* [PATCH bpf-next v6 1/2] bpf: Refactor active lock management
2024-11-09 23:14 [PATCH bpf-next v6 0/2] Refactor lock management Kumar Kartikeya Dwivedi
@ 2024-11-09 23:14 ` Kumar Kartikeya Dwivedi
2024-11-09 23:14 ` [PATCH bpf-next v6 2/2] bpf: Drop special callback reference handling Kumar Kartikeya Dwivedi
2024-11-10 0:10 ` [PATCH bpf-next v6 0/2] Refactor lock management patchwork-bot+netdevbpf
2 siblings, 0 replies; 4+ messages in thread
From: Kumar Kartikeya Dwivedi @ 2024-11-09 23:14 UTC (permalink / raw)
To: bpf
Cc: kkd, Alexei Starovoitov, Andrii Nakryiko, Daniel Borkmann,
Martin KaFai Lau, Eduard Zingerman, kernel-team
When bpf_spin_lock was introduced originally, there was deliberation on
whether to use an array of lock IDs, but since bpf_spin_lock is limited
to holding a single lock at any given time, we've been using a single ID
to identify the held lock.
In preparation for introducing spin locks that can be taken multiple
times, introduce support for acquiring multiple lock IDs. For this
purpose, reuse the acquired_refs array and store both lock and pointer
references. We tag the entry with REF_TYPE_PTR or REF_TYPE_LOCK to
disambiguate and find the relevant entry. The ptr field is used to track
the map_ptr or btf (for bpf_obj_new allocations) to ensure locks can be
matched with protected fields within the same "allocation", i.e.
bpf_obj_new object or map value.
The struct active_lock is changed to an int as the state is part of the
acquired_refs array, and we only need active_lock as a cheap way of
detecting lock presence.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
include/linux/bpf_verifier.h | 53 ++++++-------
kernel/bpf/verifier.c | 146 +++++++++++++++++++++++++----------
2 files changed, 132 insertions(+), 67 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 4513372c5bc8..d84beed92ae4 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -48,22 +48,6 @@ enum bpf_reg_liveness {
REG_LIVE_DONE = 0x8, /* liveness won't be updating this register anymore */
};
-/* For every reg representing a map value or allocated object pointer,
- * we consider the tuple of (ptr, id) for them to be unique in verifier
- * context and conside them to not alias each other for the purposes of
- * tracking lock state.
- */
-struct bpf_active_lock {
- /* This can either be reg->map_ptr or reg->btf. If ptr is NULL,
- * there's no active lock held, and other fields have no
- * meaning. If non-NULL, it indicates that a lock is held and
- * id member has the reg->id of the register which can be >= 0.
- */
- void *ptr;
- /* This will be reg->id */
- u32 id;
-};
-
#define ITER_PREFIX "bpf_iter_"
enum bpf_iter_state {
@@ -266,6 +250,13 @@ struct bpf_stack_state {
};
struct bpf_reference_state {
+ /* Each reference object has a type. Ensure REF_TYPE_PTR is zero to
+ * default to pointer reference on zero initialization of a state.
+ */
+ enum ref_state_type {
+ REF_TYPE_PTR = 0,
+ REF_TYPE_LOCK,
+ } type;
/* Track each reference created with a unique id, even if the same
* instruction creates the reference multiple times (eg, via CALL).
*/
@@ -274,17 +265,23 @@ struct bpf_reference_state {
* is used purely to inform the user of a reference leak.
*/
int insn_idx;
- /* There can be a case like:
- * main (frame 0)
- * cb (frame 1)
- * func (frame 3)
- * cb (frame 4)
- * Hence for frame 4, if callback_ref just stored boolean, it would be
- * impossible to distinguish nested callback refs. Hence store the
- * frameno and compare that to callback_ref in check_reference_leak when
- * exiting a callback function.
- */
- int callback_ref;
+ union {
+ /* There can be a case like:
+ * main (frame 0)
+ * cb (frame 1)
+ * func (frame 3)
+ * cb (frame 4)
+ * Hence for frame 4, if callback_ref just stored boolean, it would be
+ * impossible to distinguish nested callback refs. Hence store the
+ * frameno and compare that to callback_ref in check_reference_leak when
+ * exiting a callback function.
+ */
+ int callback_ref;
+ /* Use to keep track of the source object of a lock, to ensure
+ * it matches on unlock.
+ */
+ void *ptr;
+ };
};
struct bpf_retval_range {
@@ -332,6 +329,7 @@ struct bpf_func_state {
/* The following fields should be last. See copy_func_state() */
int acquired_refs;
+ int active_locks;
struct bpf_reference_state *refs;
/* The state of the stack. Each element of the array describes BPF_REG_SIZE
* (i.e. 8) bytes worth of stack memory.
