[PATCH bpf-next 0/4] introduce bpf_iter for task_vma

[PATCH bpf-next 0/4] introduce bpf_iter for task_vma

[Song Liu]

This set introduces bpf_iter for task_vma, which can be used to generate
information similar to /proc/pid/maps or /proc/pid/smaps. Patch 4/4 adds
an example that mimics /proc/pid/maps.

Song Liu (4):
  bpf: introduce task_vma bpf_iter
  bpf: allow bpf_d_path in sleepable bpf_iter program
  libbpf: introduce section "iter.s/" for sleepable bpf_iter program
  selftests/bpf: add test for bpf_iter_task_vma

 include/linux/bpf.h                           |   2 +-
 include/uapi/linux/bpf.h                      |   7 +
 kernel/bpf/task_iter.c                        | 193 +++++++++++++++++-
 kernel/trace/bpf_trace.c                      |   5 +
 tools/lib/bpf/libbpf.c                        |   5 +
 .../selftests/bpf/prog_tests/bpf_iter.c       | 106 +++++++++-
 tools/testing/selftests/bpf/progs/bpf_iter.h  |   9 +
 .../selftests/bpf/progs/bpf_iter_task_vma.c   |  55 +++++
 8 files changed, 370 insertions(+), 12 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c

--
2.24.1

[PATCH bpf-next 1/4] bpf: introduce task_vma bpf_iter

[Song Liu]

Introduce task_vma bpf_iter to print memory information of a process. It
can be used to print customized information similar to /proc/<pid>/maps.

task_vma iterator releases mmap_lock before calling the BPF program.
Therefore, we cannot pass vm_area_struct directly to the BPF program. A
new __vm_area_struct is introduced to keep key information of a vma. On
each iteration, task_vma gathers information in __vm_area_struct and
passes it to the BPF program.

If the vma maps to a file, task_vma also holds a reference to the file
while calling the BPF program.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 include/linux/bpf.h      |   2 +-
 include/uapi/linux/bpf.h |   7 ++
 kernel/bpf/task_iter.c   | 193 ++++++++++++++++++++++++++++++++++++++-
 3 files changed, 200 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 07cb5d15e7439..49dd1e29c8118 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1325,7 +1325,7 @@ enum bpf_iter_feature {
 	BPF_ITER_RESCHED	= BIT(0),
 };
 
-#define BPF_ITER_CTX_ARG_MAX 2
+#define BPF_ITER_CTX_ARG_MAX 3
 struct bpf_iter_reg {
 	const char *target;
 	bpf_iter_attach_target_t attach_target;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 30b477a264827..c2db8a1d0cbd2 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5151,4 +5151,11 @@ enum {
 	BTF_F_ZERO	=	(1ULL << 3),
 };
 
+struct __vm_area_struct {
+	__u64 start;
+	__u64 end;
+	__u64 flags;
+	__u64 pgoff;
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 0458a40edf10a..30e5475d0831e 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -304,9 +304,171 @@ static const struct seq_operations task_file_seq_ops = {
 	.show	= task_file_seq_show,
 };
 
