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bpf: Add kfunc bpf_rcu_read_lock/unlock()

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Add two kfunc's bpf_rcu_read_lock() and bpf_rcu_read_unlock(). These two kfunc's
can be used for all program types. The following is an example about how
rcu pointer are used w.r.t. bpf_rcu_read_lock()/bpf_rcu_read_unlock().

  struct task_struct {
    ...
    struct task_struct              *last_wakee;
    struct task_struct __rcu        *real_parent;
    ...
  };

Let us say prog does 'task = bpf_get_current_task_btf()' to get a
'task' pointer. The basic rules are:
  - 'real_parent = task->real_parent' should be inside bpf_rcu_read_lock
    region. This is to simulate rcu_dereference() operation. The
    'real_parent' is marked as MEM_RCU only if (1). task->real_parent is
    inside bpf_rcu_read_lock region, and (2). task is a trusted ptr. So
    MEM_RCU marked ptr can be 'trusted' inside the bpf_rcu_read_lock region.
  - 'last_wakee = real_parent->last_wakee' should be inside bpf_rcu_read_lock
    region since it tries to access rcu protected memory.
  - the ptr 'last_wakee' will be marked as PTR_UNTRUSTED since in general
    it is not clear whether the object pointed by 'last_wakee' is valid or
    not even inside bpf_rcu_read_lock region.

The verifier will reset all rcu pointer register states to untrusted
at bpf_rcu_read_unlock() kfunc call site, so any such rcu pointer
won't be trusted any more outside the bpf_rcu_read_lock() region.

The current implementation does not support nested rcu read lock
region in the prog.

Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20221124053217.2373910-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yonghong Song 2022-11-23 21:32:17 -08:00 committed by Alexei Starovoitov
parent 01685c5bdd
commit 9bb00b2895
5 changed files with 155 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/bpf.h
View File

@ -572,6 +572,9 @@ enum bpf_type_flag {
*/
PTR_TRUSTED = BIT(12 + BPF_BASE_TYPE_BITS),
/* MEM is tagged with rcu and memory access needs rcu_read_lock protection. */
MEM_RCU = BIT(13 + BPF_BASE_TYPE_BITS),
__BPF_TYPE_FLAG_MAX,
__BPF_TYPE_LAST_FLAG = __BPF_TYPE_FLAG_MAX - 1,
};

5
include/linux/bpf_verifier.h
View File

@ -344,6 +344,7 @@ struct bpf_verifier_state {
u32 id;
} active_lock;
bool speculative;
bool active_rcu_lock;
/* first and last insn idx of this verifier state */
u32 first_insn_idx;
@ -445,6 +446,7 @@ struct bpf_insn_aux_data {
u32 seen; /* this insn was processed by the verifier at env->pass_cnt */
bool sanitize_stack_spill; /* subject to Spectre v4 sanitation */
bool zext_dst; /* this insn zero extends dst reg */
bool storage_get_func_atomic; /* bpf_*_storage_get() with atomic memory alloc */
u8 alu_state; /* used in combination with alu_limit */
/* below fields are initialized once */
@ -534,6 +536,7 @@ struct bpf_verifier_env {
bool bypass_spec_v1;
bool bypass_spec_v4;
bool seen_direct_write;
bool rcu_tag_supported;
struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
const struct bpf_line_info *prev_linfo;
struct bpf_verifier_log log;
@ -680,7 +683,7 @@ static inline bool bpf_prog_check_recur(const struct bpf_prog *prog)
}
}
#define BPF_REG_TRUSTED_MODIFIERS (MEM_ALLOC | PTR_TRUSTED)
#define BPF_REG_TRUSTED_MODIFIERS (MEM_ALLOC | MEM_RCU | PTR_TRUSTED)
static inline bool bpf_type_has_unsafe_modifiers(u32 type)
{

3
kernel/bpf/btf.c
View File

@ -6238,6 +6238,9 @@ error:
/* check __percpu tag */
if (strcmp(tag_value, "percpu") == 0)
tmp_flag = MEM_PERCPU;
/* check __rcu tag */
if (strcmp(tag_value, "rcu") == 0)
tmp_flag = MEM_RCU;
}
stype = btf_type_skip_modifiers(btf, mtype->type, &id);

