_TO_BTF_ID helpers the btf_id in bpf_kptr_xchg()
+ * helper is determined dynamically by the verifier.
+ */
+#define BPF_PTR_POISON ((void *)((0xeB9FUL << 2) + POISON_POINTER_DELTA))
+
+const struct bpf_func_proto bpf_kptr_xchg_proto = {
+ .func = bpf_kptr_xchg,
+ .gpl_only = false,
+ .ret_type = RET_PTR_TO_BTF_ID_OR_NULL,
+ .ret_btf_id = BPF_PTR_POISON,
+ .arg1_type = ARG_PTR_TO_KPTR,
+ .arg2_type = ARG_PTR_TO_BTF_ID_OR_NULL | OBJ_RELEASE,
+ .arg2_btf_id = BPF_PTR_POISON,
+};
+
const struct bpf_func_proto bpf_get_current_task_proto __weak;
const struct bpf_func_proto bpf_get_current_task_btf_proto __weak;
const struct bpf_func_proto bpf_probe_read_user_proto __weak;
@@ -1452,6 +1474,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
return &bpf_timer_start_proto;
case BPF_FUNC_timer_cancel:
return &bpf_timer_cancel_proto;
+ case BPF_FUNC_kptr_xchg:
+ return &bpf_kptr_xchg_proto;
default:
break;
}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5426bab7f02c..c9ee44efed89 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -258,6 +258,7 @@ struct bpf_call_arg_meta {
struct btf *ret_btf;
u32 ret_btf_id;
u32 subprogno;
+ struct bpf_map_value_off_desc *kptr_off_desc;
};
struct btf *btf_vmlinux;
@@ -489,7 +490,8 @@ static bool is_acquire_function(enum bpf_func_id func_id,
if (func_id == BPF_FUNC_sk_lookup_tcp ||
func_id == BPF_FUNC_sk_lookup_udp ||
func_id == BPF_FUNC_skc_lookup_tcp ||
- func_id == BPF_FUNC_ringbuf_reserve)
+ func_id == BPF_FUNC_ringbuf_reserve ||
+ func_id == BPF_FUNC_kptr_xchg)
return true;
if (func_id == BPF_FUNC_map_lookup_elem &&
@@ -3514,6 +3516,12 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
/* We need to verify reg->type and reg->btf, before accessing reg->btf */
reg_name = kernel_type_name(reg->btf, reg->btf_id);
+ /* For ref_ptr case, release function check should ensure we get one
+ * referenced PTR_TO_BTF_ID, and that its fixed offset is 0. For the
+ * normal store of unreferenced kptr, we must ensure var_off is zero.
+ * Since ref_ptr cannot be accessed directly by BPF insns, checks for
+ * reg->off and reg->ref_obj_id are not needed here.
+ */
if (__check_ptr_off_reg(env, reg, regno, true))
return -EACCES;
@@ -3569,6 +3577,12 @@ static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
return -EACCES;
}
+ /* We cannot directly access kptr_ref */
+ if (off_desc->type == BPF_KPTR_REF) {
+ verbose(env, "accessing referenced kptr disallowed\n");
+ return -EACCES;
+ }
+
if (class == BPF_LDX) {
val_reg = reg_state(env, value_regno);
/* We can simply mark the value_regno receiving the pointer
@@ -5293,6 +5307,53 @@ static int process_timer_func(struct bpf_verifier_env *env, int regno,
return 0;
}
+static int process_kptr_func(struct bpf_verifier_env *env, int regno,
+ struct bpf_call_arg_meta *meta)
+{
+ struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
+ struct bpf_map_value_off_desc *off_desc;
+ struct bpf_map *map_ptr = reg->map_ptr;
+ u32 kptr_off;
+ int ret;
+
+ if (!tnum_is_const(reg->var_off)) {
+ verbose(env,
+ "R%d doesn't have constant offset. kptr has to be at the constant offset\n",
+ regno);
+ return -EINVAL;
+ }
+ if (!map_ptr->btf) {
+ verbose(env, "map '%s' has to have BTF in order to use bpf_kptr_xchg\n",
+ map_ptr->name);
+ return -EINVAL;
+ }
+ if (!map_value_has_kptrs(map_ptr)) {
+ ret = PTR_ERR(map_ptr->kptr_off_tab);
+ if (ret == -E2BIG)
+ verbose(env, "map '%s' has more than %d kptr\n", map_ptr->name,
+ BPF_MAP_VALUE_OFF_MAX);
+ else if (ret == -EEXIST)
+ verbose(env, "map '%s' has repeating kptr BTF tags\n", map_ptr->name);
+ else
+ verbose(env, "map '%s' has no valid kptr\n", map_ptr->name);
+ return -EINVAL;
+ }
+
+ meta->map_ptr = map_ptr;
+ kptr_off = reg->off + reg->var_off.value;
+ off_desc = bpf_map_kptr_off_contains(map_ptr, kptr_off);
+ if (!off_desc) {
+ verbose(env, "off=%d doesn't point to kptr\n", kptr_off);
+ return -EACCES;
+ }
+ if (off_desc->type != BPF_KPTR_REF) {
+ verbose(env, "off=%d kptr isn't referenced kptr\n", kptr_off);
+ return -EACCES;
+ }
+ meta->kptr_off_desc = off_desc;
+ return 0;
+}
+
static bool arg_type_is_mem_ptr(enum bpf_arg_type type)
{
return base_type(type) == ARG_PTR_TO_MEM ||
@@ -5433,6 +5494,7 @@ static const struct bpf_reg_types func_ptr_types = { .types = { PTR_TO_FUNC } };
static const struct bpf_reg_types stack_ptr_types = { .types = { PTR_TO_STACK } };