+struct bpf_iter_seq_task_vma_info {
+	/* The first field must be struct bpf_iter_seq_task_common.
+	 * this is assumed by {init, fini}_seq_pidns() callback functions.
+	 */
+	struct bpf_iter_seq_task_common common;
+	struct task_struct *task;
+	struct __vm_area_struct vma;
+	struct file *file;
+	u32 tid;
+};
+
+static struct __vm_area_struct *
+task_vma_seq_get_next(struct bpf_iter_seq_task_vma_info *info)
+{
+	struct pid_namespace *ns = info->common.ns;
+	struct task_struct *curr_task;
+	struct vm_area_struct *vma;
+	u32 curr_tid = info->tid;
+	bool new_task = false;
+
+	/* If this function returns a non-NULL vma, it held a reference to
+	 * the task_struct. If info->file is non-NULL, it also holds a
+	 * reference to the file. Otherwise, it does not hold any
+	 * reference.
+	 */
+again:
+	if (info->task) {
+		curr_task = info->task;
+	} else {
+		curr_task = task_seq_get_next(ns, &curr_tid, true);
+		if (!curr_task) {
+			info->task = NULL;
+			return NULL;
+		}
+
+		if (curr_tid != info->tid) {
+			info->tid = curr_tid;
+			new_task = true;
+		}
+
+		if (!curr_task->mm)
+			goto next_task;
+		info->task = curr_task;
+	}
+
+	mmap_read_lock(curr_task->mm);
+	if (new_task) {
+		vma = curr_task->mm->mmap;
+	} else {
+		/* We drop the lock between each iteration, so it is
+		 * necessary to use find_vma() to find the next vma. This
+		 * is similar to the mechanism in show_smaps_rollup().
+		 */
+		vma = find_vma(curr_task->mm, info->vma.end - 1);
+		/* same vma as previous iteration, use vma->next */
+		if (vma && (vma->vm_start == info->vma.start))
+			vma = vma->vm_next;
+	}
+	if (!vma) {
+		mmap_read_unlock(curr_task->mm);
+		goto next_task;
+	}
+	info->task = curr_task;
+	info->vma.start = vma->vm_start;
+	info->vma.end = vma->vm_end;
+	info->vma.pgoff = vma->vm_pgoff;
+	info->vma.flags = vma->vm_flags;
+	if (vma->vm_file)
+		info->file = get_file(vma->vm_file);
+	mmap_read_unlock(curr_task->mm);
+	return &info->vma;
+
+next_task:
+	put_task_struct(curr_task);
+	info->task = NULL;
+	curr_tid = ++(info->tid);
+	goto again;
+}
+
+static void *task_vma_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	struct bpf_iter_seq_task_vma_info *info = seq->private;
+	struct __vm_area_struct *vma;
+
+	info->task = NULL;
+	vma = task_vma_seq_get_next(info);
+	if (vma && *pos == 0)
+		++*pos;
+
+	return vma;
+}
+
+static void *task_vma_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	struct bpf_iter_seq_task_vma_info *info = seq->private;
+
+	++*pos;
+	if (info->file) {
+		fput(info->file);
+		info->file = NULL;
+	}
+	return task_vma_seq_get_next(info);
+}
+
+struct bpf_iter__task_vma {
+	__bpf_md_ptr(struct bpf_iter_meta *, meta);
+	__bpf_md_ptr(struct task_struct *, task);
+	__bpf_md_ptr(struct __vm_area_struct *, vma);
+	__bpf_md_ptr(struct file *, file);
+};
+
+DEFINE_BPF_ITER_FUNC(task_vma, struct bpf_iter_meta *meta,
+		     struct task_struct *task, struct __vm_area_struct *vma,
+		     struct file *file)
+
+static int __task_vma_seq_show(struct seq_file *seq, bool in_stop)
+{
+	struct bpf_iter_seq_task_vma_info *info = seq->private;
+	struct bpf_iter__task_vma ctx;
+	struct bpf_iter_meta meta;
+	struct bpf_prog *prog;
+
+	meta.seq = seq;
+	prog = bpf_iter_get_info(&meta, in_stop);
+	if (!prog)
+		return 0;
+
+	ctx.meta = &meta;
+	ctx.task = info->task;
+	ctx.vma = &info->vma;
+	ctx.file = info->file;
+	return bpf_iter_run_prog(prog, &ctx);
+}
+
+static int task_vma_seq_show(struct seq_file *seq, void *v)
+{
+	return __task_vma_seq_show(seq, false);
+}
+
+static void task_vma_seq_stop(struct seq_file *seq, void *v)
+{
+	struct bpf_iter_seq_task_vma_info *info = seq->private;
+
+	if (!v) {
+		(void)__task_vma_seq_show(seq, true);
+	} else {
+		put_task_struct(info->task);
+		if (info->file) {
+			fput(info->file);
+			info->file = NULL;
+		}
+	}
+}
+
+static const struct seq_operations task_vma_seq_ops = {
+	.start	= task_vma_seq_start,
+	.next	= task_vma_seq_next,
+	.stop	= task_vma_seq_stop,
+	.show	= task_vma_seq_show,
+};
+
 BTF_ID_LIST(btf_task_file_ids)
 BTF_ID(struct, task_struct)
 BTF_ID(struct, file)
+BTF_ID(struct, __vm_area_struct)
 
 static const struct bpf_iter_seq_info task_seq_info = {
 	.seq_ops		= &task_seq_ops,
@@ -346,6 +508,28 @@ static struct bpf_iter_reg task_file_reg_info = {
 	.seq_info		= &task_file_seq_info,
 };
 
+static const struct bpf_iter_seq_info task_vma_seq_info = {
+	.seq_ops		= &task_vma_seq_ops,
+	.init_seq_private	= init_seq_pidns,
+	.fini_seq_private	= fini_seq_pidns,
+	.seq_priv_size		= sizeof(struct bpf_iter_seq_task_vma_info),
+};
+
+static struct bpf_iter_reg task_vma_reg_info = {
+	.target			= "task_vma",
+	.feature		= BPF_ITER_RESCHED,
+	.ctx_arg_info_size	= 3,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__task_vma, task),
+		  PTR_TO_BTF_ID_OR_NULL },
+		{ offsetof(struct bpf_iter__task_vma, vma),
+		  PTR_TO_BTF_ID_OR_NULL },
+		{ offsetof(struct bpf_iter__task_vma, file),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
+	.seq_info		= &task_vma_seq_info,
+};
+
 static int __init task_iter_init(void)
 {
 	int ret;
@@ -357,6 +541,13 @@ static int __init task_iter_init(void)
 
 	task_file_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
 	task_file_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[1];
-	return bpf_iter_reg_target(&task_file_reg_info);
+	ret =  bpf_iter_reg_target(&task_file_reg_info);
+	if (ret)
+		return ret;
+
+	task_vma_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
+	task_vma_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[2];
+	task_vma_reg_info.ctx_arg_info[2].btf_id = btf_task_file_ids[1];
+	return bpf_iter_reg_target(&task_vma_reg_info);
 }
 late_initcall(task_iter_init);
-- 
2.24.1

[PATCH bpf-next 2/4] bpf: allow bpf_d_path in sleepable bpf_iter program

[Song Liu]

task_file and task_vma iter programs have access to file->f_path. Enable
bpf_d_path to print paths of these file.

