netdev - [RFC PATCH bpf-next 2/5] bpf: assign ID to vmlinux BTF and return extra info for BTF in GET_OBJ

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Message-ID: <20201105045140.2589346-3-andrii@kernel.org>
Date:   Wed, 4 Nov 2020 20:51:37 -0800
From:   Andrii Nakryiko <andrii@...nel.org>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii@...nel.org>, <kernel-team@...com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [RFC PATCH bpf-next 2/5] bpf: assign ID to vmlinux BTF and return extra info for BTF in GET_OBJ_INFO

Allocate ID for vmlinux BTF. This makes it visible when iterating over all
BTF objects in the system. To allow distinguishing vmlinux BTF (and later
kernel module BTF) from user-provided BTFs, expose extra kernel_btf flag, as
well as BTF name (empty for vmlinux BTF, but will be used for kernel module
BTF). We might want to later allow specifying BTF name for user-provided BTFs
as well, if that makes sense. But currently this is reserved only for
in-kernel BTFs.

Having in-kernel BTFs exposed IDs will allow to extend BPF APIs that require
in-kernel BTF type with ability to specify BTF types from kernel modules, not
just vmlinux BTF. This will be implemented in a follow up patch set for
fentry/fexit/fmod_ret/lsm/etc.

Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
---
 include/uapi/linux/bpf.h       |  3 +++
 kernel/bpf/btf.c               | 38 ++++++++++++++++++++++++++++++++--
 tools/include/uapi/linux/bpf.h |  3 +++
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e6ceac3f7d62..7955b144f267 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4418,6 +4418,9 @@ struct bpf_btf_info {
 	__aligned_u64 btf;
 	__u32 btf_size;
 	__u32 id;
+	__aligned_u64 name;
+	__u32 name_len;
+	__u32 kernel_btf;
 } __attribute__((aligned(8)));
 
 struct bpf_link_info {
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index f61944a3873b..6a99677e57c0 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -215,6 +215,8 @@ struct btf {
 	struct btf *base_btf;
 	u32 start_id; /* first type ID in this BTF (0 for base BTF) */
 	u32 start_str_off; /* first string offset (0 for base BTF) */
+	char name[MODULE_NAME_LEN];
+	bool kernel_btf;
 };
 
 enum verifier_phase {
@@ -4441,6 +4443,7 @@ struct btf *btf_parse_vmlinux(void)
 
 	btf->data = __start_BTF;
 	btf->data_size = __stop_BTF - __start_BTF;
+	btf->kernel_btf = true;
 
 	err = btf_parse_hdr(env);
 	if (err)
@@ -4466,8 +4469,13 @@ struct btf *btf_parse_vmlinux(void)
 
 	bpf_struct_ops_init(btf, log);
 
-	btf_verifier_env_free(env);
 	refcount_set(&btf->refcnt, 1);
+
+	err = btf_alloc_id(btf);
+	if (err)
+		goto errout;
+
+	btf_verifier_env_free(env);
 	return btf;
 
 errout:
@@ -5565,7 +5573,8 @@ int btf_get_info_by_fd(const struct btf *btf,
 	struct bpf_btf_info info;
 	u32 info_copy, btf_copy;
 	void __user *ubtf;
-	u32 uinfo_len;
+	char __user *uname;
+	u32 uinfo_len, uname_len, name_len;
 
 	uinfo = u64_to_user_ptr(attr->info.info);
 	uinfo_len = attr->info.info_len;
@@ -5582,6 +5591,31 @@ int btf_get_info_by_fd(const struct btf *btf,
 		return -EFAULT;
 	info.btf_size = btf->data_size;
 
+	info.kernel_btf = btf->kernel_btf;
+
+	uname = u64_to_user_ptr(info.name);
+	uname_len = info.name_len;
+	if (!uname ^ !uname_len)
+		return -EINVAL;
+
+	name_len = strlen(btf->name);
+	info.name_len = name_len;
+
+	if (uname) {
+		if (uname_len >= name_len + 1) {
+			if (copy_to_user(uname, btf->name, name_len + 1))
+				return -EFAULT;
+		} else {
+			char zero = '\0';
+
+			if (copy_to_user(uname, btf->name, uname_len - 1))
+				return -EFAULT;
+			if (put_user(zero, uname + uname_len - 1))
+				return -EFAULT;
+			return -ENOSPC;
+		}
+	}
+
 	if (copy_to_user(uinfo, &info, info_copy) ||
 	    put_user(info_copy, &uattr->info.info_len))
 		return -EFAULT;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e6ceac3f7d62..7955b144f267 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4418,6 +4418,9 @@ struct bpf_btf_info {
 	__aligned_u64 btf;
 	__u32 btf_size;
 	__u32 id;
+	__aligned_u64 name;
+	__u32 name_len;
+	__u32 kernel_btf;
 } __attribute__((aligned(8)));
 
 struct bpf_link_info {
-- 
2.24.1