static const struct bpf_reg_types const_str_ptr_types = { .types = { PTR_TO_MAP_VALUE } };
static const struct bpf_reg_types timer_types = { .types = { PTR_TO_MAP_VALUE } };
+static const struct bpf_reg_types kptr_types = { .types = { PTR_TO_MAP_VALUE } };
static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
[ARG_PTR_TO_MAP_KEY] = &map_key_value_types,
@@ -5460,11 +5522,13 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
[ARG_PTR_TO_STACK] = &stack_ptr_types,
[ARG_PTR_TO_CONST_STR] = &const_str_ptr_types,
[ARG_PTR_TO_TIMER] = &timer_types,
+ [ARG_PTR_TO_KPTR] = &kptr_types,
};
static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
enum bpf_arg_type arg_type,
- const u32 *arg_btf_id)
+ const u32 *arg_btf_id,
+ struct bpf_call_arg_meta *meta)
{
struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
enum bpf_reg_type expected, type = reg->type;
@@ -5517,8 +5581,11 @@ found:
arg_btf_id = compatible->btf_id;
}
- if (!btf_struct_ids_match(&env->log, reg->btf, reg->btf_id, reg->off,
- btf_vmlinux, *arg_btf_id)) {
+ if (meta->func_id == BPF_FUNC_kptr_xchg) {
+ if (map_kptr_match_type(env, meta->kptr_off_desc, reg, regno))
+ return -EACCES;
+ } else if (!btf_struct_ids_match(&env->log, reg->btf, reg->btf_id, reg->off,
+ btf_vmlinux, *arg_btf_id)) {
verbose(env, "R%d is of type %s but %s is expected\n",
regno, kernel_type_name(reg->btf, reg->btf_id),
kernel_type_name(btf_vmlinux, *arg_btf_id));
@@ -5625,7 +5692,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
*/
goto skip_type_check;
- err = check_reg_type(env, regno, arg_type, fn->arg_btf_id[arg]);
+ err = check_reg_type(env, regno, arg_type, fn->arg_btf_id[arg], meta);
if (err)
return err;
@@ -5801,6 +5868,9 @@ skip_type_check:
verbose(env, "string is not zero-terminated\n");
return -EINVAL;
}
+ } else if (arg_type == ARG_PTR_TO_KPTR) {
+ if (process_kptr_func(env, regno, meta))
+ return -EACCES;
}
return err;
@@ -6143,10 +6213,10 @@ static bool check_btf_id_ok(const struct bpf_func_proto *fn)
int i;
for (i = 0; i < ARRAY_SIZE(fn->arg_type); i++) {
- if (fn->arg_type[i] == ARG_PTR_TO_BTF_ID && !fn->arg_btf_id[i])
+ if (base_type(fn->arg_type[i]) == ARG_PTR_TO_BTF_ID && !fn->arg_btf_id[i])
return false;
- if (fn->arg_type[i] != ARG_PTR_TO_BTF_ID && fn->arg_btf_id[i])
+ if (base_type(fn->arg_type[i]) != ARG_PTR_TO_BTF_ID && fn->arg_btf_id[i])
return false;
}
@@ -7012,21 +7082,25 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
regs[BPF_REG_0].btf_id = meta.ret_btf_id;
}
} else if (base_type(ret_type) == RET_PTR_TO_BTF_ID) {
+ struct btf *ret_btf;
int ret_btf_id;
mark_reg_known_zero(env, regs, BPF_REG_0);
regs[BPF_REG_0].type = PTR_TO_BTF_ID | ret_flag;
- ret_btf_id = *fn->ret_btf_id;
+ if (func_id == BPF_FUNC_kptr_xchg) {
+ ret_btf = meta.kptr_off_desc->kptr.btf;
+ ret_btf_id = meta.kptr_off_desc->kptr.btf_id;
+ } else {
+ ret_btf = btf_vmlinux;
+ ret_btf_id = *fn->ret_btf_id;
+ }
if (ret_btf_id == 0) {
verbose(env, "invalid return type %u of func %s#%d\n",
base_type(ret_type), func_id_name(func_id),
func_id);
return -EINVAL;
}
- /* current BPF helper definitions are only coming from
- * built-in code with type IDs from vmlinux BTF
- */
- regs[BPF_REG_0].btf = btf_vmlinux;
+ regs[BPF_REG_0].btf = ret_btf;
regs[BPF_REG_0].btf_id = ret_btf_id;
} else {
verbose(env, "unknown return type %u of func %s#%d\n",
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index d14b10b85e51..444fe6f1cf35 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5143,6 +5143,17 @@ union bpf_attr {
* The **hash_algo** is returned on success,
* **-EOPNOTSUP** if the hash calculation failed or **-EINVAL** if
* invalid arguments are passed.
+ *
+ * void *bpf_kptr_xchg(void *map_value, void *ptr)
+ * Description
+ * Exchange kptr at pointer *map_value* with *ptr*, and return the
+ * old value. *ptr* can be NULL, otherwise it must be a referenced
+ * pointer which will be released when this helper is called.
+ * Return
+ * The old value of kptr (which can be NULL). The returned pointer
+ * if not NULL, is a reference which must be released using its
+ * corresponding release function, or moved into a BPF map before
+ * program exit.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5339,6 +5350,7 @@ union bpf_attr {
FN(copy_from_user_task), \
FN(skb_set_tstamp), \
FN(ima_file_hash), \
+ FN(kptr_xchg), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.