12
kernel/bpf/helpers.c
View File

@ -1990,6 +1990,16 @@ void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k)
return obj__ign;
}
void bpf_rcu_read_lock(void)
{
rcu_read_lock();
}
void bpf_rcu_read_unlock(void)
{
rcu_read_unlock();
}
__diag_pop();
BTF_SET8_START(generic_btf_ids)
@ -2031,6 +2041,8 @@ BTF_ID(func, bpf_cgroup_release)
BTF_SET8_START(common_btf_ids)
BTF_ID_FLAGS(func, bpf_cast_to_kern_ctx)
BTF_ID_FLAGS(func, bpf_rdonly_cast)
BTF_ID_FLAGS(func, bpf_rcu_read_lock)
BTF_ID_FLAGS(func, bpf_rcu_read_unlock)
BTF_SET8_END(common_btf_ids)
static const struct btf_kfunc_id_set common_kfunc_set = {

162
kernel/bpf/verifier.c
View File

@ -527,6 +527,14 @@ static bool is_callback_calling_function(enum bpf_func_id func_id)
func_id == BPF_FUNC_user_ringbuf_drain;
}
static bool is_storage_get_function(enum bpf_func_id func_id)
{
return func_id == BPF_FUNC_sk_storage_get ||
func_id == BPF_FUNC_inode_storage_get ||
func_id == BPF_FUNC_task_storage_get ||
func_id == BPF_FUNC_cgrp_storage_get;
}
static bool helper_multiple_ref_obj_use(enum bpf_func_id func_id,
const struct bpf_map *map)
{
@ -589,11 +597,12 @@ static const char *reg_type_str(struct bpf_verifier_env *env,
strncpy(postfix, "_or_null", 16);
}
snprintf(prefix, sizeof(prefix), "%s%s%s%s%s%s",
snprintf(prefix, sizeof(prefix), "%s%s%s%s%s%s%s",
type & MEM_RDONLY ? "rdonly_" : "",
type & MEM_RINGBUF ? "ringbuf_" : "",
type & MEM_USER ? "user_" : "",
type & MEM_PERCPU ? "percpu_" : "",
type & MEM_RCU ? "rcu_" : "",
type & PTR_UNTRUSTED ? "untrusted_" : "",
type & PTR_TRUSTED ? "trusted_" : ""
);
@ -1220,6 +1229,7 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
dst_state->frame[i] = NULL;
}
dst_state->speculative = src->speculative;
dst_state->active_rcu_lock = src->active_rcu_lock;
dst_state->curframe = src->curframe;
dst_state->active_lock.ptr = src->active_lock.ptr;
dst_state->active_lock.id = src->active_lock.id;
@ -4258,6 +4268,25 @@ static bool is_flow_key_reg(struct bpf_verifier_env *env, int regno)
return reg->type == PTR_TO_FLOW_KEYS;
}
static bool is_trusted_reg(const struct bpf_reg_state *reg)
{
/* A referenced register is always trusted. */
if (reg->ref_obj_id)
return true;
/* If a register is not referenced, it is trusted if it has the
* MEM_ALLOC, MEM_RCU or PTR_TRUSTED type modifiers, and no others. Some of the
* other type modifiers may be safe, but we elect to take an opt-in
* approach here as some (e.g. PTR_UNTRUSTED and PTR_MAYBE_NULL) are
* not.
*
* Eventually, we should make PTR_TRUSTED the single source of truth
* for whether a register is trusted.
*/
return type_flag(reg->type) & BPF_REG_TRUSTED_MODIFIERS &&
!bpf_type_has_unsafe_modifiers(reg->type);
}
static int check_pkt_ptr_alignment(struct bpf_verifier_env *env,
const struct bpf_reg_state *reg,
int off, int size, bool strict)
@ -4737,9 +4766,28 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
if (type_flag(reg->type) & PTR_UNTRUSTED)
flag |= PTR_UNTRUSTED;
/* Any pointer obtained from walking a trusted pointer is no longer trusted. */
/* By default any pointer obtained from walking a trusted pointer is
* no longer trusted except the rcu case below.
*/
flag &= ~PTR_TRUSTED;
if (flag & MEM_RCU) {
/* Mark value register as MEM_RCU only if it is protected by
* bpf_rcu_read_lock() and the ptr reg is trusted. MEM_RCU
* itself can already indicate trustedness inside the rcu
* read lock region. Also mark it as PTR_TRUSTED.
*/
if (!env->cur_state->active_rcu_lock || !is_trusted_reg(reg))
