[PATCH v4 bpf-next 2/3] bpf: Introduce task_vma open-coded iterator kfuncs

[Dave Marchevsky <davemarchevsky@fb.com>]

This patch adds kfuncs bpf_iter_task_vma_{new,next,destroy} which allow
creation and manipulation of struct bpf_iter_task_vma in open-coded
iterator style. BPF programs can use these kfuncs directly or through
bpf_for_each macro for natural-looking iteration of all task vmas.

The implementation borrows heavily from bpf_find_vma helper's locking -
differing only in that it holds the mmap_read lock for all iterations
while the helper only executes its provided callback on a maximum of 1
vma. Aside from locking, struct vma_iterator and vma_next do all the
heavy lifting.

The newly-added struct bpf_iter_task_vma has a name collision with a
selftest for the seq_file task_vma iter's bpf skel, so the selftests/bpf/progs
file is renamed in order to avoid the collision.

A pointer to an inner data struct, struct bpf_iter_task_vma_data, is the
only field in struct bpf_iter_task_vma. This is because the inner data
struct contains a struct vma_iterator (not ptr), whose size is likely to
change under us. If bpf_iter_task_vma_kern contained vma_iterator directly
such a change would require change in opaque bpf_iter_task_vma struct's
size. So better to allocate vma_iterator using BPF allocator, and since
that alloc must already succeed, might as well allocate all iter fields,
thereby freezing struct bpf_iter_task_vma size.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Cc: Nathan Slingerland <slinger@meta.com>
---
 kernel/bpf/helpers.c                          |  3 +
 kernel/bpf/task_iter.c                        | 85 +++++++++++++++++++
 tools/lib/bpf/bpf_helpers.h                   |  8 ++
 .../selftests/bpf/prog_tests/bpf_iter.c       | 26 +++---
 ...f_iter_task_vma.c => bpf_iter_task_vmas.c} |  0
 5 files changed, 109 insertions(+), 13 deletions(-)
 rename tools/testing/selftests/bpf/progs/{bpf_iter_task_vma.c => bpf_iter_task_vmas.c} (100%)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index dd1c69ee3375..6b2373db65bd 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2549,6 +2549,9 @@ BTF_ID_FLAGS(func, bpf_dynptr_slice_rdwr, KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_num_new, KF_ITER_NEW)
 BTF_ID_FLAGS(func, bpf_iter_num_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_num_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_iter_task_vma_new, KF_ITER_NEW | KF_RCU)
+BTF_ID_FLAGS(func, bpf_iter_task_vma_next, KF_ITER_NEXT | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_task_vma_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_dynptr_adjust)
 BTF_ID_FLAGS(func, bpf_dynptr_is_null)
 BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 7473068ed313..5c8e559be5e5 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -7,7 +7,9 @@
 #include <linux/fs.h>
 #include <linux/fdtable.h>
 #include <linux/filter.h>
+#include <linux/bpf_mem_alloc.h>
 #include <linux/btf_ids.h>
+#include <linux/mm_types.h>
 #include "mmap_unlock_work.h"
 
 static const char * const iter_task_type_names[] = {
@@ -803,6 +805,89 @@ const struct bpf_func_proto bpf_find_vma_proto = {
 	.arg5_type	= ARG_ANYTHING,
 };
 
+struct bpf_iter_task_vma_kern_data {
+	struct task_struct *task;
+	struct mm_struct *mm;
+	struct mmap_unlock_irq_work *work;
+	struct vma_iterator vmi;
+};
+
+struct bpf_iter_task_vma {
+	/* opaque iterator state; having __u64 here allows to preserve correct
+	 * alignment requirements in vmlinux.h, generated from BTF
+	 */
+	__u64 __opaque[1];
+} __attribute__((aligned(8)));
+
+/* Non-opaque version of bpf_iter_task_vma */
+struct bpf_iter_task_vma_kern {
+	struct bpf_iter_task_vma_kern_data *data;
+} __attribute__((aligned(8)));
+
+__bpf_kfunc int bpf_iter_task_vma_new(struct bpf_iter_task_vma *it,
+				      struct task_struct *task, u64 addr)
+{
+	struct bpf_iter_task_vma_kern *kit = (void *)it;
+	bool irq_work_busy = false;
+	int err;
+
+	BUILD_BUG_ON(sizeof(struct bpf_iter_task_vma_kern) != sizeof(struct bpf_iter_task_vma));
+	BUILD_BUG_ON(__alignof__(struct bpf_iter_task_vma_kern) != __alignof__(struct bpf_iter_task_vma));
+
+	/* is_iter_reg_valid_uninit guarantees that kit hasn't been initialized
+	 * before, so non-NULL kit->data doesn't point to previously
+	 * bpf_mem_alloc'd bpf_iter_task_vma_kern_data
+	 */
+	kit->data = bpf_mem_alloc(&bpf_global_ma, sizeof(struct bpf_iter_task_vma_kern_data));
+	if (!kit->data)
+		return -ENOMEM;
+
+	kit->data->task = get_task_struct(task);
+	kit->data->mm = task->mm;
+	if (!kit->data->mm) {
+		err = -ENOENT;
+		goto err_cleanup_iter;
+	}
+
+	/* kit->data->work == NULL is valid after bpf_mmap_unlock_get_irq_work */
+	irq_work_busy = bpf_mmap_unlock_get_irq_work(&kit->data->work);
+	if (irq_work_busy || !mmap_read_trylock(kit->data->mm)) {
+		err = -EBUSY;
+		goto err_cleanup_iter;
+	}
+
+	vma_iter_init(&kit->data->vmi, kit->data->mm, addr);
+	return 0;
+
+err_cleanup_iter:
+	if (kit->data->task)
+		put_task_struct(kit->data->task);
+	bpf_mem_free(&bpf_global_ma, kit->data);
+	/* NULL kit->data signals failed bpf_iter_task_vma initialization */
+	kit->data = NULL;
+	return err;
+}
+
+__bpf_kfunc struct vm_area_struct *bpf_iter_task_vma_next(struct bpf_iter_task_vma *it)
+{
+	struct bpf_iter_task_vma_kern *kit = (void *)it;
+
+	if (!kit->data) /* bpf_iter_task_vma_new failed */
+		return NULL;
+	return vma_next(&kit->data->vmi);
+}
+
+__bpf_kfunc void bpf_iter_task_vma_destroy(struct bpf_iter_task_vma *it)
+{
+	struct bpf_iter_task_vma_kern *kit = (void *)it;
+
+	if (kit->data) {
+		bpf_mmap_unlock_mm(kit->data->work, kit->data->mm);
+		put_task_struct(kit->data->task);
+		bpf_mem_free(&bpf_global_ma, kit->data);
+	}
+}
+
 DEFINE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work);
 