bpf_iter programs are generally called in sleepable context. However, it
is still necessary to diffientiate sleepable and non-sleepable bpf_iter
programs: sleepable programs have access to bpf_d_path; non-sleepable
programs have access to bpf_spin_lock.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 kernel/trace/bpf_trace.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 52ddd217d6a19..839c654160d1b 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1191,6 +1191,11 @@ BTF_SET_END(btf_allowlist_d_path)
 
 static bool bpf_d_path_allowed(const struct bpf_prog *prog)
 {
+	if (prog->type == BPF_PROG_TYPE_TRACING &&
+	    prog->expected_attach_type == BPF_TRACE_ITER &&
+	    prog->aux->sleepable)
+		return true;
+
 	if (prog->type == BPF_PROG_TYPE_LSM)
 		return bpf_lsm_is_sleepable_hook(prog->aux->attach_btf_id);
 
-- 
2.24.1

[PATCH bpf-next 3/4] libbpf: introduce section "iter.s/" for sleepable bpf_iter program

[Song Liu]

Sleepable iterator program have access to helper functions like bpf_d_path.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 tools/lib/bpf/libbpf.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 9be88a90a4aad..9204d12d04bf8 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8535,6 +8535,11 @@ static const struct bpf_sec_def section_defs[] = {
 		.expected_attach_type = BPF_TRACE_ITER,
 		.is_attach_btf = true,
 		.attach_fn = attach_iter),
+	SEC_DEF("iter.s/", TRACING,
+		.expected_attach_type = BPF_TRACE_ITER,
+		.is_attach_btf = true,
+		.is_sleepable = true,
+		.attach_fn = attach_iter),
 	BPF_EAPROG_SEC("xdp_devmap/",		BPF_PROG_TYPE_XDP,
 						BPF_XDP_DEVMAP),
 	BPF_EAPROG_SEC("xdp_cpumap/",		BPF_PROG_TYPE_XDP,
-- 
2.24.1

[PATCH bpf-next 4/4] selftests/bpf: add test for bpf_iter_task_vma

[Song Liu]

The test dumps information similar to /proc/pid/maps. The first line of
the output is compared against the /proc file to make sure they match.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 .../selftests/bpf/prog_tests/bpf_iter.c       | 106 ++++++++++++++++--
 tools/testing/selftests/bpf/progs/bpf_iter.h  |   9 ++
 .../selftests/bpf/progs/bpf_iter_task_vma.c   |  55 +++++++++
 3 files changed, 160 insertions(+), 10 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index 0e586368948dd..7afd3abae1899 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -7,6 +7,7 @@
 #include "bpf_iter_task.skel.h"
 #include "bpf_iter_task_stack.skel.h"
 #include "bpf_iter_task_file.skel.h"
+#include "bpf_iter_task_vma.skel.h"
 #include "bpf_iter_task_btf.skel.h"
 #include "bpf_iter_tcp4.skel.h"
 #include "bpf_iter_tcp6.skel.h"
@@ -64,6 +65,22 @@ static void do_dummy_read(struct bpf_program *prog)
 	bpf_link__destroy(link);
 }
 
+static int read_fd_into_buffer(int fd, char *buf, int size)
+{
+	int bufleft = size;
+	int len;
+
+	do {
+		len = read(fd, buf, bufleft);
+		if (len > 0) {
+			buf += len;
+			bufleft -= len;
+		}
+	} while (len > 0);
+
+	return len;
+}
+
 static void test_ipv6_route(void)
 {
 	struct bpf_iter_ipv6_route *skel;
@@ -177,7 +194,7 @@ static int do_btf_read(struct bpf_iter_task_btf *skel)
 {
 	struct bpf_program *prog = skel->progs.dump_task_struct;
 	struct bpf_iter_task_btf__bss *bss = skel->bss;
-	int iter_fd = -1, len = 0, bufleft = TASKBUFSZ;
+	int iter_fd = -1, err;
 	struct bpf_link *link;
 	char *buf = taskbuf;
 	int ret = 0;
@@ -190,14 +207,7 @@ static int do_btf_read(struct bpf_iter_task_btf *skel)
 	if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
 		goto free_link;
 
-	do {
-		len = read(iter_fd, buf, bufleft);
-		if (len > 0) {
-			buf += len;
-			bufleft -= len;
-		}
-	} while (len > 0);
-
+	err = read_fd_into_buffer(iter_fd, buf, TASKBUFSZ);
 	if (bss->skip) {
 		printf("%s:SKIP:no __builtin_btf_type_id\n", __func__);
 		ret = 1;
@@ -205,7 +215,7 @@ static int do_btf_read(struct bpf_iter_task_btf *skel)
 		goto free_link;
 	}
 
-	if (CHECK(len < 0, "read", "read failed: %s\n", strerror(errno)))
+	if (CHECK(err < 0, "read", "read failed: %s\n", strerror(errno)))
 		goto free_link;
 
 	CHECK(strstr(taskbuf, "(struct task_struct)") == NULL,
@@ -1133,6 +1143,80 @@ static void test_buf_neg_offset(void)
 		bpf_iter_test_kern6__destroy(skel);
 }
 
