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 ("vmlinux" for vmlinux BTF, will equal to module's name for 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@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20201110011932.3201430-3-andrii@kernel.org

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 9879d6793e9045675420be644c13554916a45c5c..162999b12790138d5d231548f7f86bf57bcd96b7 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4466,6 +4466,9 @@ 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 727c1c27053fdb18272a4d3dea8245ab8e8ebbeb..856585db7aa72c75d928112c5aa0abbdb7c85fa5 100644 (file)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -214,6 +214,8 @@ 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 {
@@ -4429,6 +4431,8 @@ struct btf *btf_parse_vmlinux(void)
 
        btf->data = __start_BTF;
        btf->data_size = __stop_BTF - __start_BTF;
+       btf->kernel_btf = true;
+       snprintf(btf->name, sizeof(btf->name), "vmlinux");
 
        err = btf_parse_hdr(env);
        if (err)
@@ -4454,8 +4458,13 @@ 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:
@@ -5553,7 +5562,9 @@ 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;
+       int ret = 0;
 
        uinfo = u64_to_user_ptr(attr->info.info);
        uinfo_len = attr->info.info_len;
@@ -5570,11 +5581,37 @@ 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;
+                       /* let user-space know about too short buffer */
+                       ret = -ENOSPC;
+               }
+       }
+
        if (copy_to_user(uinfo, &info, info_copy) ||
            put_user(info_copy, &uattr->info.info_len))
                return -EFAULT;
 
-       return 0;
+       return ret;
 }
 
 int btf_get_fd_by_id(u32 id)

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 9879d6793e9045675420be644c13554916a45c5c..162999b12790138d5d231548f7f86bf57bcd96b7 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4466,6 +4466,9 @@ 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 {