bpf: Enable non-atomic allocations in local storage

Currently, local storage memory can only be allocated atomically
(GFP_ATOMIC). This restriction is too strict for sleepable bpf
programs.

In this patch, the verifier detects whether the program is sleepable,
and passes the corresponding GFP_KERNEL or GFP_ATOMIC flag as a
5th argument to bpf_task/sk/inode_storage_get. This flag will propagate
down to the local storage functions that allocate memory.

Please note that bpf_task/sk/inode_storage_update_elem functions are
invoked by userspace applications through syscalls. Preemption is
disabled before bpf_task/sk/inode_storage_update_elem is called, which
means they will always have to allocate memory atomically.
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: KP Singh <kpsingh@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220318045553.3091807-2-joannekoong@fb.com

include/linux/bpf_local_storage.h

@@ -154,16 +154,17 @@ void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem);
 
 struct bpf_local_storage_elem *
 bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner, void *value,
-		bool charge_mem);
+		bool charge_mem, gfp_t gfp_flags);
 
 int
 bpf_local_storage_alloc(void *owner,
 			struct bpf_local_storage_map *smap,
-			struct bpf_local_storage_elem *first_selem);
+			struct bpf_local_storage_elem *first_selem,
+			gfp_t gfp_flags);
 
 struct bpf_local_storage_data *
 bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
-			 void *value, u64 map_flags);
+			 void *value, u64 map_flags, gfp_t gfp_flags);
 
 void bpf_local_storage_free_rcu(struct rcu_head *rcu);
 

kernel/bpf/bpf_inode_storage.c

@@ -136,7 +136,7 @@ static int bpf_fd_inode_storage_update_elem(struct bpf_map *map, void *key,
 
 	sdata = bpf_local_storage_update(f->f_inode,
 					 (struct bpf_local_storage_map *)map,
-					 value, map_flags);
+					 value, map_flags, GFP_ATOMIC);
 	fput(f);
 	return PTR_ERR_OR_ZERO(sdata);
 }
@@ -169,8 +169,9 @@ static int bpf_fd_inode_storage_delete_elem(struct bpf_map *map, void *key)
 	return err;
 }
 
-BPF_CALL_4(bpf_inode_storage_get, struct bpf_map *, map, struct inode *, inode,
-	   void *, value, u64, flags)
+/* *gfp_flags* is a hidden argument provided by the verifier */
+BPF_CALL_5(bpf_inode_storage_get, struct bpf_map *, map, struct inode *, inode,
+	   void *, value, u64, flags, gfp_t, gfp_flags)
 {
 	struct bpf_local_storage_data *sdata;
 
@@ -196,7 +197,7 @@ BPF_CALL_4(bpf_inode_storage_get, struct bpf_map *, map, struct inode *, inode,
 	if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
 		sdata = bpf_local_storage_update(
 			inode, (struct bpf_local_storage_map *)map, value,
-			BPF_NOEXIST);
+			BPF_NOEXIST, gfp_flags);
 		return IS_ERR(sdata) ? (unsigned long)NULL :
 					     (unsigned long)sdata->data;
 	}

kernel/bpf/bpf_local_storage.c

@@ -63,7 +63,7 @@ static bool selem_linked_to_map(const struct bpf_local_storage_elem *selem)
 
 struct bpf_local_storage_elem *
 bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
-		void *value, bool charge_mem)
+		void *value, bool charge_mem, gfp_t gfp_flags)
 {
 	struct bpf_local_storage_elem *selem;
 
@@ -71,7 +71,7 @@ bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
 		return NULL;
 
 	selem = bpf_map_kzalloc(&smap->map, smap->elem_size,
-				GFP_ATOMIC | __GFP_NOWARN);
+				gfp_flags | __GFP_NOWARN);
 	if (selem) {
 		if (value)
 			memcpy(SDATA(selem)->data, value, smap->map.value_size);
@@ -282,7 +282,8 @@ static int check_flags(const struct bpf_local_storage_data *old_sdata,
 
 int bpf_local_storage_alloc(void *owner,
 			    struct bpf_local_storage_map *smap,
-			    struct bpf_local_storage_elem *first_selem)
+			    struct bpf_local_storage_elem *first_selem,
+			    gfp_t gfp_flags)
 {
 	struct bpf_local_storage *prev_storage, *storage;
 	struct bpf_local_storage **owner_storage_ptr;
@@ -293,7 +294,7 @@ int bpf_local_storage_alloc(void *owner,
 		return err;
 
