Merge branch 'bpf: Avoid unnecessary deadlock detection and failure in task storage'

Martin KaFai Lau says:

====================

From: Martin KaFai Lau <[email protected]>

The commit bc235cd ("bpf: Prevent deadlock from recursive bpf_task_storage_[get|delete]")
added deadlock detection to avoid a tracing program from recurring
on the bpf_task_storage_{get,delete}() helpers.  These helpers acquire
a spin lock and it will lead to deadlock.

It is unnecessary for the bpf_lsm and bpf_iter programs which do
not recur.  The situation is the same as the existing
bpf_pid_task_storage_{lookup,delete}_elem() which are
used in the syscall and they also do not have deadlock detection.

This set is to add new bpf_task_storage_{get,delete}() helper proto
without the deadlock detection.  The set also removes the prog->active
check from the bpf_lsm and bpf_iter program.  Please see the individual
patch for details.
====================

Signed-off-by: Alexei Starovoitov <[email protected]>

Author: Alexei Starovoitov

arch/arm64/net/bpf_jit_comp.c

@@ -1649,13 +1649,8 @@ static void invoke_bpf_prog(struct jit_ctx *ctx, struct bpf_tramp_link *l,
 	struct bpf_prog *p = l->link.prog;
 	int cookie_off = offsetof(struct bpf_tramp_run_ctx, bpf_cookie);
 
-	if (p->aux->sleepable) {
-		enter_prog = (u64)__bpf_prog_enter_sleepable;
-		exit_prog = (u64)__bpf_prog_exit_sleepable;
-	} else {
-		enter_prog = (u64)__bpf_prog_enter;
-		exit_prog = (u64)__bpf_prog_exit;
-	}
+	enter_prog = (u64)bpf_trampoline_enter(p);
+	exit_prog = (u64)bpf_trampoline_exit(p);
 
 	if (l->cookie == 0) {
 		/* if cookie is zero, one instruction is enough to store it */

arch/x86/net/bpf_jit_comp.c

@@ -1894,10 +1894,6 @@ static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
 			   struct bpf_tramp_link *l, int stack_size,
 			   int run_ctx_off, bool save_ret)
 {
-	void (*exit)(struct bpf_prog *prog, u64 start,
-		     struct bpf_tramp_run_ctx *run_ctx) = __bpf_prog_exit;
-	u64 (*enter)(struct bpf_prog *prog,
-		     struct bpf_tramp_run_ctx *run_ctx) = __bpf_prog_enter;
 	u8 *prog = *pprog;
 	u8 *jmp_insn;
 	int ctx_cookie_off = offsetof(struct bpf_tramp_run_ctx, bpf_cookie);
@@ -1916,23 +1912,12 @@ static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
 	 */
 	emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_1, -run_ctx_off + ctx_cookie_off);
 
-	if (p->aux->sleepable) {
-		enter = __bpf_prog_enter_sleepable;
-		exit = __bpf_prog_exit_sleepable;
-	} else if (p->type == BPF_PROG_TYPE_STRUCT_OPS) {
-		enter = __bpf_prog_enter_struct_ops;
-		exit = __bpf_prog_exit_struct_ops;
-	} else if (p->expected_attach_type == BPF_LSM_CGROUP) {
-		enter = __bpf_prog_enter_lsm_cgroup;
-		exit = __bpf_prog_exit_lsm_cgroup;
-	}
-
 	/* arg1: mov rdi, progs[i] */
 	emit_mov_imm64(&prog, BPF_REG_1, (long) p >> 32, (u32) (long) p);
 	/* arg2: lea rsi, [rbp - ctx_cookie_off] */
 	EMIT4(0x48, 0x8D, 0x75, -run_ctx_off);
 
-	if (emit_call(&prog, enter, prog))
+	if (emit_call(&prog, bpf_trampoline_enter(p), prog))
 		return -EINVAL;
 	/* remember prog start time returned by __bpf_prog_enter */
 	emit_mov_reg(&prog, true, BPF_REG_6, BPF_REG_0);
@@ -1977,7 +1962,7 @@ static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
 	emit_mov_reg(&prog, true, BPF_REG_2, BPF_REG_6);
 	/* arg3: lea rdx, [rbp - run_ctx_off] */
 	EMIT4(0x48, 0x8D, 0x55, -run_ctx_off);
-	if (emit_call(&prog, exit, prog))
+	if (emit_call(&prog, bpf_trampoline_exit(p), prog))
 		return -EINVAL;
 