@@ -434,7 +432,6 @@ struct bpf_verifier_state {
u32 insn_idx;
u32 curframe;
- struct bpf_active_lock active_lock;
bool speculative;
bool active_rcu_lock;
u32 active_preempt_lock;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 132fc172961f..d55ca27dc031 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1284,6 +1284,7 @@ static int copy_reference_state(struct bpf_func_state *dst, const struct bpf_fun
if (!dst->refs)
return -ENOMEM;
+ dst->active_locks = src->active_locks;
dst->acquired_refs = src->acquired_refs;
return 0;
}
@@ -1354,6 +1355,7 @@ static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx)
if (err)
return err;
id = ++env->id_gen;
+ state->refs[new_ofs].type = REF_TYPE_PTR;
state->refs[new_ofs].id = id;
state->refs[new_ofs].insn_idx = insn_idx;
state->refs[new_ofs].callback_ref = state->in_callback_fn ? state->frameno : 0;
@@ -1361,6 +1363,25 @@ static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx)
return id;
}
+static int acquire_lock_state(struct bpf_verifier_env *env, int insn_idx, enum ref_state_type type,
+ int id, void *ptr)
+{
+ struct bpf_func_state *state = cur_func(env);
+ int new_ofs = state->acquired_refs;
+ int err;
+
+ err = resize_reference_state(state, state->acquired_refs + 1);
+ if (err)
+ return err;
+ state->refs[new_ofs].type = type;
+ state->refs[new_ofs].id = id;
+ state->refs[new_ofs].insn_idx = insn_idx;
+ state->refs[new_ofs].ptr = ptr;
+
+ state->active_locks++;
+ return 0;
+}
+
/* release function corresponding to acquire_reference_state(). Idempotent. */
static int release_reference_state(struct bpf_func_state *state, int ptr_id)
{
@@ -1368,6 +1389,8 @@ static int release_reference_state(struct bpf_func_state *state, int ptr_id)
last_idx = state->acquired_refs - 1;
for (i = 0; i < state->acquired_refs; i++) {
+ if (state->refs[i].type != REF_TYPE_PTR)
+ continue;
if (state->refs[i].id == ptr_id) {
/* Cannot release caller references in callbacks */
if (state->in_callback_fn && state->refs[i].callback_ref != state->frameno)
@@ -1383,6 +1406,45 @@ static int release_reference_state(struct bpf_func_state *state, int ptr_id)
return -EINVAL;
}
+static int release_lock_state(struct bpf_func_state *state, int type, int id, void *ptr)
+{
+ int i, last_idx;
+
+ last_idx = state->acquired_refs - 1;
+ for (i = 0; i < state->acquired_refs; i++) {
+ if (state->refs[i].type != type)
+ continue;
+ if (state->refs[i].id == id && state->refs[i].ptr == ptr) {
+ if (last_idx && i != last_idx)
+ memcpy(&state->refs[i], &state->refs[last_idx],
+ sizeof(*state->refs));
+ memset(&state->refs[last_idx], 0, sizeof(*state->refs));
+ state->acquired_refs--;
+ state->active_locks--;
+ return 0;
+ }
+ }
+ return -EINVAL;
+}
+
+static struct bpf_reference_state *find_lock_state(struct bpf_verifier_env *env, enum ref_state_type type,
+ int id, void *ptr)
+{
+ struct bpf_func_state *state = cur_func(env);
+ int i;
+
+ for (i = 0; i < state->acquired_refs; i++) {
+ struct bpf_reference_state *s = &state->refs[i];
+
+ if (s->type == REF_TYPE_PTR || s->type != type)
+ continue;
+
+ if (s->id == id && s->ptr == ptr)
+ return s;
+ }
+ return NULL;
+}
+
static void free_func_state(struct bpf_func_state *state)
{
if (!state)
@@ -1453,8 +1515,6 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
dst_state->active_preempt_lock = src->active_preempt_lock;
dst_state->in_sleepable = src->in_sleepable;
dst_state->curframe = src->curframe;
- dst_state->active_lock.ptr = src->active_lock.ptr;
- dst_state->active_lock.id = src->active_lock.id;
dst_state->branches = src->branches;
dst_state->parent = src->parent;
dst_state->first_insn_idx = src->first_insn_idx;
@@ -5442,7 +5502,7 @@ static bool in_sleepable(struct bpf_verifier_env *env)
static bool in_rcu_cs(struct bpf_verifier_env *env)
{
return env->cur_state->active_rcu_lock ||
- env->cur_state->active_lock.ptr ||
+ cur_func(env)->active_locks ||
!in_sleepable(env);
}
@@ -7724,19 +7784,20 @@ static int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg
* Since only one bpf_spin_lock is allowed the checks are simpler than
* reg_is_refcounted() logic. The verifier needs to remember only
* one spin_lock instead of array of acquired_refs.