 	storage = bpf_map_kzalloc(&smap->map, sizeof(*storage),
-				  GFP_ATOMIC | __GFP_NOWARN);
+				  gfp_flags | __GFP_NOWARN);
 	if (!storage) {
 		err = -ENOMEM;
 		goto uncharge;
@@ -350,10 +351,10 @@ int bpf_local_storage_alloc(void *owner,
  */
 struct bpf_local_storage_data *
 bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
-			 void *value, u64 map_flags)
+			 void *value, u64 map_flags, gfp_t gfp_flags)
 {
 	struct bpf_local_storage_data *old_sdata = NULL;
-	struct bpf_local_storage_elem *selem;
+	struct bpf_local_storage_elem *selem = NULL;
 	struct bpf_local_storage *local_storage;
 	unsigned long flags;
 	int err;
@@ -365,6 +366,9 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 		     !map_value_has_spin_lock(&smap->map)))
 		return ERR_PTR(-EINVAL);
 
+	if (gfp_flags == GFP_KERNEL && (map_flags & ~BPF_F_LOCK) != BPF_NOEXIST)
+		return ERR_PTR(-EINVAL);
+
 	local_storage = rcu_dereference_check(*owner_storage(smap, owner),
 					      bpf_rcu_lock_held());
 	if (!local_storage || hlist_empty(&local_storage->list)) {
@@ -373,11 +377,11 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 		if (err)
 			return ERR_PTR(err);
 
-		selem = bpf_selem_alloc(smap, owner, value, true);
+		selem = bpf_selem_alloc(smap, owner, value, true, gfp_flags);
 		if (!selem)
 			return ERR_PTR(-ENOMEM);
 
-		err = bpf_local_storage_alloc(owner, smap, selem);
+		err = bpf_local_storage_alloc(owner, smap, selem, gfp_flags);
 		if (err) {
 			kfree(selem);
 			mem_uncharge(smap, owner, smap->elem_size);
@@ -404,6 +408,12 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 		}
 	}
 
+	if (gfp_flags == GFP_KERNEL) {
+		selem = bpf_selem_alloc(smap, owner, value, true, gfp_flags);
+		if (!selem)
+			return ERR_PTR(-ENOMEM);
+	}
+
 	raw_spin_lock_irqsave(&local_storage->lock, flags);
 
 	/* Recheck local_storage->list under local_storage->lock */
@@ -429,6 +439,7 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 		goto unlock;
 	}
 
+	if (gfp_flags != GFP_KERNEL) {
 		/* local_storage->lock is held.  Hence, we are sure
 		 * we can unlink and uncharge the old_sdata successfully
 		 * later.  Hence, instead of charging the new selem now
@@ -438,11 +449,12 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 		 * old_sdata will not be uncharged later during
 		 * bpf_selem_unlink_storage_nolock().
 		 */
-	selem = bpf_selem_alloc(smap, owner, value, !old_sdata);
+		selem = bpf_selem_alloc(smap, owner, value, !old_sdata, gfp_flags);
 		if (!selem) {
 			err = -ENOMEM;
 			goto unlock_err;
 		}
+	}
 
 	/* First, link the new selem to the map */
 	bpf_selem_link_map(smap, selem);
@@ -463,6 +475,10 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 
 unlock_err:
 	raw_spin_unlock_irqrestore(&local_storage->lock, flags);
+	if (selem) {
+		mem_uncharge(smap, owner, smap->elem_size);
+		kfree(selem);
+	}
 	return ERR_PTR(err);
 }
 

kernel/bpf/bpf_task_storage.c

@@ -174,7 +174,8 @@ static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key,
 
 	bpf_task_storage_lock();
 	sdata = bpf_local_storage_update(
-		task, (struct bpf_local_storage_map *)map, value, map_flags);
+		task, (struct bpf_local_storage_map *)map, value, map_flags,
+		GFP_ATOMIC);
 	bpf_task_storage_unlock();
 
 	err = PTR_ERR_OR_ZERO(sdata);
@@ -226,8 +227,9 @@ static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
 	return err;
 }
 
-BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
-	   task, void *, value, u64, flags)
+/* *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)
 {
 	struct bpf_local_storage_data *sdata;
 
