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

Dave Marchevsky
2023-08-10T18:35:32Z

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.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Cc: Nathan Slingerland <slinger@meta.com>
---
include/uapi/linux/bpf.h | 5 ++
kernel/bpf/helpers.c | 3 +
kernel/bpf/task_iter.c | 56 +++++++++++++++++++
tools/include/uapi/linux/bpf.h | 5 ++
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
7 files changed, 90 insertions(+), 13 deletions(-)
rename tools/testing/selftests/bpf/progs/{bpf_iter_task_vma.c => bpf_iter_task_vmas.c} (100%)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index d21deb46f49f..c4a65968f9f5 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7291,4 +7291,9 @@ struct bpf_iter_num {
__u64 __opaque[1];
} __attribute__((aligned(8)));

+struct bpf_iter_task_vma {
+ __u64 __opaque[9]; /* See bpf_iter_num comment above */
+ char __opaque_c[3];
+} __attribute__((aligned(8)));
+
#endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index eb91cae0612a..7a06dea749f1 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2482,6 +2482,9 @@ 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)
+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 c4ab9d6cdbe9..76be9998a65a 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -8,6 +8,7 @@
#include <linux/fdtable.h>
#include <linux/filter.h>
#include <linux/btf_ids.h>
+#include <linux/mm_types.h>
#include "mmap_unlock_work.h"

static const char * const iter_task_type_names[] = {
@@ -823,6 +824,61 @@ const struct bpf_func_proto bpf_find_vma_proto = {
.arg5_type = ARG_ANYTHING,
};

+struct bpf_iter_task_vma_kern {
+ struct mm_struct *mm;
+ struct mmap_unlock_irq_work *work;
+ struct vma_iterator vmi;
+} __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 *i = (void *)it;
+ bool irq_work_busy = false;
+
+ 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));
+
+ BTF_TYPE_EMIT(struct bpf_iter_task_vma);
+
+ /* NULL i->mm signals failed bpf_iter_task_vma initialization.
+ * i->work == NULL is valid.
+ */
+ i->mm = NULL;
+ if (!task)
+ return -ENOENT;
+
+ i->mm = task->mm;
+ if (!i->mm)
+ return -ENOENT;
+
+ irq_work_busy = bpf_mmap_unlock_get_irq_work(&i->work);
+ if (irq_work_busy || !mmap_read_trylock(i->mm)) {
+ i->mm = NULL;
+ return -EBUSY;
+ }
+
+ vma_iter_init(&i->vmi, i->mm, addr);
+ return 0;
+}
+
+__bpf_kfunc struct vm_area_struct *bpf_iter_task_vma_next(struct bpf_iter_task_vma *it)
+{
+ struct bpf_iter_task_vma_kern *i = (void *)it;
+
+ if (!i->mm) /* bpf_iter_task_vma_new failed */
+ return NULL;
+ return vma_next(&i->vmi);
+}
+
+__bpf_kfunc void bpf_iter_task_vma_destroy(struct bpf_iter_task_vma *it)
+{
+ struct bpf_iter_task_vma_kern *i = (void *)it;
+
+ if (i->mm)
+ bpf_mmap_unlock_mm(i->work, i->mm);
+}
+
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/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index d21deb46f49f..c4a65968f9f5 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7291,4 +7291,9 @@ struct bpf_iter_num {
__u64 __opaque[1];
} __attribute__((aligned(8)));

+struct bpf_iter_task_vma {
+ __u64 __opaque[9]; /* See bpf_iter_num comment above */
+ char __opaque_c[3];
+} __attribute__((aligned(8)));
+
#endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index bbab9ad9dc5a..d885ffee4d88 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -302,6 +302,14 @@ 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