+#define CMP_BUFFER_SIZE 1024
+char task_vma_output[CMP_BUFFER_SIZE];
+char proc_maps_output[CMP_BUFFER_SIZE];
+
+/* remove \0 and \t from str, and only keep the first line */
+static void str_strip_first_line(char *str)
+{
+	char *dst = str, *src = str;
+
+	do {
+		if (*src == ' ' || *src == '\t')
+			src++;
+		else
+			*(dst++) = *(src++);
+
+	} while (*src != '\0' && *src != '\n');
+
+	*dst = '\0';
+}
+
+static void test_task_vma(void)
+{
+	int err, iter_fd = -1, proc_maps_fd = -1;
+	struct bpf_iter_task_vma *skel;
+	char maps_path[64];
+
+	skel = bpf_iter_task_vma__open();
+	if (CHECK(!skel, "bpf_iter_task_vma__open", "skeleton open failed\n"))
+		return;
+
+	skel->bss->pid = getpid();
+
+	err = bpf_iter_task_vma__load(skel);
+	if (CHECK(err, "bpf_iter_task_vma__load", "skeleton load failed\n"))
+		goto out;
+
+	do_dummy_read(skel->progs.proc_maps);
+
+	skel->links.proc_maps = bpf_program__attach_iter(
+		skel->progs.proc_maps, NULL);
+
+	if (CHECK(IS_ERR(skel->links.proc_maps), "bpf_program__attach_iter",
+		  "attach iterator failed\n"))
+		goto out;
+
+	/* read 1kB from bpf_iter */
+	iter_fd = bpf_iter_create(bpf_link__fd(skel->links.proc_maps));
+	if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
+		goto out;
+	err = read_fd_into_buffer(iter_fd, task_vma_output, CMP_BUFFER_SIZE);
+	if (CHECK(err < 0, "read_iter_fd", "read_iter_fd failed\n"))
+		goto out;
+
+	/* read 1kB from /proc/pid/maps */
+	snprintf(maps_path, 64, "/proc/%u/maps", skel->bss->pid);
+	proc_maps_fd = open(maps_path, O_RDONLY);
+	if (CHECK(proc_maps_fd < 0, "open_proc_maps", "open_proc_maps failed\n"))
+		goto out;
+	err = read_fd_into_buffer(proc_maps_fd, proc_maps_output, CMP_BUFFER_SIZE);
+	if (CHECK(err < 0, "read_prog_maps_fd", "read_prog_maps_fd failed\n"))
+		goto out;
+
+	/* strip and compare the first line of the two files */
+	str_strip_first_line(task_vma_output);
+	str_strip_first_line(proc_maps_output);
+
+	CHECK(strcmp(task_vma_output, proc_maps_output), "compare_output",
+	      "found mismatch\n");
+out:
+	close(proc_maps_fd);
+	close(iter_fd);
+	bpf_iter_task_vma__destroy(skel);
+}
+
 void test_bpf_iter(void)
 {
 	if (test__start_subtest("btf_id_or_null"))
@@ -1149,6 +1233,8 @@ void test_bpf_iter(void)
 		test_task_stack();
 	if (test__start_subtest("task_file"))
 		test_task_file();
+	if (test__start_subtest("task_vma"))
+		test_task_vma();
 	if (test__start_subtest("task_btf"))
 		test_task_btf();
 	if (test__start_subtest("tcp4"))
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter.h b/tools/testing/selftests/bpf/progs/bpf_iter.h
index 6a1255465fd6d..4dab0869c4fcb 100644
--- a/tools/testing/selftests/bpf/progs/bpf_iter.h
+++ b/tools/testing/selftests/bpf/progs/bpf_iter.h
@@ -7,6 +7,7 @@
 #define bpf_iter__netlink bpf_iter__netlink___not_used
 #define bpf_iter__task bpf_iter__task___not_used
 #define bpf_iter__task_file bpf_iter__task_file___not_used
+#define bpf_iter__task_vma bpf_iter__task_vma___not_used
 #define bpf_iter__tcp bpf_iter__tcp___not_used
 #define tcp6_sock tcp6_sock___not_used
 #define bpf_iter__udp bpf_iter__udp___not_used
@@ -26,6 +27,7 @@
 #undef bpf_iter__netlink
 #undef bpf_iter__task
 #undef bpf_iter__task_file
+#undef bpf_iter__task_vma
 #undef bpf_iter__tcp
 #undef tcp6_sock
 #undef bpf_iter__udp
@@ -67,6 +69,13 @@ struct bpf_iter__task_file {
 	struct file *file;
 } __attribute__((preserve_access_index));
 
