[PATCH bpf-next v2 05/15] bpf: Allow storing percpu kptr in map

From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
To: bpf@vger.kernel.org
Cc: "Hao Luo" <haoluo@google.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Jesper Dangaard Brouer" <brouer@redhat.com>
Subject: [PATCH bpf-next v2 05/15] bpf: Allow storing percpu kptr in map
Date: Thu, 17 Mar 2022 17:29:47 +0530	[thread overview]
Message-ID: <20220317115957.3193097-6-memxor@gmail.com> (raw)
In-Reply-To: <20220317115957.3193097-1-memxor@gmail.com>

Make adjustments to the code to allow storing percpu PTR_TO_BTF_ID in a
map. Similar to 'kptr_ref' tag, a new 'kptr_percpu' allows tagging types
of pointers accepting stores of such register types. On load, verifier
marks destination register as having type PTR_TO_BTF_ID | MEM_PERCPU |
PTR_MAYBE_NULL.

Cc: Hao Luo <haoluo@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf.h   |  3 ++-
 kernel/bpf/btf.c      | 13 ++++++++++---
 kernel/bpf/verifier.c | 26 +++++++++++++++++++++-----
 3 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 702aa882e4a3..433f5cb161cf 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -161,7 +161,8 @@ enum {
 };
 
 enum {
-	BPF_MAP_VALUE_OFF_F_REF = (1U << 0),
+	BPF_MAP_VALUE_OFF_F_REF    = (1U << 0),
+	BPF_MAP_VALUE_OFF_F_PERCPU = (1U << 1),
 };
 
 struct bpf_map_value_off_desc {
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 7b4179667bf1..04d604931f59 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3197,7 +3197,7 @@ static int btf_find_field_kptr(const struct btf *btf, const struct btf_type *t,
 			       u32 off, int sz, struct btf_field_info *info,
 			       int info_cnt, int idx)
 {
-	bool kptr_tag = false, kptr_ref_tag = false;
+	bool kptr_tag = false, kptr_ref_tag = false, kptr_percpu_tag = false;
 	int tags;
 
 	/* For PTR, sz is always == 8 */
@@ -3216,12 +3216,17 @@ static int btf_find_field_kptr(const struct btf *btf, const struct btf_type *t,
 			if (kptr_ref_tag)
 				return -EEXIST;
 			kptr_ref_tag = true;
+		} else if (!strcmp("kptr_percpu", __btf_name_by_offset(btf, t->name_off))) {
+			/* repeated tag */
+			if (kptr_percpu_tag)
+				return -EEXIST;
+			kptr_percpu_tag = true;
 		}
 		/* Look for next tag */
 		t = btf_type_by_id(btf, t->type);
 	}
 
-	tags = kptr_tag + kptr_ref_tag;
+	tags = kptr_tag + kptr_ref_tag + kptr_percpu_tag;
 	if (!tags)
 		return BTF_FIELD_IGNORE;
 	else if (tags > 1)
@@ -3236,7 +3241,9 @@ static int btf_find_field_kptr(const struct btf *btf, const struct btf_type *t,
 
 	if (idx >= info_cnt)
 		return -E2BIG;
-	if (kptr_ref_tag)
+	if (kptr_percpu_tag)
+		info[idx].flags = BPF_MAP_VALUE_OFF_F_PERCPU;
+	else if (kptr_ref_tag)
 		info[idx].flags = BPF_MAP_VALUE_OFF_F_REF;
 	else
 		info[idx].flags = 0;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f8738054aa52..cc8f7250e43e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3517,11 +3517,19 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
 			       bool ref_ptr)
 {
 	const char *targ_name = kernel_type_name(off_desc->btf, off_desc->btf_id);
+	enum bpf_reg_type reg_type;
 	const char *reg_name = "";
 	bool fixed_off_ok = true;
 
-	if (reg->type != PTR_TO_BTF_ID && reg->type != PTR_TO_BTF_ID_OR_NULL)
-		goto bad_type;
+	if (off_desc->flags & BPF_MAP_VALUE_OFF_F_PERCPU) {
+		if (reg->type != (PTR_TO_BTF_ID | MEM_PERCPU) &&
+		    reg->type != (PTR_TO_BTF_ID | PTR_MAYBE_NULL | MEM_PERCPU))
+			goto bad_type;
+	} else { /* referenced and unreferenced case */
+		if (reg->type != PTR_TO_BTF_ID &&
+		    reg->type != (PTR_TO_BTF_ID | PTR_MAYBE_NULL))
+			goto bad_type;
+	}
 
 	if (!btf_is_kernel(reg->btf)) {
 		verbose(env, "R%d must point to kernel BTF\n", regno);
@@ -3557,9 +3565,13 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
 		goto bad_type;
 	return 0;
 bad_type:
+	if (off_desc->flags & BPF_MAP_VALUE_OFF_F_PERCPU)
+		reg_type = PTR_TO_BTF_ID | PTR_MAYBE_NULL | MEM_PERCPU;
+	else
+		reg_type = PTR_TO_BTF_ID | PTR_MAYBE_NULL;
 	verbose(env, "invalid kptr access, R%d type=%s%s ", regno,
 		reg_type_str(env, reg->type), reg_name);
-	verbose(env, "expected=%s%s\n", reg_type_str(env, PTR_TO_BTF_ID), targ_name);
+	verbose(env, "expected=%s%s\n", reg_type_str(env, reg_type), targ_name);
 	return -EINVAL;
 }
 
@@ -3572,10 +3584,11 @@ static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
 {
 	struct bpf_reg_state *reg = reg_state(env, regno), *val_reg;
 	struct bpf_insn *insn = &env->prog->insnsi[insn_idx];
+	enum bpf_type_flag reg_flags = PTR_MAYBE_NULL;
+	bool ref_ptr = false, percpu_ptr = false;
 	struct bpf_map_value_off_desc *off_desc;
 	int insn_class = BPF_CLASS(insn->code);
 	struct bpf_map *map = reg->map_ptr;
-	bool ref_ptr = false;
 
 	/* Things we already checked for in check_map_access:
 	 *  - Reject cases where variable offset may touch BTF ID pointer
@@ -3601,6 +3614,9 @@ static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
 	}
 
 	ref_ptr = off_desc->flags & BPF_MAP_VALUE_OFF_F_REF;
+	percpu_ptr = off_desc->flags & BPF_MAP_VALUE_OFF_F_PERCPU;
+	if (percpu_ptr)
+		reg_flags |= MEM_PERCPU;
 
 	if (insn_class == BPF_LDX) {
 		if (WARN_ON_ONCE(value_regno < 0))
@@ -3614,7 +3630,7 @@ static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
 		 * value from map as PTR_TO_BTF_ID, with the correct type.
 		 */
 		mark_btf_ld_reg(env, cur_regs(env), value_regno, PTR_TO_BTF_ID, off_desc->btf,
-				off_desc->btf_id, PTR_MAYBE_NULL);
+				off_desc->btf_id, reg_flags);
 		val_reg->id = ++env->id_gen;
 	} else if (insn_class == BPF_STX) {
 		if (WARN_ON_ONCE(value_regno < 0))
-- 
2.35.1