- * cur_state->active_lock remembers which map value element or allocated
+ * cur_func(env)->active_locks remembers which map value element or allocated
* object got locked and clears it after bpf_spin_unlock.
*/
static int process_spin_lock(struct bpf_verifier_env *env, int regno,
bool is_lock)
{
struct bpf_reg_state *regs = cur_regs(env), *reg = ®s[regno];
- struct bpf_verifier_state *cur = env->cur_state;
bool is_const = tnum_is_const(reg->var_off);
+ struct bpf_func_state *cur = cur_func(env);
u64 val = reg->var_off.value;
struct bpf_map *map = NULL;
struct btf *btf = NULL;
struct btf_record *rec;
+ int err;
if (!is_const) {
verbose(env,
@@ -7768,16 +7829,23 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
return -EINVAL;
}
if (is_lock) {
- if (cur->active_lock.ptr) {
+ void *ptr;
+
+ if (map)
+ ptr = map;
+ else
+ ptr = btf;
+
+ if (cur->active_locks) {
verbose(env,
"Locking two bpf_spin_locks are not allowed\n");
return -EINVAL;
}
- if (map)
- cur->active_lock.ptr = map;
- else
- cur->active_lock.ptr = btf;
- cur->active_lock.id = reg->id;
+ err = acquire_lock_state(env, env->insn_idx, REF_TYPE_LOCK, reg->id, ptr);
+ if (err < 0) {
+ verbose(env, "Failed to acquire lock state\n");
+ return err;
+ }
} else {
void *ptr;
@@ -7786,20 +7854,17 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
else
ptr = btf;
- if (!cur->active_lock.ptr) {
+ if (!cur->active_locks) {
verbose(env, "bpf_spin_unlock without taking a lock\n");
return -EINVAL;
}
- if (cur->active_lock.ptr != ptr ||
- cur->active_lock.id != reg->id) {
+
+ if (release_lock_state(cur_func(env), REF_TYPE_LOCK, reg->id, ptr)) {
verbose(env, "bpf_spin_unlock of different lock\n");
return -EINVAL;
}
invalidate_non_owning_refs(env);
-
- cur->active_lock.ptr = NULL;
- cur->active_lock.id = 0;
}
return 0;
}
@@ -9861,7 +9926,7 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
const char *sub_name = subprog_name(env, subprog);
/* Only global subprogs cannot be called with a lock held. */
- if (env->cur_state->active_lock.ptr) {
+ if (cur_func(env)->active_locks) {
verbose(env, "global function calls are not allowed while holding a lock,\n"
"use static function instead\n");
return -EINVAL;
@@ -10386,6 +10451,8 @@ static int check_reference_leak(struct bpf_verifier_env *env, bool exception_exi
return 0;
for (i = 0; i < state->acquired_refs; i++) {
+ if (state->refs[i].type != REF_TYPE_PTR)
+ continue;
if (!exception_exit && state->in_callback_fn && state->refs[i].callback_ref != state->frameno)
continue;
verbose(env, "Unreleased reference id=%d alloc_insn=%d\n",
@@ -10399,7 +10466,7 @@ static int check_resource_leak(struct bpf_verifier_env *env, bool exception_exit
{
int err;
- if (check_lock && env->cur_state->active_lock.ptr) {
+ if (check_lock && cur_func(env)->active_locks) {
verbose(env, "%s cannot be used inside bpf_spin_lock-ed region\n", prefix);
return -EINVAL;
}
@@ -11620,10 +11687,9 @@ static int process_kf_arg_ptr_to_btf_id(struct bpf_verifier_env *env,
static int ref_set_non_owning(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
{
- struct bpf_verifier_state *state = env->cur_state;
struct btf_record *rec = reg_btf_record(reg);
- if (!state->active_lock.ptr) {
+ if (!cur_func(env)->active_locks) {
verbose(env, "verifier internal error: ref_set_non_owning w/o active lock\n");
return -EFAULT;
}
@@ -11720,6 +11786,7 @@ static int ref_convert_owning_non_owning(struct bpf_verifier_env *env, u32 ref_o
*/
static int check_reg_allocation_locked(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
{
+ struct bpf_reference_state *s;
void *ptr;
u32 id;
@@ -11736,10 +11803,10 @@ static int check_reg_allocation_locked(struct bpf_verifier_env *env, struct bpf_
}
id = reg->id;
- if (!env->cur_state->active_lock.ptr)
+ if (!cur_func(env)->active_locks)
return -EINVAL;