+struct bpf_iter__task_vma {
+	struct bpf_iter_meta *meta;
+	struct task_struct *task;
+	struct __vm_area_struct *vma;
+	struct file *file;
+} __attribute__((preserve_access_index));
+
 struct bpf_iter__bpf_map {
 	struct bpf_iter_meta *meta;
 	struct bpf_map *map;
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
new file mode 100644
index 0000000000000..d60b5b38cb396
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "bpf_iter.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+/* Copied from mm.h */
+#define VM_READ		0x00000001
+#define VM_WRITE	0x00000002
+#define VM_EXEC		0x00000004
+#define VM_MAYSHARE	0x00000080
+
+/* Copied from kdev_t.h */
+#define MINORBITS	20
+#define MINORMASK	((1U << MINORBITS) - 1)
+#define MAJOR(dev)	((unsigned int) ((dev) >> MINORBITS))
+#define MINOR(dev)	((unsigned int) ((dev) & MINORMASK))
+
+#define D_PATH_BUF_SIZE 1024
+char d_path_buf[D_PATH_BUF_SIZE];
+__u32 pid;
+
+SEC("iter.s/task_vma") int proc_maps(struct bpf_iter__task_vma *ctx)
+{
+	struct __vm_area_struct *vma = ctx->vma;
+	struct seq_file *seq = ctx->meta->seq;
+	struct task_struct *task = ctx->task;
+	struct file *file = ctx->file;
+	char perm_str[] = "----";
+
+	if (task == (void *)0 || vma == (void *)0 || task->pid != pid)
+		return 0;
+
+	perm_str[0] = (vma->flags & VM_READ) ? 'r' : '-';
+	perm_str[1] = (vma->flags & VM_WRITE) ? 'w' : '-';
+	perm_str[1] = (vma->flags & VM_EXEC) ? 'x' : '-';
+	perm_str[3] = (vma->flags & VM_MAYSHARE) ? 's' : 'p';
+	BPF_SEQ_PRINTF(seq, "%08llx-%08llx %s ", vma->start, vma->end, perm_str);
+
+	if (file) {
+		__u32 dev = file->f_inode->i_sb->s_dev;
+
+		bpf_d_path(&file->f_path, d_path_buf, D_PATH_BUF_SIZE);
+
+		BPF_SEQ_PRINTF(seq, "%08llx ", vma->pgoff << 12);
+		BPF_SEQ_PRINTF(seq, "%02x:%02x %u", MAJOR(dev), MINOR(dev),
+			       file->f_inode->i_ino);
+		BPF_SEQ_PRINTF(seq, "\t%s\n", d_path_buf);
+	} else {
+		BPF_SEQ_PRINTF(seq, "%08llx 00:00 0\n", 0ULL);
+	}
+	return 0;
+}
-- 
2.24.1

Re: [PATCH bpf-next 1/4] bpf: introduce task_vma bpf_iter

[Yonghong Song]

On 12/11/20 6:48 PM, Song Liu wrote:
> Introduce task_vma bpf_iter to print memory information of a process. It
> can be used to print customized information similar to /proc/<pid>/maps.
> 
> task_vma iterator releases mmap_lock before calling the BPF program.
> Therefore, we cannot pass vm_area_struct directly to the BPF program. A
> new __vm_area_struct is introduced to keep key information of a vma. On
> each iteration, task_vma gathers information in __vm_area_struct and
> passes it to the BPF program.
> 
> If the vma maps to a file, task_vma also holds a reference to the file
> while calling the BPF program.
> 
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>   include/linux/bpf.h      |   2 +-
>   include/uapi/linux/bpf.h |   7 ++
>   kernel/bpf/task_iter.c   | 193 ++++++++++++++++++++++++++++++++++++++-
>   3 files changed, 200 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 07cb5d15e7439..49dd1e29c8118 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1325,7 +1325,7 @@ enum bpf_iter_feature {
>   	BPF_ITER_RESCHED	= BIT(0),
>   };
>   
> -#define BPF_ITER_CTX_ARG_MAX 2
> +#define BPF_ITER_CTX_ARG_MAX 3
>   struct bpf_iter_reg {
>   	const char *target;
>   	bpf_iter_attach_target_t attach_target;
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 30b477a264827..c2db8a1d0cbd2 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5151,4 +5151,11 @@ enum {
>   	BTF_F_ZERO	=	(1ULL << 3),
>   };
>   
> +struct __vm_area_struct {
> +	__u64 start;
> +	__u64 end;
> +	__u64 flags;
> +	__u64 pgoff;
> +};

Probably we should not expose the above structure as uapi.
All other bpf_iter ctx argument layouts are btf based
and consider unstable. btf_iter itself is considered
as an unstable interface to dump kernel internal
data structures.

> +
>   #endif /* _UAPI__LINUX_BPF_H__ */
> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> index 0458a40edf10a..30e5475d0831e 100644
> --- a/kernel/bpf/task_iter.c
> +++ b/kernel/bpf/task_iter.c
> @@ -304,9 +304,171 @@ static const struct seq_operations task_file_seq_ops = {
>   	.show	= task_file_seq_show,
>   };
>   
> +struct bpf_iter_seq_task_vma_info {
> +	/* The first field must be struct bpf_iter_seq_task_common.
> +	 * this is assumed by {init, fini}_seq_pidns() callback functions.
> +	 */
> +	struct bpf_iter_seq_task_common common;
> +	struct task_struct *task;
> +	struct __vm_area_struct vma;
> +	struct file *file;
> +	u32 tid;
> +};
> +
[...]

Re: [PATCH bpf-next 1/4] bpf: introduce task_vma bpf_iter

[Song Liu]

> On Dec 13, 2020, at 11:13 PM, Yonghong Song <yhs@fb.com> wrote:
> 
> 
> 
> On 12/11/20 6:48 PM, Song Liu wrote:
>> Introduce task_vma bpf_iter to print memory information of a process. It
>> can be used to print customized information similar to /proc/<pid>/maps.
>> task_vma iterator releases mmap_lock before calling the BPF program.
>> Therefore, we cannot pass vm_area_struct directly to the BPF program. A
>> new __vm_area_struct is introduced to keep key information of a vma. On
>> each iteration, task_vma gathers information in __vm_area_struct and
>> passes it to the BPF program.
>> If the vma maps to a file, task_vma also holds a reference to the file
>> while calling the BPF program.
>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> ---
>>  include/linux/bpf.h      |   2 +-
>>  include/uapi/linux/bpf.h |   7 ++
>>  kernel/bpf/task_iter.c   | 193 ++++++++++++++++++++++++++++++++++++++-
>>  3 files changed, 200 insertions(+), 2 deletions(-)
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index 07cb5d15e7439..49dd1e29c8118 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -1325,7 +1325,7 @@ enum bpf_iter_feature {
>>  	BPF_ITER_RESCHED	= BIT(0),
>>  };
>>  -#define BPF_ITER_CTX_ARG_MAX 2
>> +#define BPF_ITER_CTX_ARG_MAX 3
>>  struct bpf_iter_reg {
>>  	const char *target;
>>  	bpf_iter_attach_target_t attach_target;
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 30b477a264827..c2db8a1d0cbd2 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -5151,4 +5151,11 @@ enum {
>>  	BTF_F_ZERO	=	(1ULL << 3),
>>  };
>>  +struct __vm_area_struct {
>> +	__u64 start;
>> +	__u64 end;
>> +	__u64 flags;
>> +	__u64 pgoff;
>> +};
> 
> Probably we should not expose the above structure as uapi.
> All other bpf_iter ctx argument layouts are btf based
> and consider unstable. btf_iter itself is considered
> as an unstable interface to dump kernel internal
> data structures.