flag &= ~MEM_RCU;
else
flag |= PTR_TRUSTED;
} else if (reg->type & MEM_RCU) {
/* ptr (reg) is marked as MEM_RCU, but the struct field is not tagged
* with __rcu. Mark the flag as PTR_UNTRUSTED conservatively.
*/
flag |= PTR_UNTRUSTED;
}
if (atype == BPF_READ && value_regno >= 0)
mark_btf_ld_reg(env, regs, value_regno, ret, reg->btf, btf_id, flag);
@ -5897,6 +5945,7 @@ static const struct bpf_reg_types btf_ptr_types = {
.types = {
PTR_TO_BTF_ID,
PTR_TO_BTF_ID | PTR_TRUSTED,
PTR_TO_BTF_ID | MEM_RCU | PTR_TRUSTED,
},
};
static const struct bpf_reg_types percpu_btf_ptr_types = {
@ -6075,6 +6124,7 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env,
case PTR_TO_BTF_ID:
case PTR_TO_BTF_ID | MEM_ALLOC:
case PTR_TO_BTF_ID | PTR_TRUSTED:
case PTR_TO_BTF_ID | MEM_RCU | PTR_TRUSTED:
case PTR_TO_BTF_ID | MEM_ALLOC | PTR_TRUSTED:
/* When referenced PTR_TO_BTF_ID is passed to release function,
* it's fixed offset must be 0. In the other cases, fixed offset
@ -7539,6 +7589,17 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
return err;
}
if (env->cur_state->active_rcu_lock) {
if (fn->might_sleep) {
verbose(env, "sleepable helper %s#%d in rcu_read_lock region\n",
func_id_name(func_id), func_id);
return -EINVAL;
}
if (env->prog->aux->sleepable && is_storage_get_function(func_id))
env->insn_aux_data[insn_idx].storage_get_func_atomic = true;
}
meta.func_id = func_id;
/* check args */
for (i = 0; i < MAX_BPF_FUNC_REG_ARGS; i++) {
@ -7966,25 +8027,6 @@ static bool is_kfunc_arg_kptr_get(struct bpf_kfunc_call_arg_meta *meta, int arg)
return arg == 0 && (meta->kfunc_flags & KF_KPTR_GET);
}
static bool is_trusted_reg(const struct bpf_reg_state *reg)
{
/* A referenced register is always trusted. */
if (reg->ref_obj_id)
return true;
/* If a register is not referenced, it is trusted if it has either the
* MEM_ALLOC or PTR_TRUSTED type modifiers, and no others. Some of the
* other type modifiers may be safe, but we elect to take an opt-in
* approach here as some (e.g. PTR_UNTRUSTED and PTR_MAYBE_NULL) are
* not.
*
* Eventually, we should make PTR_TRUSTED the single source of truth
* for whether a register is trusted.
*/
return type_flag(reg->type) & BPF_REG_TRUSTED_MODIFIERS &&
!bpf_type_has_unsafe_modifiers(reg->type);
}
static bool __kfunc_param_match_suffix(const struct btf *btf,
const struct btf_param *arg,
const char *suffix)
@ -8163,6 +8205,8 @@ enum special_kfunc_type {
KF_bpf_list_pop_back,
KF_bpf_cast_to_kern_ctx,
KF_bpf_rdonly_cast,
KF_bpf_rcu_read_lock,
KF_bpf_rcu_read_unlock,
};
BTF_SET_START(special_kfunc_set)
@ -8185,6 +8229,18 @@ BTF_ID(func, bpf_list_pop_front)
BTF_ID(func, bpf_list_pop_back)
BTF_ID(func, bpf_cast_to_kern_ctx)
BTF_ID(func, bpf_rdonly_cast)
BTF_ID(func, bpf_rcu_read_lock)
BTF_ID(func, bpf_rcu_read_unlock)
static bool is_kfunc_bpf_rcu_read_lock(struct bpf_kfunc_call_arg_meta *meta)
{
return meta->func_id == special_kfunc_list[KF_bpf_rcu_read_lock];
}
static bool is_kfunc_bpf_rcu_read_unlock(struct bpf_kfunc_call_arg_meta *meta)
{
return meta->func_id == special_kfunc_list[KF_bpf_rcu_read_unlock];
}
static enum kfunc_ptr_arg_type
get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
@ -8817,6 +8873,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
const struct btf_type *t, *func, *func_proto, *ptr_type;
struct bpf_reg_state *regs = cur_regs(env);
const char *func_name, *ptr_type_name;
bool sleepable, rcu_lock, rcu_unlock;
struct bpf_kfunc_call_arg_meta meta;
u32 i, nargs, func_id, ptr_type_id;
