bpf: add helpers to support BTF-based kernel data display

.travis.yml

@@ -0,0 +1,33 @@
+sudo: required
+language: bash
+dist: bionic
+services:
+ - docker
+
+env:
+ global:
+ - PROJECT_NAME='libbpf'
+ - AUTHOR_EMAIL="$(git log -1 --pretty=\"%aE\")"
+ - REPO_ROOT="$TRAVIS_BUILD_DIR"
+ - CI_ROOT="$REPO_ROOT/travis-ci"
+ - VMTEST_ROOT="$CI_ROOT/vmtest"
+
+addons:
+ apt:
+ packages:
+ - qemu-kvm
+ - zstd
+ - binutils-dev
+ - elfutils
+ - libcap-dev
+ - libelf-dev
+ - libdw-dev
+ - python3-docutils
+
+jobs:
+ include:
+ - stage: Builds & Tests
+ name: Kernel LATEST + selftests
+ language: bash
+ env: KERNEL=LATEST
+ script: $CI_ROOT/vmtest/run_vmtest.sh || travis_terminate 1

include/linux/bpf.h

@@ -1364,6 +1364,8 @@ int bpf_check(struct bpf_prog **fp, union bpf_attr *attr,
  union bpf_attr __user *uattr);
 void bpf_patch_call_args(struct bpf_insn *insn, u32 stack_depth);
 
+struct btf *bpf_get_btf_vmlinux(void);
+
 /* Map specifics */
 struct xdp_buff;
 struct sk_buff;
@@ -1820,6 +1822,7 @@ extern const struct bpf_func_proto bpf_skc_to_tcp_timewait_sock_proto;
 extern const struct bpf_func_proto bpf_skc_to_tcp_request_sock_proto;
 extern const struct bpf_func_proto bpf_skc_to_udp6_sock_proto;
 extern const struct bpf_func_proto bpf_copy_from_user_proto;
+extern const struct bpf_func_proto bpf_snprintf_btf_proto;
 
 const struct bpf_func_proto *bpf_tracing_func_proto(
 enum bpf_func_id func_id, const struct bpf_prog *prog);

include/linux/btf.h

@@ -6,13 +6,15 @@
 
 #include <linux/types.h>
 #include <uapi/linux/btf.h>
+#include <uapi/linux/bpf.h>
 
 #define BTF_TYPE_EMIT(type) ((void)(type *)0)
 
 struct btf;
 struct btf_member;
 struct btf_type;
 union bpf_attr;
+struct btf_show;
 
 extern const struct file_operations btf_fops;
 
@@ -46,8 +48,45 @@ int btf_get_info_by_fd(const struct btf *btf,
 const struct btf_type *btf_type_id_size(const struct btf *btf,
 u32 *type_id,
 u32 *ret_size);
+
+/*
+ * Options to control show behaviour.
+ *	- BTF_SHOW_COMPACT: no formatting around type information
+ *	- BTF_SHOW_NONAME: no struct/union member names/types
+ *	- BTF_SHOW_PTR_RAW: show raw (unobfuscated) pointer values;
+ * equivalent to %px.
+ *	- BTF_SHOW_ZERO: show zero-valued struct/union members; they
+ * are not displayed by default
+ *	- BTF_SHOW_UNSAFE: skip use of bpf_probe_read() to safely read
+ * data before displaying it.
+ */
+#define BTF_SHOW_COMPACT	BTF_F_COMPACT
+#define BTF_SHOW_NONAME	BTF_F_NONAME
+#define BTF_SHOW_PTR_RAW	BTF_F_PTR_RAW
+#define BTF_SHOW_ZERO	BTF_F_ZERO
+#define BTF_SHOW_UNSAFE	(1ULL << 4)
+
 void btf_type_seq_show(const struct btf *btf, u32 type_id, void *obj,
  struct seq_file *m);
+int btf_type_seq_show_flags(const struct btf *btf, u32 type_id, void *obj,
+ struct seq_file *m, u64 flags);
+
+/*
+ * Copy len bytes of string representation of obj of BTF type_id into buf.
+ *
+ * @btf: struct btf object
+ * @type_id: type id of type obj points to
+ * @obj: pointer to typed data
+ * @buf: buffer to write to
+ * @len: maximum length to write to buf
+ * @flags: show options (see above)
+ *
+ * Return: length that would have been/was copied as per snprintf, or
+ * negative error.
+ */
+int btf_type_snprintf_show(const struct btf *btf, u32 type_id, void *obj,
+ char *buf, int len, u64 flags);
+
 int btf_get_fd_by_id(u32 id);
 u32 btf_id(const struct btf *btf);
 bool btf_member_is_reg_int(const struct btf *btf, const struct btf_type *s,