 	*pprog = prog;

include/linux/bpf.h

@@ -854,22 +854,18 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *tr, void *image, void *i
 				const struct btf_func_model *m, u32 flags,
 				struct bpf_tramp_links *tlinks,
 				void *orig_call);
-/* these two functions are called from generated trampoline */
-u64 notrace __bpf_prog_enter(struct bpf_prog *prog, struct bpf_tramp_run_ctx *run_ctx);
-void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start, struct bpf_tramp_run_ctx *run_ctx);
-u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog, struct bpf_tramp_run_ctx *run_ctx);
-void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start,
-				       struct bpf_tramp_run_ctx *run_ctx);
-u64 notrace __bpf_prog_enter_lsm_cgroup(struct bpf_prog *prog,
-					struct bpf_tramp_run_ctx *run_ctx);
-void notrace __bpf_prog_exit_lsm_cgroup(struct bpf_prog *prog, u64 start,
-					struct bpf_tramp_run_ctx *run_ctx);
-u64 notrace __bpf_prog_enter_struct_ops(struct bpf_prog *prog,
-					struct bpf_tramp_run_ctx *run_ctx);
-void notrace __bpf_prog_exit_struct_ops(struct bpf_prog *prog, u64 start,
-					struct bpf_tramp_run_ctx *run_ctx);
+u64 notrace __bpf_prog_enter_sleepable_recur(struct bpf_prog *prog,
+					     struct bpf_tramp_run_ctx *run_ctx);
+void notrace __bpf_prog_exit_sleepable_recur(struct bpf_prog *prog, u64 start,
+					     struct bpf_tramp_run_ctx *run_ctx);
 void notrace __bpf_tramp_enter(struct bpf_tramp_image *tr);
 void notrace __bpf_tramp_exit(struct bpf_tramp_image *tr);
+typedef u64 (*bpf_trampoline_enter_t)(struct bpf_prog *prog,
+				      struct bpf_tramp_run_ctx *run_ctx);
+typedef void (*bpf_trampoline_exit_t)(struct bpf_prog *prog, u64 start,
+				      struct bpf_tramp_run_ctx *run_ctx);
+bpf_trampoline_enter_t bpf_trampoline_enter(const struct bpf_prog *prog);
+bpf_trampoline_exit_t bpf_trampoline_exit(const struct bpf_prog *prog);
 
 struct bpf_ksym {
 	unsigned long		 start;
@@ -2523,7 +2519,9 @@ extern const struct bpf_func_proto bpf_this_cpu_ptr_proto;
 extern const struct bpf_func_proto bpf_ktime_get_coarse_ns_proto;
 extern const struct bpf_func_proto bpf_sock_from_file_proto;
 extern const struct bpf_func_proto bpf_get_socket_ptr_cookie_proto;
+extern const struct bpf_func_proto bpf_task_storage_get_recur_proto;
 extern const struct bpf_func_proto bpf_task_storage_get_proto;
+extern const struct bpf_func_proto bpf_task_storage_delete_recur_proto;
 extern const struct bpf_func_proto bpf_task_storage_delete_proto;
 extern const struct bpf_func_proto bpf_for_each_map_elem_proto;
 extern const struct bpf_func_proto bpf_btf_find_by_name_kind_proto;

include/linux/bpf_verifier.h

@@ -642,10 +642,23 @@ static inline u32 type_flag(u32 type)
 }
 
 /* only use after check_attach_btf_id() */
-static inline enum bpf_prog_type resolve_prog_type(struct bpf_prog *prog)
+static inline enum bpf_prog_type resolve_prog_type(const struct bpf_prog *prog)
 {
 	return prog->type == BPF_PROG_TYPE_EXT ?
 		prog->aux->dst_prog->type : prog->type;
 }
 