- if (env->cur_state->active_lock.ptr != ptr ||
- env->cur_state->active_lock.id != id) {
+ s = find_lock_state(env, REF_TYPE_LOCK, id, ptr);
+ if (!s) {
verbose(env, "held lock and object are not in the same allocation\n");
return -EINVAL;
}
@@ -17635,8 +17702,22 @@ static bool refsafe(struct bpf_func_state *old, struct bpf_func_state *cur,
return false;
for (i = 0; i < old->acquired_refs; i++) {
- if (!check_ids(old->refs[i].id, cur->refs[i].id, idmap))
+ if (!check_ids(old->refs[i].id, cur->refs[i].id, idmap) ||
+ old->refs[i].type != cur->refs[i].type)
+ return false;
+ switch (old->refs[i].type) {
+ case REF_TYPE_PTR:
+ if (old->refs[i].callback_ref != cur->refs[i].callback_ref)
+ return false;
+ break;
+ case REF_TYPE_LOCK:
+ if (old->refs[i].ptr != cur->refs[i].ptr)
+ return false;
+ break;
+ default:
+ WARN_ONCE(1, "Unhandled enum type for reference state: %d\n", old->refs[i].type);
return false;
+ }
}
return true;
@@ -17714,19 +17795,6 @@ static bool states_equal(struct bpf_verifier_env *env,
if (old->speculative && !cur->speculative)
return false;
- if (old->active_lock.ptr != cur->active_lock.ptr)
- return false;
-
- /* Old and cur active_lock's have to be either both present
- * or both absent.
- */
- if (!!old->active_lock.id != !!cur->active_lock.id)
- return false;
-
- if (old->active_lock.id &&
- !check_ids(old->active_lock.id, cur->active_lock.id, &env->idmap_scratch))
- return false;
-
if (old->active_rcu_lock != cur->active_rcu_lock)
return false;
@@ -18625,7 +18693,7 @@ static int do_check(struct bpf_verifier_env *env)
return -EINVAL;
}
- if (env->cur_state->active_lock.ptr) {
+ if (cur_func(env)->active_locks) {
if ((insn->src_reg == BPF_REG_0 && insn->imm != BPF_FUNC_spin_unlock) ||
(insn->src_reg == BPF_PSEUDO_KFUNC_CALL &&
(insn->off != 0 || !is_bpf_graph_api_kfunc(insn->imm)))) {
--
2.43.5
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH bpf-next v6 2/2] bpf: Drop special callback reference handling
2024-11-09 23:14 [PATCH bpf-next v6 0/2] Refactor lock management Kumar Kartikeya Dwivedi
2024-11-09 23:14 ` [PATCH bpf-next v6 1/2] bpf: Refactor active " Kumar Kartikeya Dwivedi
@ 2024-11-09 23:14 ` Kumar Kartikeya Dwivedi
2024-11-10 0:10 ` [PATCH bpf-next v6 0/2] Refactor lock management patchwork-bot+netdevbpf
2 siblings, 0 replies; 4+ messages in thread
From: Kumar Kartikeya Dwivedi @ 2024-11-09 23:14 UTC (permalink / raw)
To: bpf
Cc: kkd, Eduard Zingerman, Alexei Starovoitov, Andrii Nakryiko,
Daniel Borkmann, Martin KaFai Lau, kernel-team
Logic to prevent callbacks from acquiring new references for the program
(i.e. leaving acquired references), and releasing caller references
(i.e. those acquired in parent frames) was introduced in commit
9d9d00ac29d0 ("bpf: Fix reference state management for synchronous callbacks").
This was necessary because back then, the verifier simulated each
callback once (that could potentially be executed N times, where N can
be zero). This meant that callbacks that left lingering resources or
cleared caller resources could do it more than once, operating on
undefined state or leaking memory.
With the fixes to callback verification in commit
ab5cfac139ab ("bpf: verify callbacks as if they are called unknown number of times"),
all of this extra logic is no longer necessary. Hence, drop it as part
of this commit.
Cc: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
include/linux/bpf_verifier.h | 21 +++-------------
kernel/bpf/verifier.c | 25 ++++---------------
.../selftests/bpf/prog_tests/cb_refs.c | 4 +--
3 files changed, 11 insertions(+), 39 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index d84beed92ae4..3a74033d49c4 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -265,23 +265,10 @@ struct bpf_reference_state {
* is used purely to inform the user of a reference leak.