include/uapi/linux/bpf.h

@@ -3594,6 +3594,50 @@ union bpf_attr {
  *	the data in *dst*. This is a wrapper of **copy_from_user**\ ().
  *	Return
  *	0 on success, or a negative error in case of failure.
+ *
+ * long bpf_snprintf_btf(char *str, u32 str_size, struct btf_ptr *ptr, u32 btf_ptr_size, u64 flags)
+ *	Description
+ *	Use BTF to store a string representation of *ptr*->ptr in *str*,
+ *	using *ptr*->type_id. This value should specify the type
+ *	that *ptr*->ptr points to. LLVM __builtin_btf_type_id(type, 1)
+ *	can be used to look up vmlinux BTF type ids. Traversing the
+ *	data structure using BTF, the type information and values are
+ *	stored in the first *str_size* - 1 bytes of *str*. Safe copy of
+ *	the pointer data is carried out to avoid kernel crashes during
+ *	operation. Smaller types can use string space on the stack;
+ *	larger programs can use map data to store the string
+ *	representation.
+ *
+ *	The string can be subsequently shared with userspace via
+ *	bpf_perf_event_output() or ring buffer interfaces.
+ *	bpf_trace_printk() is to be avoided as it places too small
+ *	a limit on string size to be useful.
+ *
+ *	*flags* is a combination of
+ *
+ *	**BTF_F_COMPACT**
+ *	no formatting around type information
+ *	**BTF_F_NONAME**
+ *	no struct/union member names/types
+ *	**BTF_F_PTR_RAW**
+ *	show raw (unobfuscated) pointer values;
+ *	equivalent to printk specifier %px.
+ *	**BTF_F_ZERO**
+ *	show zero-valued struct/union members; they
+ *	are not displayed by default
+ *
+ *	Return
+ *	The number of bytes that were written (or would have been
+ *	written if output had to be truncated due to string size),
+ *	or a negative error in cases of failure.
+ *
+ * long bpf_seq_printf_btf(struct seq_file *m, struct btf_ptr *ptr, u32 ptr_size, u64 flags)
+ *	Description
+ *	Use BTF to write to seq_write a string representation of
+ *	*ptr*->ptr, using *ptr*->type_id as per bpf_snprintf_btf().
+ *	*flags* are identical to those used for bpf_snprintf_btf.
+ *	Return
+ *	0 on success or a negative error in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)	\
 FN(unspec),	\
@@ -3745,6 +3789,8 @@ union bpf_attr {
 FN(inode_storage_delete),	\
 FN(d_path),	\
 FN(copy_from_user),	\
+FN(snprintf_btf),	\
+FN(seq_printf_btf),	\
 /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -4853,4 +4899,34 @@ struct bpf_sk_lookup {
 __u32 local_port;	/* Host byte order */
 };
 
+/*
+ * struct btf_ptr is used for typed pointer representation; the
+ * type id is used to render the pointer data as the appropriate type
+ * via the bpf_snprintf_btf() helper described above. A flags field -
+ * potentially to specify additional details about the BTF pointer
+ * (rather than its mode of display) - is included for future use.
+ * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately.
+ */
+struct btf_ptr {
+void *ptr;
+__u32 type_id;
+__u32 flags;	/* BTF ptr flags; unused at present. */
+};
+
+/*
+ * Flags to control bpf_snprintf_btf() behaviour.
+ * - BTF_F_COMPACT: no formatting around type information
+ * - BTF_F_NONAME: no struct/union member names/types
+ * - BTF_F_PTR_RAW: show raw (unobfuscated) pointer values;
+ * equivalent to %px.
+ * - BTF_F_ZERO: show zero-valued struct/union members; they
+ * are not displayed by default
+ */
+enum {
+BTF_F_COMPACT	=	(1ULL << 0),
+BTF_F_NONAME	=	(1ULL << 1),
+BTF_F_PTR_RAW	=	(1ULL << 2),
+BTF_F_ZERO	=	(1ULL << 3),
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */

kernel/bpf/bpf_iter.c

@@ -88,8 +88,8 @@ static ssize_t bpf_seq_read(struct file *file, char __user *buf, size_t size,
 mutex_lock(&seq->lock);
 
 if (!seq->buf) {
-seq->size = PAGE_SIZE;
-seq->buf = kmalloc(seq->size, GFP_KERNEL);
+seq->size = PAGE_SIZE << 3;
+seq->buf = kvmalloc(seq->size, GFP_KERNEL);
 if (!seq->buf) {
 err = -ENOMEM;
 goto done;