Yes, we can keep it in task_iter.c. I moved it to uapi to follow __sk_buff
pattern. It works fine in task_iter.c

Thanks,
Song



> 
>> +
>>  #endif /* _UAPI__LINUX_BPF_H__ */
>> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
>> index 0458a40edf10a..30e5475d0831e 100644
>> --- a/kernel/bpf/task_iter.c
>> +++ b/kernel/bpf/task_iter.c
>> @@ -304,9 +304,171 @@ static const struct seq_operations task_file_seq_ops = {
>>  	.show	= task_file_seq_show,
>>  };
>>  +struct bpf_iter_seq_task_vma_info {
>> +	/* The first field must be struct bpf_iter_seq_task_common.
>> +	 * this is assumed by {init, fini}_seq_pidns() callback functions.
>> +	 */
>> +	struct bpf_iter_seq_task_common common;
>> +	struct task_struct *task;
>> +	struct __vm_area_struct vma;
>> +	struct file *file;
>> +	u32 tid;
>> +};
>> +
> [...]

Re: [PATCH bpf-next 1/4] bpf: introduce task_vma bpf_iter

[Yonghong Song]

On 12/11/20 6:48 PM, Song Liu wrote:
> Introduce task_vma bpf_iter to print memory information of a process. It
> can be used to print customized information similar to /proc/<pid>/maps.
> 
> task_vma iterator releases mmap_lock before calling the BPF program.
> Therefore, we cannot pass vm_area_struct directly to the BPF program. A
> new __vm_area_struct is introduced to keep key information of a vma. On
> each iteration, task_vma gathers information in __vm_area_struct and
> passes it to the BPF program.
> 
> If the vma maps to a file, task_vma also holds a reference to the file
> while calling the BPF program.
> 
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>   include/linux/bpf.h      |   2 +-
>   include/uapi/linux/bpf.h |   7 ++
>   kernel/bpf/task_iter.c   | 193 ++++++++++++++++++++++++++++++++++++++-
>   3 files changed, 200 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 07cb5d15e7439..49dd1e29c8118 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1325,7 +1325,7 @@ enum bpf_iter_feature {
>   	BPF_ITER_RESCHED	= BIT(0),
>   };
>   
> -#define BPF_ITER_CTX_ARG_MAX 2
> +#define BPF_ITER_CTX_ARG_MAX 3
>   struct bpf_iter_reg {
>   	const char *target;
>   	bpf_iter_attach_target_t attach_target;
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 30b477a264827..c2db8a1d0cbd2 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5151,4 +5151,11 @@ enum {
>   	BTF_F_ZERO	=	(1ULL << 3),
>   };
>   
> +struct __vm_area_struct {
> +	__u64 start;
> +	__u64 end;
> +	__u64 flags;
> +	__u64 pgoff;
> +};
> +
>   #endif /* _UAPI__LINUX_BPF_H__ */
> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> index 0458a40edf10a..30e5475d0831e 100644
> --- a/kernel/bpf/task_iter.c
> +++ b/kernel/bpf/task_iter.c
> @@ -304,9 +304,171 @@ static const struct seq_operations task_file_seq_ops = {
>   	.show	= task_file_seq_show,
>   };
>   
> +struct bpf_iter_seq_task_vma_info {
> +	/* The first field must be struct bpf_iter_seq_task_common.
> +	 * this is assumed by {init, fini}_seq_pidns() callback functions.
> +	 */
> +	struct bpf_iter_seq_task_common common;
> +	struct task_struct *task;
> +	struct __vm_area_struct vma;
> +	struct file *file;
> +	u32 tid;
> +};
> +
> +static struct __vm_area_struct *
> +task_vma_seq_get_next(struct bpf_iter_seq_task_vma_info *info)
> +{
> +	struct pid_namespace *ns = info->common.ns;
> +	struct task_struct *curr_task;
> +	struct vm_area_struct *vma;
> +	u32 curr_tid = info->tid;
> +	bool new_task = false;
> +
> +	/* If this function returns a non-NULL vma, it held a reference to

the function does not return vma, it returns an internal data
structure __vm_area_struct which captures some fields from vma.