 static void do_mmap_read_unlock(struct irq_work *entry)
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index 77ceea575dc7..c6abb7fd8d73 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -303,6 +303,14 @@ extern int bpf_iter_num_new(struct bpf_iter_num *it, int start, int end) __weak
 extern int *bpf_iter_num_next(struct bpf_iter_num *it) __weak __ksym;
 extern void bpf_iter_num_destroy(struct bpf_iter_num *it) __weak __ksym;
 
+struct bpf_iter_task_vma;
+
+extern int bpf_iter_task_vma_new(struct bpf_iter_task_vma *it,
+				 struct task_struct *task,
+				 unsigned long addr) __weak __ksym;
+extern struct vm_area_struct *bpf_iter_task_vma_next(struct bpf_iter_task_vma *it) __weak __ksym;
+extern void bpf_iter_task_vma_destroy(struct bpf_iter_task_vma *it) __weak __ksym;
+
 #ifndef bpf_for_each
 /* bpf_for_each(iter_type, cur_elem, args...) provides generic construct for
  * using BPF open-coded iterators without having to write mundane explicit
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index 1f02168103dd..41aba139b20b 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -10,7 +10,7 @@
 #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_vmas.skel.h"
 #include "bpf_iter_task_btf.skel.h"
 #include "bpf_iter_tcp4.skel.h"
 #include "bpf_iter_tcp6.skel.h"
@@ -1399,19 +1399,19 @@ static void str_strip_first_line(char *str)
 static void test_task_vma_common(struct bpf_iter_attach_opts *opts)
 {
 	int err, iter_fd = -1, proc_maps_fd = -1;
-	struct bpf_iter_task_vma *skel;
+	struct bpf_iter_task_vmas *skel;
 	int len, read_size = 4;
 	char maps_path[64];
 
-	skel = bpf_iter_task_vma__open();
-	if (!ASSERT_OK_PTR(skel, "bpf_iter_task_vma__open"))
+	skel = bpf_iter_task_vmas__open();
+	if (!ASSERT_OK_PTR(skel, "bpf_iter_task_vmas__open"))
 		return;
 
 	skel->bss->pid = getpid();
 	skel->bss->one_task = opts ? 1 : 0;
 
-	err = bpf_iter_task_vma__load(skel);
-	if (!ASSERT_OK(err, "bpf_iter_task_vma__load"))
+	err = bpf_iter_task_vmas__load(skel);
+	if (!ASSERT_OK(err, "bpf_iter_task_vmas__load"))
 		goto out;
 
 	skel->links.proc_maps = bpf_program__attach_iter(
@@ -1462,25 +1462,25 @@ static void test_task_vma_common(struct bpf_iter_attach_opts *opts)
 out:
 	close(proc_maps_fd);
 	close(iter_fd);
-	bpf_iter_task_vma__destroy(skel);
+	bpf_iter_task_vmas__destroy(skel);
 }
 
 static void test_task_vma_dead_task(void)
 {
-	struct bpf_iter_task_vma *skel;
+	struct bpf_iter_task_vmas *skel;
 	int wstatus, child_pid = -1;
 	time_t start_tm, cur_tm;
 	int err, iter_fd = -1;
 	int wait_sec = 3;
 
-	skel = bpf_iter_task_vma__open();
-	if (!ASSERT_OK_PTR(skel, "bpf_iter_task_vma__open"))
+	skel = bpf_iter_task_vmas__open();
+	if (!ASSERT_OK_PTR(skel, "bpf_iter_task_vmas__open"))
 		return;
 
 	skel->bss->pid = getpid();
 
-	err = bpf_iter_task_vma__load(skel);
-	if (!ASSERT_OK(err, "bpf_iter_task_vma__load"))
+	err = bpf_iter_task_vmas__load(skel);
+	if (!ASSERT_OK(err, "bpf_iter_task_vmas__load"))
 		goto out;
 
 	skel->links.proc_maps = bpf_program__attach_iter(
@@ -1533,7 +1533,7 @@ static void test_task_vma_dead_task(void)
 out:
 	waitpid(child_pid, &wstatus, 0);
 	close(iter_fd);
-	bpf_iter_task_vma__destroy(skel);
+	bpf_iter_task_vmas__destroy(skel);
 }
 
 void test_bpf_sockmap_map_iter_fd(void)
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_vmas.c
similarity index 100%
rename from tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c
rename to tools/testing/selftests/bpf/progs/bpf_iter_task_vmas.c
-- 
2.34.1