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

4 files changed, 68 insertions, 29 deletions

diff --git a/kernel/bpf/bpf_inode_storage.c b/kernel/bpf/bpf_inode_storage.c
index e29d9e3d853e..96be8d518885 100644
--- a/kernel/bpf/bpf_inode_storage.c
+++ b/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;
 	}
diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index 092a1ac772d7..01aa2b51ec4d 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/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 @@ uncharge:
  */
 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 */
@@ -429,19 +439,21 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 		goto unlock;
 	}
 
-	/* 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
-	 * and then uncharge the old selem later (which may cause
-	 * a potential but unnecessary charge failure),  avoid taking
-	 * a charge at all here (the "!old_sdata" check) and the
-	 * old_sdata will not be uncharged later during
-	 * bpf_selem_unlink_storage_nolock().
-	 */
-	selem = bpf_selem_alloc(smap, owner, value, !old_sdata);
-	if (!selem) {
-		err = -ENOMEM;
-		goto unlock_err;
+	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
+		 * and then uncharge the old selem later (which may cause
+		 * a potential but unnecessary charge failure),  avoid taking
+		 * a charge at all here (the "!old_sdata" check) and the
+		 * old_sdata will not be uncharged later during
+		 * bpf_selem_unlink_storage_nolock().
+		 */
+		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 */
@@ -463,6 +475,10 @@ unlock:
 
 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);
 }
 
diff --git a/kernel/bpf/bpf_task_storage.c b/kernel/bpf/bpf_task_storage.c
index 5da7bed0f5f6..6638a0ecc3d2 100644
--- a/kernel/bpf/bpf_task_storage.c
+++ b/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 @@ out:
 	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();
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0287176bfe9a..6347dcdee1fd 100644
--- a/kernel/bpf/verifier.c
+++ b/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.