*/
int insn_idx;
- union {
- /* There can be a case like:
- * main (frame 0)
- * cb (frame 1)
- * func (frame 3)
- * cb (frame 4)
- * Hence for frame 4, if callback_ref just stored boolean, it would be
- * impossible to distinguish nested callback refs. Hence store the
- * frameno and compare that to callback_ref in check_reference_leak when
- * exiting a callback function.
- */
- int callback_ref;
- /* Use to keep track of the source object of a lock, to ensure
- * it matches on unlock.
- */
- void *ptr;
- };
+ /* Use to keep track of the source object of a lock, to ensure
+ * it matches on unlock.
+ */
+ void *ptr;
};
struct bpf_retval_range {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d55ca27dc031..9f5de8d4fbd0 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1358,7 +1358,6 @@ static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx)
state->refs[new_ofs].type = REF_TYPE_PTR;
state->refs[new_ofs].id = id;
state->refs[new_ofs].insn_idx = insn_idx;
- state->refs[new_ofs].callback_ref = state->in_callback_fn ? state->frameno : 0;
return id;
}
@@ -1392,9 +1391,6 @@ static int release_reference_state(struct bpf_func_state *state, int ptr_id)
if (state->refs[i].type != REF_TYPE_PTR)
continue;
if (state->refs[i].id == ptr_id) {
- /* Cannot release caller references in callbacks */
- if (state->in_callback_fn && state->refs[i].callback_ref != state->frameno)
- return -EINVAL;
if (last_idx && i != last_idx)
memcpy(&state->refs[i], &state->refs[last_idx],
sizeof(*state->refs));
@@ -10267,17 +10263,10 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
caller->regs[BPF_REG_0] = *r0;
}
- /* callback_fn frame should have released its own additions to parent's
- * reference state at this point, or check_reference_leak would
- * complain, hence it must be the same as the caller. There is no need
- * to copy it back.
- */
- if (!callee->in_callback_fn) {
- /* Transfer references to the caller */
- err = copy_reference_state(caller, callee);
- if (err)
- return err;
- }
+ /* Transfer references to the caller */
+ err = copy_reference_state(caller, callee);
+ if (err)
+ return err;
/* for callbacks like bpf_loop or bpf_for_each_map_elem go back to callsite,
* there function call logic would reschedule callback visit. If iteration
@@ -10447,14 +10436,12 @@ static int check_reference_leak(struct bpf_verifier_env *env, bool exception_exi
bool refs_lingering = false;
int i;
- if (!exception_exit && state->frameno && !state->in_callback_fn)
+ if (!exception_exit && state->frameno)
return 0;
for (i = 0; i < state->acquired_refs; i++) {
if (state->refs[i].type != REF_TYPE_PTR)
continue;
- if (!exception_exit && state->in_callback_fn && state->refs[i].callback_ref != state->frameno)
- continue;
verbose(env, "Unreleased reference id=%d alloc_insn=%d\n",
state->refs[i].id, state->refs[i].insn_idx);
refs_lingering = true;
@@ -17707,8 +17694,6 @@ static bool refsafe(struct bpf_func_state *old, struct bpf_func_state *cur,
return false;
switch (old->refs[i].type) {
case REF_TYPE_PTR:
- if (old->refs[i].callback_ref != cur->refs[i].callback_ref)
- return false;
break;
case REF_TYPE_LOCK:
if (old->refs[i].ptr != cur->refs[i].ptr)
diff --git a/tools/testing/selftests/bpf/prog_tests/cb_refs.c b/tools/testing/selftests/bpf/prog_tests/cb_refs.c
index 3bff680de16c..c40df623a8f7 100644
--- a/tools/testing/selftests/bpf/prog_tests/cb_refs.c
+++ b/tools/testing/selftests/bpf/prog_tests/cb_refs.c
@@ -11,8 +11,8 @@ struct {
const char *prog_name;
const char *err_msg;
} cb_refs_tests[] = {
- { "underflow_prog", "reference has not been acquired before" },
- { "leak_prog", "Unreleased reference" },
+ { "underflow_prog", "must point to scalar, or struct with scalar" },
+ { "leak_prog", "Possibly NULL pointer passed to helper arg2" },
{ "nested_cb", "Unreleased reference id=4 alloc_insn=2" }, /* alloc_insn=2{4,5} */
{ "non_cb_transfer_ref", "Unreleased reference id=4 alloc_insn=1" }, /* alloc_insn=1{1,2} */
};
--
2.43.5
^ permalink raw reply related [flat|nested] 4+ messages in thread