+static inline bool bpf_prog_check_recur(const struct bpf_prog *prog)
+{
+	switch (resolve_prog_type(prog)) {
+	case BPF_PROG_TYPE_TRACING:
+		return prog->expected_attach_type != BPF_TRACE_ITER;
+	case BPF_PROG_TYPE_STRUCT_OPS:
+	case BPF_PROG_TYPE_LSM:
+		return false;
+	default:
+		return true;
+	}
+}
+
 #endif /* _LINUX_BPF_VERIFIER_H */

kernel/bpf/bpf_local_storage.c

@@ -242,6 +242,7 @@ void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool use_trace_rcu)
 	__bpf_selem_unlink_storage(selem, use_trace_rcu);
 }
 
+/* If cacheit_lockit is false, this lookup function is lockless */
 struct bpf_local_storage_data *
 bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
 			 struct bpf_local_storage_map *smap,

kernel/bpf/bpf_task_storage.c

@@ -184,14 +184,18 @@ static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key,
 	return err;
 }
 
-static int task_storage_delete(struct task_struct *task, struct bpf_map *map)
+static int task_storage_delete(struct task_struct *task, struct bpf_map *map,
+			       bool nobusy)
 {
 	struct bpf_local_storage_data *sdata;
 
 	sdata = task_storage_lookup(task, map, false);
 	if (!sdata)
 		return -ENOENT;
 
+	if (!nobusy)
+		return -EBUSY;
+
 	bpf_selem_unlink(SELEM(sdata), true);
 
 	return 0;
@@ -220,63 +224,108 @@ static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
 	}
 
 	bpf_task_storage_lock();
-	err = task_storage_delete(task, map);
+	err = task_storage_delete(task, map, true);
 	bpf_task_storage_unlock();
 out:
 	put_pid(pid);
 	return err;
 }
 
-/* *gfp_flags* is a hidden argument provided by the verifier */
-BPF_CALL_5(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
-	   task, void *, value, u64, flags, gfp_t, gfp_flags)
+/* Called by bpf_task_storage_get*() helpers */
+static void *__bpf_task_storage_get(struct bpf_map *map,
+				    struct task_struct *task, void *value,
+				    u64 flags, gfp_t gfp_flags, bool nobusy)
 {
 	struct bpf_local_storage_data *sdata;
 
-	WARN_ON_ONCE(!bpf_rcu_lock_held());
-	if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
-		return (unsigned long)NULL;
-
-	if (!task)
-		return (unsigned long)NULL;
-
-	if (!bpf_task_storage_trylock())
-		return (unsigned long)NULL;
-
-	sdata = task_storage_lookup(task, map, true);
+	sdata = task_storage_lookup(task, map, nobusy);
 	if (sdata)
-		goto unlock;
+		return sdata->data;
 
 	/* only allocate new storage, when the task is refcounted */
 	if (refcount_read(&task->usage) &&
-	    (flags & BPF_LOCAL_STORAGE_GET_F_CREATE))
+	    (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) && nobusy) {
 		sdata = bpf_local_storage_update(
 			task, (struct bpf_local_storage_map *)map, value,
 			BPF_NOEXIST, gfp_flags);
+		return IS_ERR(sdata) ? NULL : sdata->data;
+	}
+
+	return NULL;
+}
 
-unlock:
+/* *gfp_flags* is a hidden argument provided by the verifier */
+BPF_CALL_5(bpf_task_storage_get_recur, struct bpf_map *, map, struct task_struct *,
+	   task, void *, value, u64, flags, gfp_t, gfp_flags)
+{
+	bool nobusy;
+	void *data;
+
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
+	if (flags & ~BPF_LOCAL_STORAGE_GET_F_CREATE || !task)
+		return (unsigned long)NULL;
+
+	nobusy = bpf_task_storage_trylock();
+	data = __bpf_task_storage_get(map, task, value, flags,
+				      gfp_flags, nobusy);
+	if (nobusy)
+		bpf_task_storage_unlock();
+	return (unsigned long)data;
+}
+
+/* *gfp_flags* is a hidden argument provided by the verifier */
+BPF_CALL_5(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
+	   task, void *, value, u64, flags, gfp_t, gfp_flags)
+{
+	void *data;
+
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
+	if (flags & ~BPF_LOCAL_STORAGE_GET_F_CREATE || !task)
+		return (unsigned long)NULL;
+
+	bpf_task_storage_lock();
+	data = __bpf_task_storage_get(map, task, value, flags,
+				      gfp_flags, true);
 	bpf_task_storage_unlock();
-	return IS_ERR_OR_NULL(sdata) ? (unsigned long)NULL :
-		(unsigned long)sdata->data;
+	return (unsigned long)data;
 }
 