@@ -250,7 +252,7 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
 	    (flags & BPF_LOCAL_STORAGE_GET_F_CREATE))
 		sdata = bpf_local_storage_update(
 			task, (struct bpf_local_storage_map *)map, value,
-			BPF_NOEXIST);
+			BPF_NOEXIST, gfp_flags);
 
 unlock:
 	bpf_task_storage_unlock();

kernel/bpf/verifier.c

@@ -13492,6 +13492,26 @@ 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) {
+			if (env->prog->aux->sleepable)
+				insn_buf[0] = BPF_MOV64_IMM(BPF_REG_5, (__s32)GFP_KERNEL);
+			else
+				insn_buf[0] = BPF_MOV64_IMM(BPF_REG_5, (__s32)GFP_ATOMIC);
+			insn_buf[1] = *insn;
+			cnt = 2;
+
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
+			if (!new_prog)
+				return -ENOMEM;
+
+			delta += cnt - 1;
+			env->prog = prog = new_prog;
+			insn = new_prog->insnsi + i + delta;
+			goto patch_call_imm;
+		}
+
 		/* BPF_EMIT_CALL() assumptions in some of the map_gen_lookup
 		 * and other inlining handlers are currently limited to 64 bit
 		 * only.

net/core/bpf_sk_storage.c

@@ -141,7 +141,7 @@ static int bpf_fd_sk_storage_update_elem(struct bpf_map *map, void *key,
 	if (sock) {
 		sdata = bpf_local_storage_update(
 			sock->sk, (struct bpf_local_storage_map *)map, value,
-			map_flags);
+			map_flags, GFP_ATOMIC);
 		sockfd_put(sock);
 		return PTR_ERR_OR_ZERO(sdata);
 	}
@@ -172,7 +172,7 @@ bpf_sk_storage_clone_elem(struct sock *newsk,
 {
 	struct bpf_local_storage_elem *copy_selem;
 
-	copy_selem = bpf_selem_alloc(smap, newsk, NULL, true);
+	copy_selem = bpf_selem_alloc(smap, newsk, NULL, true, GFP_ATOMIC);
 	if (!copy_selem)
 		return NULL;
 
@@ -230,7 +230,7 @@ int bpf_sk_storage_clone(const struct sock *sk, struct sock *newsk)
 			bpf_selem_link_map(smap, copy_selem);
 			bpf_selem_link_storage_nolock(new_sk_storage, copy_selem);
 		} else {
-			ret = bpf_local_storage_alloc(newsk, smap, copy_selem);
+			ret = bpf_local_storage_alloc(newsk, smap, copy_selem, GFP_ATOMIC);
 			if (ret) {
 				kfree(copy_selem);
 				atomic_sub(smap->elem_size,
@@ -255,8 +255,9 @@ int bpf_sk_storage_clone(const struct sock *sk, struct sock *newsk)
 	return ret;
 }
 
-BPF_CALL_4(bpf_sk_storage_get, struct bpf_map *, map, struct sock *, sk,
-	   void *, value, u64, flags)
+/* *gfp_flags* is a hidden argument provided by the verifier */
+BPF_CALL_5(bpf_sk_storage_get, struct bpf_map *, map, struct sock *, sk,
+	   void *, value, u64, flags, gfp_t, gfp_flags)
 {
 	struct bpf_local_storage_data *sdata;
 
@@ -277,7 +278,7 @@ BPF_CALL_4(bpf_sk_storage_get, struct bpf_map *, map, struct sock *, sk,
 	    refcount_inc_not_zero(&sk->sk_refcnt)) {
 		sdata = bpf_local_storage_update(
 			sk, (struct bpf_local_storage_map *)map, value,
-			BPF_NOEXIST);
+			BPF_NOEXIST, gfp_flags);
 		/* sk must be a fullsock (guaranteed by verifier),
 		 * so sock_gen_put() is unnecessary.
 		 */
@@ -417,14 +418,16 @@ static bool bpf_sk_storage_tracing_allowed(const struct bpf_prog *prog)
 	return false;
 }
 
-BPF_CALL_4(bpf_sk_storage_get_tracing, struct bpf_map *, map, struct sock *, sk,
-	   void *, value, u64, flags)
+/* *gfp_flags* is a hidden argument provided by the verifier */
+BPF_CALL_5(bpf_sk_storage_get_tracing, struct bpf_map *, map, struct sock *, sk,
+	   void *, value, u64, flags, gfp_t, gfp_flags)
 {
 	WARN_ON_ONCE(!bpf_rcu_lock_held());
 	if (in_hardirq() || in_nmi())
 		return (unsigned long)NULL;
 
-	return (unsigned long)____bpf_sk_storage_get(map, sk, value, flags);
+	return (unsigned long)____bpf_sk_storage_get(map, sk, value, flags,
+						     gfp_flags);
 }
 
 BPF_CALL_2(bpf_sk_storage_delete_tracing, struct bpf_map *, map,