> +	 * the task_struct. If info->file is non-NULL, it also holds a
> +	 * reference to the file. Otherwise, it does not hold any
> +	 * reference.
> +	 */
> +again:
> +	if (info->task) {
> +		curr_task = info->task;
> +	} else {
> +		curr_task = task_seq_get_next(ns, &curr_tid, true);
> +		if (!curr_task) {
> +			info->task = NULL;

adding "info->tid = curr_tid  + 1" so next read, e.g. after read()
syscall return 0 read length, will start after last checked curr_tid.

> +			return NULL;
> +		}
> +
> +		if (curr_tid != info->tid) {
> +			info->tid = curr_tid;
> +			new_task = true;
> +		}
> +
> +		if (!curr_task->mm)
> +			goto next_task;
> +		info->task = curr_task;
> +	}
> +
> +	mmap_read_lock(curr_task->mm);
> +	if (new_task) {
> +		vma = curr_task->mm->mmap;
> +	} else {
> +		/* We drop the lock between each iteration, so it is
> +		 * necessary to use find_vma() to find the next vma. This
> +		 * is similar to the mechanism in show_smaps_rollup().
> +		 */
> +		vma = find_vma(curr_task->mm, info->vma.end - 1);
> +		/* same vma as previous iteration, use vma->next */
> +		if (vma && (vma->vm_start == info->vma.start))
> +			vma = vma->vm_next;
> +	}
> +	if (!vma) {
> +		mmap_read_unlock(curr_task->mm);
> +		goto next_task;
> +	}
> +	info->task = curr_task;
> +	info->vma.start = vma->vm_start;
> +	info->vma.end = vma->vm_end;
> +	info->vma.pgoff = vma->vm_pgoff;
> +	info->vma.flags = vma->vm_flags;
> +	if (vma->vm_file)
> +		info->file = get_file(vma->vm_file);
> +	mmap_read_unlock(curr_task->mm);
> +	return &info->vma;
> +
> +next_task:
> +	put_task_struct(curr_task);
> +	info->task = NULL;
> +	curr_tid = ++(info->tid);
> +	goto again;
> +}
> +
> +static void *task_vma_seq_start(struct seq_file *seq, loff_t *pos)
> +{
> +	struct bpf_iter_seq_task_vma_info *info = seq->private;
> +	struct __vm_area_struct *vma;
> +
> +	info->task = NULL;

Maybe put info->task = NULL in task_vma_seq_stop()?

> +	vma = task_vma_seq_get_next(info);
> +	if (vma && *pos == 0)
> +		++*pos;
> +
> +	return vma;
> +}
> +
> +static void *task_vma_seq_next(struct seq_file *seq, void *v, loff_t *pos)
> +{
> +	struct bpf_iter_seq_task_vma_info *info = seq->private;
> +
> +	++*pos;
> +	if (info->file) {
> +		fput(info->file);
> +		info->file = NULL;
> +	}
> +	return task_vma_seq_get_next(info);
> +}
> +
> +struct bpf_iter__task_vma {
> +	__bpf_md_ptr(struct bpf_iter_meta *, meta);
> +	__bpf_md_ptr(struct task_struct *, task);
> +	__bpf_md_ptr(struct __vm_area_struct *, vma);
> +	__bpf_md_ptr(struct file *, file);
> +};
> +
> +DEFINE_BPF_ITER_FUNC(task_vma, struct bpf_iter_meta *meta,
> +		     struct task_struct *task, struct __vm_area_struct *vma,
> +		     struct file *file)
> +
[...]

Re: [PATCH bpf-next 4/4] selftests/bpf: add test for bpf_iter_task_vma

[Yonghong Song]

On 12/11/20 6:48 PM, Song Liu wrote:
> The test dumps information similar to /proc/pid/maps. The first line of
> the output is compared against the /proc file to make sure they match.
> 
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>   .../selftests/bpf/prog_tests/bpf_iter.c       | 106 ++++++++++++++++--
>   tools/testing/selftests/bpf/progs/bpf_iter.h  |   9 ++
>   .../selftests/bpf/progs/bpf_iter_task_vma.c   |  55 +++++++++
>   3 files changed, 160 insertions(+), 10 deletions(-)
>   create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> index 0e586368948dd..7afd3abae1899 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> @@ -7,6 +7,7 @@
>   #include "bpf_iter_task.skel.h"
>   #include "bpf_iter_task_stack.skel.h"
>   #include "bpf_iter_task_file.skel.h"
> +#include "bpf_iter_task_vma.skel.h"
>   #include "bpf_iter_task_btf.skel.h"
>   #include "bpf_iter_tcp4.skel.h"
>   #include "bpf_iter_tcp6.skel.h"
> @@ -64,6 +65,22 @@ static void do_dummy_read(struct bpf_program *prog)
>   	bpf_link__destroy(link);
>   }
>   
[...]
> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
> new file mode 100644
> index 0000000000000..d60b5b38cb396
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
> @@ -0,0 +1,55 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2020 Facebook */
> +#include "bpf_iter.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +/* Copied from mm.h */
> +#define VM_READ		0x00000001
> +#define VM_WRITE	0x00000002
> +#define VM_EXEC		0x00000004
> +#define VM_MAYSHARE	0x00000080
> +
> +/* Copied from kdev_t.h */
> +#define MINORBITS	20
> +#define MINORMASK	((1U << MINORBITS) - 1)
> +#define MAJOR(dev)	((unsigned int) ((dev) >> MINORBITS))
> +#define MINOR(dev)	((unsigned int) ((dev) & MINORMASK))
> +
> +#define D_PATH_BUF_SIZE 1024
> +char d_path_buf[D_PATH_BUF_SIZE];
> +__u32 pid;
> +
> +SEC("iter.s/task_vma") int proc_maps(struct bpf_iter__task_vma *ctx)
> +{
> +	struct __vm_area_struct *vma = ctx->vma;
> +	struct seq_file *seq = ctx->meta->seq;
> +	struct task_struct *task = ctx->task;
> +	struct file *file = ctx->file;
> +	char perm_str[] = "----";
> +
> +	if (task == (void *)0 || vma == (void *)0 || task->pid != pid)
> +		return 0;
> +
> +	perm_str[0] = (vma->flags & VM_READ) ? 'r' : '-';
> +	perm_str[1] = (vma->flags & VM_WRITE) ? 'w' : '-';
> +	perm_str[1] = (vma->flags & VM_EXEC) ? 'x' : '-';