-BPF_CALL_2(bpf_task_storage_delete, struct bpf_map *, map, struct task_struct *,
+BPF_CALL_2(bpf_task_storage_delete_recur, struct bpf_map *, map, struct task_struct *,
 	   task)
 {
+	bool nobusy;
 	int ret;
 
 	WARN_ON_ONCE(!bpf_rcu_lock_held());
 	if (!task)
 		return -EINVAL;
 
-	if (!bpf_task_storage_trylock())
-		return -EBUSY;
+	nobusy = bpf_task_storage_trylock();
+	/* This helper must only be called from places where the lifetime of the task
+	 * is guaranteed. Either by being refcounted or by being protected
+	 * by an RCU read-side critical section.
+	 */
+	ret = task_storage_delete(task, map, nobusy);
+	if (nobusy)
+		bpf_task_storage_unlock();
+	return ret;
+}
+
+BPF_CALL_2(bpf_task_storage_delete, struct bpf_map *, map, struct task_struct *,
+	   task)
+{
+	int ret;
+
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
+	if (!task)
+		return -EINVAL;
 
+	bpf_task_storage_lock();
 	/* This helper must only be called from places where the lifetime of the task
 	 * is guaranteed. Either by being refcounted or by being protected
 	 * by an RCU read-side critical section.
 	 */
-	ret = task_storage_delete(task, map);
+	ret = task_storage_delete(task, map, true);
 	bpf_task_storage_unlock();
 	return ret;
 }
@@ -322,6 +371,17 @@ const struct bpf_map_ops task_storage_map_ops = {
 	.map_owner_storage_ptr = task_storage_ptr,
 };
 
+const struct bpf_func_proto bpf_task_storage_get_recur_proto = {
+	.func = bpf_task_storage_get_recur,
+	.gpl_only = false,
+	.ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
+	.arg1_type = ARG_CONST_MAP_PTR,
+	.arg2_type = ARG_PTR_TO_BTF_ID,
+	.arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
+	.arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
+	.arg4_type = ARG_ANYTHING,
+};
+
 const struct bpf_func_proto bpf_task_storage_get_proto = {
 	.func = bpf_task_storage_get,
 	.gpl_only = false,
@@ -333,6 +393,15 @@ const struct bpf_func_proto bpf_task_storage_get_proto = {
 	.arg4_type = ARG_ANYTHING,
 };
 
+const struct bpf_func_proto bpf_task_storage_delete_recur_proto = {
+	.func = bpf_task_storage_delete_recur,
+	.gpl_only = false,
+	.ret_type = RET_INTEGER,
+	.arg1_type = ARG_CONST_MAP_PTR,
+	.arg2_type = ARG_PTR_TO_BTF_ID,
+	.arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
+};
+
 const struct bpf_func_proto bpf_task_storage_delete_proto = {
 	.func = bpf_task_storage_delete,
 	.gpl_only = false,

kernel/bpf/syscall.c

@@ -5133,13 +5133,14 @@ int kern_sys_bpf(int cmd, union bpf_attr *attr, unsigned int size)
 
 		run_ctx.bpf_cookie = 0;
 		run_ctx.saved_run_ctx = NULL;
-		if (!__bpf_prog_enter_sleepable(prog, &run_ctx)) {
+		if (!__bpf_prog_enter_sleepable_recur(prog, &run_ctx)) {
 			/* recursion detected */
 			bpf_prog_put(prog);
 			return -EBUSY;
 		}
 		attr->test.retval = bpf_prog_run(prog, (void *) (long) attr->test.ctx_in);
-		__bpf_prog_exit_sleepable(prog, 0 /* bpf_prog_run does runtime stats */, &run_ctx);
+		__bpf_prog_exit_sleepable_recur(prog, 0 /* bpf_prog_run does runtime stats */,
+						&run_ctx);
 		bpf_prog_put(prog);
 		return 0;
 #endif