int err, insn_idx = *insn_idx_p;
@ -8858,11 +8915,45 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
return -EACCES;
}
if (is_kfunc_sleepable(&meta) && !env->prog->aux->sleepable) {
sleepable = is_kfunc_sleepable(&meta);
if (sleepable && !env->prog->aux->sleepable) {
verbose(env, "program must be sleepable to call sleepable kfunc %s\n", func_name);
return -EACCES;
}
rcu_lock = is_kfunc_bpf_rcu_read_lock(&meta);
rcu_unlock = is_kfunc_bpf_rcu_read_unlock(&meta);
if ((rcu_lock || rcu_unlock) && !env->rcu_tag_supported) {
verbose(env, "no vmlinux btf rcu tag support for kfunc %s\n", func_name);
return -EACCES;
}
if (env->cur_state->active_rcu_lock) {
struct bpf_func_state *state;
struct bpf_reg_state *reg;
if (rcu_lock) {
verbose(env, "nested rcu read lock (kernel function %s)\n", func_name);
return -EINVAL;
} else if (rcu_unlock) {
bpf_for_each_reg_in_vstate(env->cur_state, state, reg, ({
if (reg->type & MEM_RCU) {
reg->type &= ~(MEM_RCU | PTR_TRUSTED);
reg->type |= PTR_UNTRUSTED;
}
}));
env->cur_state->active_rcu_lock = false;
} else if (sleepable) {
verbose(env, "kernel func %s is sleepable within rcu_read_lock region\n", func_name);
return -EACCES;
}
} else if (rcu_lock) {
env->cur_state->active_rcu_lock = true;
} else if (rcu_unlock) {
verbose(env, "unmatched rcu read unlock (kernel function %s)\n", func_name);
return -EINVAL;
}
/* Check the arguments */
err = check_kfunc_args(env, &meta);
if (err < 0)
@ -11754,6 +11845,11 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
return -EINVAL;
}
if (env->cur_state->active_rcu_lock) {
verbose(env, "BPF_LD_[ABS|IND] cannot be used inside bpf_rcu_read_lock-ed region\n");
return -EINVAL;
}
if (regs[ctx_reg].type != PTR_TO_CTX) {
verbose(env,
"at the time of BPF_LD_ABS|IND R6 != pointer to skb\n");
@ -13019,6 +13115,9 @@ static bool states_equal(struct bpf_verifier_env *env,
old->active_lock.id != cur->active_lock.id)
return false;
if (old->active_rcu_lock != cur->active_rcu_lock)
return false;
/* for states to be equal callsites have to be the same
* and all frame states need to be equivalent
*/
@ -13706,6 +13805,11 @@ static int do_check(struct bpf_verifier_env *env)
return -EINVAL;
}
if (env->cur_state->active_rcu_lock) {
verbose(env, "bpf_rcu_read_unlock is missing\n");
return -EINVAL;
}
/* We must do check_reference_leak here before
* prepare_func_exit to handle the case when
* state->curframe > 0, it may be a callback
@ -15494,14 +15598,12 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
goto patch_call_imm;
}
if (insn->imm == BPF_FUNC_task_storage_get ||
insn->imm == BPF_FUNC_sk_storage_get ||
insn->imm == BPF_FUNC_inode_storage_get ||
insn->imm == BPF_FUNC_cgrp_storage_get) {
if (env->prog->aux->sleepable)
insn_buf[0] = BPF_MOV64_IMM(BPF_REG_5, (__force __s32)GFP_KERNEL);
else
if (is_storage_get_function(insn->imm)) {
if (!env->prog->aux->sleepable ||
env->insn_aux_data[i + delta].storage_get_func_atomic)
insn_buf[0] = BPF_MOV64_IMM(BPF_REG_5, (__force __s32)GFP_ATOMIC);
else
insn_buf[0] = BPF_MOV64_IMM(BPF_REG_5, (__force __s32)GFP_KERNEL);
insn_buf[1] = *insn;
cnt = 2;
@ -16580,6 +16682,8 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr)
env->bypass_spec_v1 = bpf_bypass_spec_v1();
env->bypass_spec_v4 = bpf_bypass_spec_v4();
env->bpf_capable = bpf_capable();
env->rcu_tag_supported = btf_vmlinux &&
btf_find_by_name_kind(btf_vmlinux, "rcu", BTF_KIND_TYPE_TAG) > 0;
if (is_priv)
env->test_state_freq = attr->prog_flags & BPF_F_TEST_STATE_FREQ;