typo here? The above should be perm_str[2].

> +	perm_str[3] = (vma->flags & VM_MAYSHARE) ? 's' : 'p';
> +	BPF_SEQ_PRINTF(seq, "%08llx-%08llx %s ", vma->start, vma->end, perm_str);
> +
> +	if (file) {
> +		__u32 dev = file->f_inode->i_sb->s_dev;
> +
> +		bpf_d_path(&file->f_path, d_path_buf, D_PATH_BUF_SIZE);
> +
> +		BPF_SEQ_PRINTF(seq, "%08llx ", vma->pgoff << 12);
> +		BPF_SEQ_PRINTF(seq, "%02x:%02x %u", MAJOR(dev), MINOR(dev),
> +			       file->f_inode->i_ino);
> +		BPF_SEQ_PRINTF(seq, "\t%s\n", d_path_buf);
> +	} else {
> +		BPF_SEQ_PRINTF(seq, "%08llx 00:00 0\n", 0ULL);
> +	}
> +	return 0;
> +}
> 

Re: [PATCH bpf-next 4/4] selftests/bpf: add test for bpf_iter_task_vma

[Song Liu]

> On Dec 15, 2020, at 12:21 PM, Yonghong Song <yhs@fb.com> wrote:
> 
> 
> 
> On 12/11/20 6:48 PM, Song Liu wrote:
>> The test dumps information similar to /proc/pid/maps. The first line of
>> the output is compared against the /proc file to make sure they match.
>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> ---
>>  .../selftests/bpf/prog_tests/bpf_iter.c       | 106 ++++++++++++++++--
>>  tools/testing/selftests/bpf/progs/bpf_iter.h  |   9 ++
>>  .../selftests/bpf/progs/bpf_iter_task_vma.c   |  55 +++++++++
>>  3 files changed, 160 insertions(+), 10 deletions(-)
>>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
>> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
>> index 0e586368948dd..7afd3abae1899 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
>> @@ -7,6 +7,7 @@
>>  #include "bpf_iter_task.skel.h"
>>  #include "bpf_iter_task_stack.skel.h"
>>  #include "bpf_iter_task_file.skel.h"
>> +#include "bpf_iter_task_vma.skel.h"
>>  #include "bpf_iter_task_btf.skel.h"
>>  #include "bpf_iter_tcp4.skel.h"
>>  #include "bpf_iter_tcp6.skel.h"
>> @@ -64,6 +65,22 @@ static void do_dummy_read(struct bpf_program *prog)
>>  	bpf_link__destroy(link);
>>  }
>>  
> [...]
>> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
>> new file mode 100644
>> index 0000000000000..d60b5b38cb396
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
>> @@ -0,0 +1,55 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2020 Facebook */
>> +#include "bpf_iter.h"
>> +#include <bpf/bpf_helpers.h>
>> +#include <bpf/bpf_tracing.h>
>> +
>> +char _license[] SEC("license") = "GPL";
>> +
>> +/* Copied from mm.h */
>> +#define VM_READ		0x00000001
>> +#define VM_WRITE	0x00000002
>> +#define VM_EXEC		0x00000004
>> +#define VM_MAYSHARE	0x00000080
>> +
>> +/* Copied from kdev_t.h */
>> +#define MINORBITS	20
>> +#define MINORMASK	((1U << MINORBITS) - 1)
>> +#define MAJOR(dev)	((unsigned int) ((dev) >> MINORBITS))
>> +#define MINOR(dev)	((unsigned int) ((dev) & MINORMASK))
>> +
>> +#define D_PATH_BUF_SIZE 1024
>> +char d_path_buf[D_PATH_BUF_SIZE];
>> +__u32 pid;
>> +
>> +SEC("iter.s/task_vma") int proc_maps(struct bpf_iter__task_vma *ctx)
>> +{
>> +	struct __vm_area_struct *vma = ctx->vma;
>> +	struct seq_file *seq = ctx->meta->seq;
>> +	struct task_struct *task = ctx->task;
>> +	struct file *file = ctx->file;
>> +	char perm_str[] = "----";
>> +
>> +	if (task == (void *)0 || vma == (void *)0 || task->pid != pid)
>> +		return 0;
>> +
>> +	perm_str[0] = (vma->flags & VM_READ) ? 'r' : '-';
>> +	perm_str[1] = (vma->flags & VM_WRITE) ? 'w' : '-';
>> +	perm_str[1] = (vma->flags & VM_EXEC) ? 'x' : '-';
> 
> typo here? The above should be perm_str[2].

Good catch! Fixing it in the next version.

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